Any electrical circuits can be presented in the form of drawings (schematic and wiring diagrams), the design of which must comply with ESKD standards. These standards apply to both wiring or power circuits and electronic devices. Accordingly, in order to "read" such documents, it is necessary to understand the symbols in the electrical circuits.
Regulations
Considering a large number of electrical elements, for their alphanumeric (hereinafter BO) and conventionally graphic designations (UGO), a number of regulatory documents have been developed to exclude discrepancy. Below is a table showing the main standards.
Table 1. Standards for the graphic designation of individual elements in installation and circuit diagrams.
| GOST number | Short description |
| 2.710 81 | This document contains the requirements of GOST for BO of various types of electrical elements, including electrical appliances. |
| 2.747 68 | Requirements for the size of displaying elements in graphical form. |
| 21.614 88 | Accepted standards for electrical plans and wiring. |
| 2.755 87 | Display on diagrams of switching devices and contact connections |
| 2.756 76 | Standards for sensing parts of electromechanical equipment. |
| 2.709 89 | This standard regulates the standards according to which the contact connections and wires are indicated on the diagrams. |
| 21.404 85 | Schematic symbols for equipment used in automation systems |
It should be borne in mind that the element base changes over time, accordingly, changes are made to the regulatory documents, although this process is more inert. Let's give a simple example, RCDs and difavtomats have been widely used in Russia for more than a decade, but there is still no single standard for these devices in accordance with GOST 2.755-87, in contrast to circuit breakers... It is quite possible that this issue will be settled in the near future. To keep abreast of such innovations, professionals track changes in regulatory documents, amateurs do not need to do this, it is enough to know the decoding of the main designations.
Types of electrical circuits
In accordance with the norms of ESKD, diagrams mean graphic documents on which, using the accepted designations, the main elements or nodes of the structure are displayed, as well as the links that unite them. According to the accepted classification, ten types of circuits are distinguished, of which three are most often used in electrical engineering:
If the diagram shows only the power part of the installation, then it is called single-line, if all the elements are shown, then it is complete.
If the drawing shows the wiring of the apartment, then the locations of the lighting fixtures, sockets and other equipment are indicated on the plan. Sometimes you can hear how such a document is called a power supply scheme, this is incorrect, since the latter reflects the way consumers are connected to a substation or other power source.
Having dealt with the electrical circuits, we can proceed to the designations of the elements indicated on them.
Graphic symbols
For each type graphic document their designations are provided, regulated by the relevant regulatory documents. Let's give as an example the main graphic symbols for different types of electrical circuits.
Examples of UGO in functional diagrams
Below is a figure depicting the main components of automation systems.
Examples of symbols for electrical appliances and automation equipment in accordance with GOST 21.404-85 Description of designations:
- A - Basic (1) and allowed (2) images of devices that are installed outside the electrical panel or junction box.
- B - The same as point A, except that the elements are located on the console or electrical panel.
- С - Display of executive mechanisms (MI).
- D - Influence of IM on the regulatory body (hereinafter RO) when the power is turned off:
- Opening of RO
- Closing RO
- The position of the RO remains unchanged.
- E - IM, on which a manual drive is additionally installed. This symbol can be used for any position of the RO specified in clause D.
- F- Received communication lines display:
- General.
- There is no connection when crossing.
- The presence of a connection at the intersection.
UGO in single-line and complete wiring diagrams
There are several groups of symbols for these schemes, we will give the most common ones. To receive complete information it is necessary to refer to the regulatory documents, the numbers of state standards will be given for each group.
Power supplies.
For their designation, the symbols shown in the figure below are adopted.
UGO power supplies on schematic diagrams (GOST 2.742-68 and GOST 2.750.68) Description of designations:
- A - source with constant voltage, its polarity is indicated by the symbols "+" and "-".
- V is the electricity icon representing alternating voltage.
- C - the symbol for alternating and direct voltage, used in cases where the device can be powered from any of these sources.
- D - Display battery or galvanic power supply.
- E- Symbol for a multi-cell battery.
Communication lines
The basic elements of electrical connectors are shown below.
Designation of communication lines on schematic diagrams (GOST 2.721-74 and GOST 2.751.73) Description of designations:
- A - General mapping adopted for different types electrical connections.
- B - Current-carrying or grounding bus.
- C - Designation of shielding, can be electrostatic (marked with the symbol "E") or electromagnetic ("M").
- D - Grounding symbol.
- E - Electrical connection with the device body.
- F - On complex diagrams, from several component parts, a break in communication is thus indicated, in such cases "X" is information about where the line will be extended (as a rule, the element number is indicated).
- G - Intersection with no connection.
- H - Connection at the intersection.
- I - Branches.
Designations of electromechanical devices and contact connections
Examples of designation of magnetic starters, relays, as well as contacts of communication devices can be found below.
UGO, adopted for electromechanical devices and contactors (GOST 2.756-76, 2.755-74, 2.755-87) Description of designations:
- A - symbol of the coil of an electromechanical device (relay, magnetic switch etc.).
- B - UGO of the receiving part of the electrical thermal protection.
- С - display of the coil of the device with mechanical interlock.
- D - contacts of switching devices:
- Closing.
- Openers.
- Switching.
- E - Symbol for designation of manual switches (buttons).
- F - Group switch (switch).
UGO electric machines
Here are some examples of displaying electrical machines (hereinafter EM) in accordance with the current standard.
Designation of electric motors and generators on schematic diagrams (GOST 2.722-68) Description of designations:
- A - three-phase EM:
- Asynchronous (short-circuited rotor).
- Same as point 1, only in two-speed version.
- Asynchronous EMs with phase rotor design.
- Synchronous motors and generators.
- B - Collector, DC powered:
- EM with permanent magnet excitation.
- EM with an excitation coil.
UGO transformers and chokes
Examples of graphical symbols for these devices can be found in the figure below.
Correct designation of transformers, inductors and chokes (GOST 2.723-78) Description of designations:
- A - This graphic symbol can indicate inductors or transformer windings.
- B - Choke, which has a ferrimagnetic core (magnetic circuit).
- C - Display of a two-coil transformer.
- D - Device with three coils.
- E - Autotransformer symbol.
- F - Graphical display TT (current transformer).
Designation of measuring devices and radio components
A brief overview of the UGO data of electronic components is shown below. For those who want to become more familiar with this information, we recommend that you look through GOSTs 2.729 68 and 2.730 73.
Examples of conventional graphic symbols for electronic components and measuring instruments Description of designations:
- Electricity meter.
- Image of an ammeter.
- Mains voltage measuring device.
- Thermal sensor.
- Constant value resistor.
- Variable resistor.
- Condenser (general designation).
- Electrolytic capacity.
- Diode designation.
- Light-emitting diode.
- Image of a diode optocoupler.
- UGO transistor (in this case npn).
- Fuse designation.
UGO lighting fixtures
Consider how electric lamps are displayed on a schematic diagram.
Description of designations:
- A - General image of incandescent lamps (LN).
- B - LN as a signaling device.
- C - Type designation of discharge lamps.
- D - High pressure gas-discharge light source (the figure shows an example of a design with two electrodes)
Designation of elements in the wiring diagram
Completing the topic of graphic symbols, we give examples of the display of sockets and switches.
As depicted, sockets of other types are easy to find in the regulatory documents that are available on the network.
In the manufacture of electronic devices, novice radio amateurs may have difficulties in deciphering the designations on the diagram of various elements. For this, a small collection of the most common symbols for radio components was compiled. It should be noted that only the foreign version of the designation is given here and differences are possible on domestic schemes. But since most of the schemes and parts are of imported origin, this is quite justified. 
The resistor in the diagram is denoted by the Latin letter "R", the number is a conventional serial number according to the diagram. In the rectangle of the resistor, the nominal power of the resistor can be indicated - the power that it can dissipate for a long time without destruction. When current passes through the resistor, a certain power is dissipated, which leads to heating of the latter. Most foreign and modern domestic resistors are marked with colored stripes. Below is a table of color codes.
The most common designation system for semiconductor radio components is European. The main designation for this system consists of five characters. Two letters and three numbers - for a wide range of applications. Three letters and two numbers - for special equipment. The following letter denotes different parameters for devices of the same type.
The first letter is the material code:
A - germanium;
B - silicon;
C - gallium arsenide;
R is cadmium sulfide.
The second letter is the purpose:
A - low-power diode;
B - varicap;
C - low-power low-frequency transistor;
D - powerful low-frequency transistor;
E - tunnel diode;
F - low-power high-frequency transistor;
G - several devices in one case;
H - magnetic diode;
L - powerful high-frequency transistor;
M - Hall sensor;
Р - photodiode, phototransistor;
Q - LED;
R - low-power regulating or switching device;
S - low-power switching transistor;
T - powerful regulating or switching device;
U - powerful switching transistor;
X - multiplier diode;
Y - powerful rectifier diode;
Z - zener diode.
In this article, we will show a table of graphic designations of radioelements in the diagram.
A person who does not know the graphic designation of the elements of a radio circuit will never be able to "read" it. This material is intended to give a beginner radio amateur where to start. In various technical publications, such material is very rare. That is why he is valuable. In different publications there are "deviations" from the state standard (GOST) in the graphic designation of elements. This difference is important only for state acceptance bodies, and for a radio amateur it has no practical value, if only the type, purpose and main characteristics of the elements are clear. In addition, the designation may vary from country to country. Therefore, this article provides different options for the graphic designation of elements on the circuit (board). It may well be that you will not see all the designation options here.
Any element on the diagram has a graphic image and its alphanumeric designation. The shape and size of the graphic designation are determined by GOST, but as I wrote earlier, they have no practical value for the radio amateur. After all, if in the diagram, the image of the resistor is smaller in size than according to GOSTs, the radio amateur will not confuse it with another element. Any element is indicated on the diagram with one or two letters (the first is mandatory - uppercase), and a serial number on a specific diagram. For example, R25 means that this is a resistor (R), and in the diagram shown it is the 25th in a row. Serial numbers are usually assigned from top to bottom and left to right. It happens, when there are no more than two dozen elements, they are simply not numbered. It happens that when the circuits are revised, some elements with a "large" serial number may be in the wrong place in the circuit, according to GOST this is a violation. Obviously, the factory acceptance was bribed with a bribe in the form of a banal chocolate bar, or a bottle of an unusual shape of cheap cognac. If the circuit is large, then it can be difficult to find an out-of-order element. With a modular (block) construction of equipment, the elements of each block have their own serial numbers. Below you can familiarize yourself with the table containing the designations and descriptions of the main radio elements; for convenience, at the end of the article there is a link to download the table in WORD format.
Table of graphic designations of radioelements in the diagram
| Graphic designation (options) | Item name | Item Brief Description |
| Battery | Single source of electric current, including: watch batteries; finger salt batteries; dry rechargeable batteries; cell phone batteries | |
 | Battery of batteries | A set of single cells designed to power the equipment with increased total voltage (different from the voltage of a single cell), including: batteries of dry galvanic batteries; storage batteries of dry, acid and alkaline cells |
| Knot | Connection of conductors. The absence of a dot (circle) indicates that the conductors in the diagram intersect, but do not connect to each other - they are different conductors. Has no alphanumeric designation | |
 | Contact | Output of the radio circuit, designed for "hard" (usually screw) connection of conductors to it. Most often used in large power management and control systems of complex multi-block electrical circuits |
 | Nest | Connecting easily detachable contact of the "connector" type (in amateur radio slang - "mother"). It is mainly used for short-term, easily disconnected connection of external devices, jumpers and other circuit elements, for example, as a control socket |
| Power socket | A panel consisting of several (at least 2) "socket" contacts. Designed for multi-pin connection of radio equipment. A typical example is a household electrical outlet "220V" | |
| Plug | Contact easily detachable pin contact (in the slang of radio amateurs - "dad"), intended for short-term connection to the section of the electrical radio circuit | |
 | Fork | Multi-plug connector with at least two contacts intended for multi-pin connection of radio equipment. A typical example is the power plug of a household appliance "220V" |
| Switch | A two-contact device designed to close (open) an electrical circuit. A typical example is a light switch "220V" in a room | |
 | Switch | Three-contact device designed for switching electrical circuits. One contact has two possible positions |
 | Toggle switch | Two "paired" switches - switched simultaneously by one common handle. Separate groups contacts can be displayed in different parts of the diagram, then they can be designated as group S1.1 and group S1.2. In addition, with a large distance on the diagram, they can be connected by one dotted line. |
 | Gallet switch | The switch, in which one contact is of the "slide" type, can be switched to several different positions. There are paired switchgear switches, in which there are several groups of contacts |
 | Button | A two-contact device designed for short-term closing (opening) of an electrical circuit by pressing on it. A typical example is an apartment doorbell button |
| Common wire (GND) | Contact of the radio circuit, which has a conditional "zero" potential relative to the rest of the sections and connections of the circuit. Usually, this is the output of the circuit, the potential of which is either the most negative relative to the rest of the circuit sections (minus the circuit power supply), or the most positive (plus the circuit power supply). Has no alphanumeric designation | |
| Earthing | Circuit pin to be connected to Earth. Eliminates the possible occurrence of harmful static electricity, and also prevents electric shock in the event of a possible hit of dangerous voltage on the surface of radio devices and blocks that are touched by a person standing on wet ground. Has no alphanumeric designation | |
 | Incandescent lamp | An electrical device used for lighting. Under the action of an electric current, the glow of the tungsten filament (its combustion) occurs. The filament does not burn out because there is no chemical oxidizer inside the lamp bulb - oxygen |
 | Signal lamp | A lamp designed to control (signal) the state of various circuits of obsolete equipment. Currently, LEDs are used instead of signal lamps, which consume a weaker current and are more reliable. |
 | Neon lamp | Gas discharge lamp filled with inert gas. The glow color depends on the type of filler gas: neon - red-orange, helium - blue, argon - lilac, krypton - blue-white. Other methods are used to give a certain color to a lamp filled with neon - the use of fluorescent coatings (green and red glow) |
 | Daylight lamp (LDS) | A gas discharge lamp, including a miniature energy-saving lamp bulb, using a fluorescent coating — an afterglow chemistry. It is used for lighting. With the same power consumption, it has a brighter light than an incandescent lamp |
 | Electromagnetic relay | An electrical device designed to switch electrical circuits by supplying voltage to the electrical coil (solenoid) of the relay. The relay can have several groups of contacts, then these groups are numbered (for example, P1.1, P1.2) |
 | An electrical device designed to measure the strength of an electric current. It includes a stationary permanent magnet and a movable magnetic frame (coil), on which the arrow is attached. The greater the current flowing through the frame winding, the greater the angle the arrow deflects. Ammeters are divided according to the nominal current of the full deflection of the arrow, according to the accuracy class and according to the field of application. | |
 | An electrical device designed to measure the voltage of an electric current. In fact, it is no different from an ammeter, since it is made from an ammeter, by successively connecting to electrical circuit through an additional resistor. Voltmeters are divided according to the nominal voltage of the full deflection of the arrow, according to the accuracy class and according to the field of application. | |
 | Resistor | A radio device designed to reduce the current flowing through an electrical circuit. The diagram indicates the value of the resistance of the resistor. The power dissipation of the resistor is depicted with special stripes, or Roman symbols on graphic image case, depending on the power (0.125W - two oblique lines "//", 0.25 - one oblique line "/", 0.5 - one line along the resistor "-", 1W - one transverse line "I", 2W - two transverse lines "II", 5W - tick "V", 7W - tick and two transverse lines "VII", 10W - crosshair "X", etc.). For Americans, the designation of the resistor is zigzag, as shown in the figure |
| Variable resistor | A resistor, the resistance of which at its center terminal is regulated using a "knob-regulator". The nominal resistance indicated in the diagram is the total resistance of the resistor between its extreme terminals, which is not adjustable. Variable resistors can be paired (2 on one regulator) | |
| Trimmer resistor | A resistor, the resistance of which at its central terminal is adjusted using a "slot-regulator" - a hole for a screwdriver. As with a variable resistor, the nominal resistance indicated in the diagram is the total resistance of the resistor between its extreme terminals, which is not adjustable | |
| Thermistor | A semiconductor resistor whose resistance changes with ambient temperature. With an increase in temperature, the resistance of the thermistor decreases, and with a decrease in temperature, on the contrary, it increases. It is used to measure temperature as a thermal sensor, in thermal stabilization circuits of various stages of equipment, etc. | |
| Photoresistor | Resistor, the resistance of which changes depending on the illumination. With an increase in illumination, the resistance of the thermistor decreases, and with a decrease in illumination, on the contrary, it increases. It is used to measure illumination, register light fluctuations, etc. A typical example is the "light barrier" of a turnstile. Recently, instead of photoresistors, photodiodes and phototransistors are more often used. | |
 | Varistor | A semiconductor resistor that sharply decreases its resistance when the voltage applied to it reaches a certain threshold. The varistor is designed to protect electrical circuits and radio devices from accidental "surges" of voltage |
 | Capacitor | An element of a radio circuit with an electric capacity, capable of accumulating an electric charge on its plates. The application, depending on the size of the capacitance, is diverse, the most common radioelement after the resistor |
 | The capacitor, in the manufacture of which an electrolyte is used, due to this, with a relatively small size, has a much larger capacity than an ordinary "non-polar" capacitor. When using it, it is necessary to observe the polarity, otherwise the electrolytic capacitor loses its storage properties. It is used in power filters, as pass-through and storage capacitors for low-frequency and pulse equipment. An ordinary electrolytic capacitor self-discharges in no more than a minute, has the property of "losing" capacity due to the drying out of the electrolyte, to eliminate the effects of self-discharge and loss of capacity, more expensive capacitors are used - tantalum | |
| A capacitor whose capacity is regulated by means of a “slot-regulator” - holes for a screwdriver. Used in high-frequency circuits of radio equipment | ||
| A capacitor, the capacity of which is regulated by means of a handle (steering wheel) brought out to the outside of the radio receiving device. Used in high-frequency circuits of radio equipment as an element of a selective circuit that changes the tuning frequency of a radio transmitter or radio receiver | ||
| A high-frequency device with resonant properties similar to an oscillatory circuit, but at a certain fixed frequency. It can be used at "harmonics" - frequencies that are multiples of the resonant frequency indicated on the device body. Quartz glass is often used as a resonating element, therefore the resonator is called "quartz resonator", or simply "quartz". Used in generators of harmonic (sinusoidal) signals, clock generators, narrowband frequency filters and etc. | ||
 | Copper wire winding (coil). It can be frameless, on a frame, or it can be performed using a magnetic circuit (a core made of magnetic material). It has the property of accumulating energy due to the magnetic field. It is used as an element of high-frequency circuits, frequency filters and even an antenna of a receiving device | |
 | An adjustable inductance coil that has a movable core made of a magnetic (ferromagnetic) material. As a rule, it is wound on a cylindrical frame. Using a non-magnetic screwdriver, the depth of immersion of the core in the center of the coil is adjusted, thereby changing its inductance | |
 | An inductor containing a large number of turns, which is made using a magnetic circuit (core). Like a high frequency inductor, an inductor has energy storage properties. Used as elements of low-pass audio filters, power filter circuits and pulse accumulation | |
| An inductive element consisting of two or more windings. An alternating (changing) electric current applied to the primary winding creates a magnetic field in the transformer core, which in turn induces magnetic induction in the secondary winding. As a result, an electric current appears at the output of the secondary winding. Dots on the graphic designation at the edges of the transformer windings indicate the beginning of these windings, Roman numerals - the numbers of the windings (primary, secondary) | ||
 | A semiconductor device capable of passing current in one direction and not in the other. The direction of the current can be determined from the schematic image - converging lines, like an arrow, indicate the direction of the current. The conclusions of the anode and cathode are not indicated by letters on the diagram | |
 | A special semiconductor diode designed to stabilize the voltage of reverse polarity applied to its terminals (for a stabilizer - direct polarity) | |
| A special semiconductor diode that has an internal capacitance and changes its value depending on the amplitude of the voltage of reverse polarity applied to its terminals. It is used to form a frequency-modulated radio signal, in electronic control schemes for the frequency characteristics of radio receivers | ||
 | A special semiconductor diode, the crystal of which glows under the action of an applied direct current. It is used as a signal element for the presence of electric current in a certain circuit. There are different colors of the glow | |
| A special semiconductor diode, when illuminated, a weak electric current appears at the terminals. It is used to measure illumination, register light fluctuations, etc., like a photoresistor | |
 | A semiconductor device designed to switch an electrical circuit. When a small positive voltage is applied to the gate with respect to the cathode, the thyristor opens and conducts current in one direction (like a diode). The thyristor closes only after the disappearance of the current flowing from the anode to the cathode, or a change in the polarity of this current. The conclusions of the anode, cathode and control electrode are not indicated by letters on the diagram | |
| A composite thyristor capable of switching currents of both positive polarity (from anode to cathode) and negative (from cathode to anode). Like a thyristor, the triac closes only after the current flowing from the anode to the cathode disappears, or the polarity of this current changes. | ||
 | A type of thyristor that opens (starts to pass current) only when a certain voltage is reached between its anode and cathode, and is locked (stops passing current) only when the current decreases to zero, or the polarity of the current changes. Used in pulse control circuits | |
| A bipolar transistor that is controlled by a positive potential at the base relative to the emitter (the arrow at the emitter shows the conditional direction of the current). In this case, with an increase in the input voltage, the base-emitter from zero to 0.5 volts, the transistor is in the closed state. After further increasing the voltage from 0.5 to 0.8 volts, the transistor works as an amplifier. In the final section of the "linear characteristic" (about 0.8 volts), the transistor saturates (opens completely). A further increase in the voltage at the base of the transistor is dangerous, the transistor may fail (there is a sharp increase in the base current). According to the textbooks, a bipolar transistor is driven by a base-emitter current. The direction of the switched current in the n-p-n transistor is from the collector to the emitter. The conclusions of the base, emitter and collector are not indicated by letters in the diagram | ||
| A bipolar transistor that is driven by a negative potential at the base relative to the emitter (the arrow at the emitter shows the conditional direction of the current). According to the textbooks, a bipolar transistor is driven by a base-emitter current. The direction of the switched current in the pnp transistor is from the emitter to the collector. The conclusions of the base, emitter and collector are not indicated by letters in the diagram | ||
| Transistor (usually - n-p-n), the resistance of the junction "collector-emitter" which decreases when it is illuminated. The higher the illumination, the lower the transition resistance. It is used to measure illumination, register light oscillations (light pulses), etc., like a photoresistor | ||
 | A transistor, the resistance of the "drain-source" junction of which decreases when voltage is applied to its gate relative to the source. Has a high input impedance, which increases the sensitivity of the transistor to low input currents. It has electrodes: Gate, Source, Drain and Substrate (this is not always the case). By the principle of operation, it can be compared to a water tap. The greater the voltage at the gate (the valve handle is turned at a greater angle), the greater the current (more water) flows between the source and drain. Compared to a bipolar transistor, it has a wider range of regulating voltage - from zero to tens of volts. The terminals of the gate, source, drain and substrate are not indicated by letters on the diagram | |
 | A field-effect transistor controlled by a positive potential at the gate, relative to the source. Has an insulated shutter. It has a large input impedance and a very low output impedance, which allows small input currents to control large output currents. Most often, technologically, the substrate is connected to the source | |
 | A field-effect transistor, controlled by a negative potential at the gate, relative to the source (for storing the p-channel - positive). Has an insulated shutter. It has a large input impedance and a very low output impedance, which allows small input currents to control large output currents. Most often, technologically, the substrate is connected to the source | |
 | A field-effect transistor that has the same properties as the "built-in n-channel" with the difference that it has an even higher input impedance. Most often, the substrate is technologically connected to the source. Insulated gate technology uses MOSFET transistors controlled by an input voltage of 3 to 12 volts (depending on the type), having an open drain-source junction resistance of 0.1 to 0.001 Ohm (depending on the type) | |
 | A field-effect transistor that has the same properties as the "built-in p-channel" with the difference that it has an even higher input impedance. Most often, technologically, the substrate is connected to the source |
The ability to read electrical circuits is an important component, without which it is impossible to become a specialist in the field of electrical work. Every novice electrician must know how sockets, switches, switching devices and even an electricity meter are indicated on the wiring project in accordance with GOST. Further, we will provide the readers of the site with symbols in electrical circuits, both graphical and alphabetic.
Graphic
As for the graphic designation of all the elements used in the diagram, we will provide this overview in the form of tables, in which the products will be grouped by purpose.
In the first table, you can see how the electrical boxes, boards, cabinets and consoles are marked on the wiring diagrams:
The next thing you need to know is the conventional designation of power outlets and switches (including walk-throughs) on single-line diagrams of apartments and private houses:
With regard to lighting elements, lamps and lamps in accordance with GOST indicate as follows:
In more complex circuits where electric motors are used, elements such as:
It is also useful to know how transformers and chokes are graphically indicated on basic wiring diagrams:
Electrical measuring instruments in accordance with GOST have the following graphic designations in the drawings:
And here, by the way, is a table useful for novice electricians, which shows how the ground loop looks on the wiring plan, as well as the power line itself:
In addition, on the diagrams you can see a wavy or straight line, "+" and "-", which indicate the type of current, voltage and pulse shape:
In more complex automation schemes, you can find incomprehensible graphic symbols, such as contact connections. Remember how these devices are indicated on the wiring diagrams:
In addition, you should be aware of how radioelements look on projects (diodes, resistors, transistors, etc.):
That's all the conventionally graphic symbols in the electrical circuits of power circuits and lighting. As you have already seen for yourself, there are quite a few components and you can remember how each is designated only with experience. Therefore, we recommend that you keep all these tables for yourself, so that when reading the draft of the layout of the wiring of a house or apartment, you can immediately determine what kind of circuit element is in a certain place.
Interesting video
Popular science edition
Yatsenkov Valery Stanislavovich
Secrets of foreign radio circuits
Tutorial-reference for the master and the amateur
Editor A.I. Osipenko
Proofreader V.I. Kiseleva
Computer layout A.S. Varakin
B.C. Yatsenkov
SECRETS
FOREIGN
RADIO CIRCUIT
Reference tutorial
for the master and the amateur
Moscow
Major Publisher Osipenko A.I.
2004
Secrets of foreign radio circuits. Tutorial reference for
master and amateur. - M .: Major, 2004 .-- 112 p.
From the author
1. Basic types of schemes 1.1. Functional diagrams 1.2. Basic electrical diagrams 1.3. Visual images 2. Conventional graphic designations of elements of schematic diagrams 2.1. Conductors 2.2. Switches, connectors 2.3. Electromagnetic relays 2.4. Sources of electrical energy 2.5. Resistors 2.6. Capacitors 2.7. Coils and transformers 2.8. Diodes 2.9. Transistors 2.10. Dinistors, thyristors, triacs 2.11. Vacuum electronic tubes 2.12. Discharge lamps 2.13. Incandescent lamps and signal lamps 2.14. Microphones, sound emitters 2.15. Fuses and circuit breakers 3. Independent application of circuit diagrams step by step 3.1. Construction and analysis of a simple circuit 3.2. Analysis of a complex circuit 3.3. Assembly and debugging of electronic devices 3.4. Repair of electronic devices
The author refutes the widespread misconception that the reading of radio circuits and their use in the repair of household equipment is available only to trained specialists. A large number of illustrations and examples, a lively and accessible language of presentation make the book useful for readers with an initial level of knowledge of radio engineering. Particular attention is paid to the designations and terms used in foreign literature and documentation for imported household appliances.
FROM THE AUTHOR
First of all, dear reader, we thank you for your interest in this book.
The brochure you are holding is just the first step towards incredibly exciting knowledge. The author and publisher will consider their task accomplished if this book not only serves as a guide for beginners, but also gives them confidence in their abilities.
We will try to clearly show that for self-assembly of a simple electronic circuit or simple repair of a household appliance, you do not need to have big volume of special knowledge. Of course, to develop your own circuit, you will need knowledge of circuitry, that is, the ability to build a circuit in accordance with the laws of physics and in accordance with the parameters and purpose of electronic devices. But even in this case, one cannot do without the graphic language of schemes, in order to first correctly understand the material of the textbooks, and then correctly express his own thought.
While preparing the publication, we did not set ourselves the goal of retelling the content of GOSTs and technical standards in a condensed form. First of all, we appeal to those readers who are confused by an attempt to apply in practice or independently depict an electronic circuit. Therefore, the book covers only most commonly used symbols and designations, without which no scheme can do. Further reading and drawing skills will come to the reader gradually, as he gains practical experience. In this sense, learning the language of electronic circuits is like learning a foreign language: first we memorize the alphabet, then the simplest words and rules by which a sentence is built. Further knowledge comes only with intensive practice.
One of the problems faced by novice radio amateurs trying to repeat the scheme of a foreign author or repair a household device is that there is a discrepancy between the system of conventional graphic symbols (UGO), adopted earlier in the USSR, and the UGO system, operating in foreign countries. Due to the wide distribution of design programs supplied with UGO libraries (almost all of them are developed abroad), foreign circuit designations have also invaded domestic practice, despite the GOST system. And if an experienced specialist is able to understand the meaning of an unfamiliar symbol, based on the general context of the scheme, then for a beginner amateur this can cause serious difficulties.
In addition, the language of electronic circuits periodically undergoes changes and additions, the outline of some symbols changes. In this book, we will rely mainly on the international notation system, since it is it that is used in circuits for imported household equipment, in standard symbol libraries for popular computer programs and on pages of foreign websites. The designations that are officially outdated, but in practice are found in many schemes will also be mentioned.
1. MAIN TYPES OF CIRCUITS
In radio engineering, three main types of circuits are most often used: functional diagrams, schematic electrical diagrams and visual images. When studying the circuitry of any electronic device, as a rule, all three types of circuits are used, and it is in the order listed. In some cases, to improve clarity and convenience, the schemes can be partially combined.
Functional diagram gives a visual representation of the overall structure of the device. Each functionally complete unit is represented on the diagram as a separate block (rectangle, circle, etc.), indicating the function it performs. The blocks are connected to each other by solid or dashed lines, with or without arrows, in accordance with how they affect each other in the process.
Basic electrical diagram shows which components are included in the circuit and how they are connected to each other. The schematic diagram is often indicated by waveforms of signals and the magnitudes of voltage and current at test points. This type of schema is the most informative, and we will pay the most attention to it.
Visual images exist in several versions and are usually designed to facilitate installation and repair. These include the layout of the elements on the printed circuit board; layouts of connecting conductors; connection diagrams of individual nodes with each other; layouts of nodes in the body of the product, etc.
1.1. FUNCTIONAL DIAGRAMS
Rice. 1-1. Functional diagram examplecomplex of finished devices
Functional diagrams can be used for several different purposes. Sometimes they are used to show how various functionally complete devices interact with each other. An example is the connection diagram of a television antenna, a VCR, a television and an infrared remote control that controls them (Fig. 1-1). A similar diagram can be seen in any manual for the VCR. Looking at this diagram, we understand that the antenna must be connected to the input of the VCR in order to be able to record broadcasts, and the remote control is universal and can control both devices. Note that the antenna is shown using a symbol that is also used in circuit diagrams. Such a "mixing" of symbols is allowed in the case when a functionally complete unit is a part that has its own graphic designation. Looking ahead, we will say that the opposite situations also occur, when a part of a circuit diagram is depicted as a functional block.
If, when building a block diagram, priority is given to the image of the structure of a device or a complex of devices, such a diagram is called structural. If the block diagram is an image of several nodes, each of which performs a specific function, and the connections between the blocks are shown, then such a diagram is usually called functional. This division is somewhat arbitrary. For example, fig. 1-1 simultaneously shows both the structure of a home video complex and the functions performed by individual devices, and the functional connections between them.
When building functional diagrams, it is customary to follow certain rules. The main one is that the direction of the signal flow (or the order of execution of functions) is displayed in the drawing from left to right and from top to bottom. Exceptions are made only when the circuit has complex or bidirectional functional connections. Permanent connections, through which signals propagate, are made with solid lines, if necessary - with arrows. Irregular connections that act depending on a condition are sometimes shown with dashed lines. When developing a functional diagram, it is important to choose the right level of detail. For example, you should think about whether to represent the preliminary and final amplifiers in different blocks on the diagram, or one? It is desirable that the level of detail be the same for all components in the circuit.
As an example, consider the circuit of a radio transmitter with an amplitude-modulated output signal in Fig. 1-2a. It consists of a low frequency part and a high frequency part.
Rice. 1-2a. Functional diagram of the simplest AM transmitter
We are interested in the direction of transmission of the speech signal, we take its direction as a priority, and draw the low-frequency blocks at the top, from where the modulating signal, passing from left to right along the low-frequency blocks, enters down into the high-frequency blocks.
The main advantage of functional circuits is that universal circuits are obtained under the condition of optimal detailing. In different radio transmitters, completely different schematic diagrams of a master oscillator, modulator, etc. can be used, but their circuits with a low degree of detail will be absolutely the same.
It's another matter if deep detailing is used. For example, in one radio transmitter, the reference frequency source has a transistor multiplier, the other uses a frequency synthesizer, and the third uses a simple crystal oscillator. Then the detailed functional diagrams of these transmitters will be different. Thus, some nodes on the functional diagram, in turn, can also be represented in the form of a functional diagram.
Sometimes, in order to focus on a particular feature of the circuit or to increase its clarity, combined circuits are used (Fig. 1-26 and 1-2c), in which the image of functional blocks is combined with a more or less detailed fragment of a circuit diagram.
Rice. 1-2b. Combined circuit example
Rice. 1-2c. Combined circuit example
The block diagram shown in Fig. 1-2a is a kind of functional diagram. It does not show exactly how and by how many conductors the blocks are connected to each other. For this purpose serves interconnection diagram(fig. 1-3).
Rice. 1-3. An example of an interconnection diagram
Sometimes, especially when it comes to devices on logic chips or other devices operating according to a certain algorithm, it is necessary to schematically depict this algorithm. Of course, the algorithm of operation does not reflect much the peculiarities of constructing the electrical circuit of the device, but it can be very useful for repairing or adjusting it. When depicting an algorithm, they usually use standard symbols used in documenting programs. In fig. Figures 1-4 show the most commonly used symbols.
As a rule, they are sufficient to describe the algorithm for the operation of an electronic or electromechanical device.
As an example, consider a fragment of the algorithm of the washing machine automation unit (Fig. 1-5). After turning on the power, the presence of water in the tank is checked. If the tank is empty, the inlet valve opens. The valve is then held open until the high level sensor is triggered.
Algorithm start or end
An arithmetic operation performed by a program, or some action performed by a device
Comment, explanation or description
Input or output operation
Library module of the program
Jump on condition
Unconditional jump
Interstitial transition
Connecting lines
Rice. 1-4. Basic symbols for describing algorithms
Rice. 1-5. An example of the algorithm of the automation unit
1.2. PRINCIPAL
ELECTRICAL CIRCUITS
For a long time, at the time of Popov's first radio receiver, there was no clear distinction between visual and schematic diagrams. The simplest devices of that time were quite successfully depicted in the form of a slightly abstracted drawing. And now in textbooks you can find an image of the simplest electrical circuits in the form of drawings, in which the details are shown approximately as they actually look and how their conclusions are connected to each other (Fig. 1-6).
Rice. 1-6. Example of the difference between wiring diagram (A)
and a circuit diagram (B).
But for a clear understanding of what a circuit diagram is, you should remember: the arrangement of the symbols on the circuit diagram does not necessarily correspond to the actual arrangement of the components and connecting wires of the device. Moreover, a common mistake novice radio amateurs make when designing a printed circuit board on their own is to try to place components as close as possible to the order in which they are shown in the circuit diagram. Typically, the optimal placement of components on a board differs significantly from the placement of symbols on a circuit diagram.
So, on the schematic electrical diagram, we see only conventional graphic designations of the elements of the device circuit with an indication of their key parameters (capacitance, inductance, etc.). Each component of the circuit is numbered in a certain way. In the national standards of different countries regarding the numbering of elements, there are even greater discrepancies than in the case of graphic symbols. Since we set ourselves the task of teaching the reader to understand the circuits depicted according to "Western" standards, we will give a short list of the main letter designations of the components:
| Literal designation | Meaning | Meaning |
| ANT | Antenna | Antenna |
| IN | Battery | Battery |
| WITH | Capacitor | Capacitor |
| SV | Circuit Board | Circuit board |
| CR | Zener Diode | Zener diode |
| D | Diode | Diode |
| EP or Earphone | NS | Headphones |
| F | Fuse | Fuse |
| I | Lamp | Incandescent lamp |
| IC | Integrated circuit | Integrated circuit |
| J | Receptacle, Jack, Terminal Strip | Socket, cartridge, terminal block |
| TO | Relay | Relay |
| L | Inductor, choke | Coil, choke |
| LED | Light-emitting diode | Light-emitting diode |
| M | Meter | Meter (generalized) |
| N | Neon lamp | Neon lamp |
| R | Plug | Plug |
| PC | Photocell | Photocell |
| Q | Transistor | Transistor |
| R | Resistor | Resistor |
| RFC | Radio frequency choke | High frequency choke |
| RY | Relay | Relay |
| S | Switch | Switch, switch |
| SPK | Speaker | Speaker |
| T | Transformer | Transformer |
| U | Integrated circuit | Integrated circuit |
| V | Vacuum tube | Radio tube |
| VR | Voltage regulator | Regulator (stabilizer) eg. |
| X | Solar cell | Solar element |
| XTAL or Crystal | Quartz resonator Y | |
| Z | Circuit assembly | Circuit assembly assembly |
| ZD | Zener Diode (rare) | Zener diode (obsolete) |
Many circuit components (resistors, capacitors, etc.) may appear in the drawing more than once, therefore a digital index is added to the letter designation. For example, if there are three resistors in the circuit, then they will be designated as R1, R2 and R3.
Schematic diagrams, like block diagrams, are arranged in such a way that the input of the circuit is on the left and the output is on the right. An input signal also means a power source if the circuit is a converter or regulator, and an output means a power consumer, an indicator or an output stage with output terminals. For example, if we draw a flash lamp circuit, then we draw from left to right in order the mains plug, transformer, rectifier, pulse generator and flash lamp.
Elements are numbered from left to right and from top to bottom. In this case, the possible placement of elements on the printed circuit board has nothing to do with the numbering order - the circuit diagram has the highest priority in relation to other types of circuits. An exception is made when, for greater clarity, the circuit diagram is divided into blocks corresponding to the functional diagram. Then a prefix corresponding to the block number on the functional diagram is added to the element designation: 1-R1, 1-R2, 2L1, 2L2, etc.
In addition to the alphanumeric index, next to the graphic designation of the element, its type, brand or denomination are often written, which are of fundamental importance for the operation of the circuit. For example, for a resistor, this is the resistance value, for a coil - inductance, for a microcircuit - manufacturer's marking. Sometimes information on the ratings and marking of components is taken out in a separate table. This method is convenient in that it allows you to give extended information about each component - winding data of coils, special requirements for the type of capacitors, etc.
1.3. VISUAL IMAGES
The schematic diagrams and functional block diagrams complement each other well and are easy to understand with minimal experience. Nevertheless, very often these two diagrams are not enough for a full understanding of the design of the device, especially when it comes to its repair or assembly. In this case, several types of visual images are used.
We already know that schematic electrical diagrams do not show the physical essence of installation, and this task is solved by visual images. But, unlike block diagrams, which may be the same for different electrical circuits, pictorial images are inseparable from their corresponding circuit diagrams.
Let's look at some examples of illustrative images. In fig. 1-7 shows a type of wiring diagram - a wiring diagram of connecting conductors assembled in a shielded bundle, and the figure most closely matches the laying of conductors in a real device. Note that sometimes, to facilitate the transition from a circuit diagram to a wiring diagram, the color coding of the conductors and the symbol of the shielded wire are also indicated on the circuit diagram.
Rice. 1-7. Example of a wiring diagram for connecting conductors
The next widely used type of visual images are various layouts of elements. Sometimes they are combined with a wire layout. The circuit shown in Fig. 1-8 gives us enough information about the components that make up a microphone amplifier circuit for us to purchase, but says nothing about the physical dimensions of the components, board and case, or the placement of the components on the board. But In many cases, the placement of components on the board and / or in the case is critical to the reliable operation of the device.
Rice. 1-8. Scheme of the simplest microphone amplifier
The previous diagram is successfully complemented by the wiring diagram in Fig. 1-9. This is a two-dimensional diagram, it can show the length and width of the case or board, but not the height. If it is necessary to indicate the height, then a side view is given separately. The components are depicted as symbols, but their pictograms have nothing to do with UGO, but are closely related to the actual appearance of the part. Of course, supplementing such a simple schematic diagram with an installation diagram may seem superfluous, but this cannot be said about more complex devices consisting of tens and hundreds of parts.
Rice. 1-9. A visual representation of the installation for the previous circuit
The most important and most common type of wiring diagram is layout of elements on a printed circuit board. The purpose of such a circuit is to indicate the order of placing electronic components on the board during installation and to make it easier to find them during repair (recall that the arrangement of components on the board does not correspond to their location on the schematic diagram). One of the options for a visual representation of the printed circuit board is shown in Fig. 1-10. In this case, although conditionally, the shape and dimensions of all components are shown quite accurately, and their symbols are numbered, which coincides with the numbering on the circuit diagram. Dotted outlines show items that may be missing on the board.
Rice. 1-10. PCB Image Option
This option is convenient for repairs, especially when a specialist is working who, from his own experience, knows the characteristic appearance and dimensions of almost all radio components. If the circuit consists of many small and similar elements, and for repair it is required to find many control points(for example, to connect an oscilloscope), then the work becomes much more complicated even for a specialist. In this case, the coordinate layout of the elements comes to the rescue (Fig. 1-1 1).
Rice. 1-11. Coordinate layout of elements
The coordinate system used is somewhat similar to the coordinates on a chessboard. In this example, the board is divided into two, designated by the letters A and B, longitudinal parts (there may be more) and transverse parts provided with numbers. The image of the board is supplemented element placement table, an example of which is given below:
| Ref Desig | Grid Loc | Ref Desig | Grid Loc | Ref Desig | Grid Loc | Ref Desig | Grid Loc | Ref Desig | Grid Loc |
| C1 | B2 | C45 | A6 | Q10 | R34 | A3 | R78 | B7 | |
| C2 | B2 | C46 | A6 | Q11 | R35 | A4 | R79 | B7 | |
| C3 | B2 | C47 | A7 | Q12 | B5 | R36 | A4 | R80 | B7 |
| C4 | B2 | C48 | B7 | Q13 | R37 | A4 | R81 | B8 | |
| C5 | B3 | C49 | A7 | Q14 | A8 | R38 | B4 | R82 | B7 |
| C6 | B3 | C50 | A7 | Q15 | A8 | R39 | A4 | R83 | B7 |
| C7 | B3 | C51 | A7 | Q16 | B5 | R40 | A4 | R84 | B7 |
| C8 | B3 | C52 | A8 | Q17 | R41 | R85 | B7 | ||
| C9 | B3 | C53 | 018 | R42 | R86 | B7 | |||
| C10 | B3 | C54 | Q19 | B8 | R43 | B3 | R87 | Al | |
| C11 | B4 | C54 | A4 | Q20 | A8 | R44 | A4 | R88 | A6 |
| C12 | B4 | C56 | A4 | Rl | B2 | R45 | A4 | R89 | B6 |
| C13 | B3 | C57 | B6 | R2 | B2 | R46 | A4 | R90 | B6 |
| C14 | B4 | C58 | B6 | R3 | B2 | K47 | R91 | A6 | |
| C15 | A2 | CR1 | OT | R4 | OT | R48 | R92 | A6 | |
| C16 | A2 | CR2 | B3 | R5 | OT | R49 | AT 5 | R93 | A6 |
| C17 | A2 | CR3 | B4 | R6 | AT 4 | R50 | R94 | A6 | |
| C18 | A2 | CR4 | R7 | AT 4 | R51 | AT 5 | R93 | A6 | |
| C19 | A2 | CR5 | A2 | R8 | AT 4 | R52 | AT 5 | R94 | A6 |
| C20 | A2 | CR6 | A2 | R9 | AT 4 | R53 | A3 | R97 | A6 |
| C21 | A3 | CR7 | A2 | R10 | AT 4 | R54 | A3 | R98 | A6 |
| C22 | A3 | CR8 | A2 | R11 | AT 4 | R55 | A3 | R99 | A6 |
| C23 | A3 | CR9 | RI2 | R56 | A3 | R101 | A7 | ||
| C24 | B3 | CR10 | A2 | RI3 | R57 | OT | R111 | A7 | |
| C25 | A3 | CR11 | A4 | RI4 | A2 | R58 | OT | R112 | A6 |
| C26 | A3 | CR12 | A4 | RI5 | A2 | R39 | OT | R113 | A7 |
| C27 | A4 | CR13 | AT 8 | R16 | A2 | R60 | B5 | R104 | A7 |
| C28 | AT 6 | CR14 | A6 | R17 | A2 | R61 | AT 5 | R105 | A7 |
| C29 | AT 3 | CR15 | A6 | R18 | A2 | R62 | R106 | A7 | |
| C30 | CR16 | A7 | R19 | A3 | R63 | AT 6 | R107 | A7 | |
| C31 | AT 5 | L1 | AT 2 | R20 | A2 | R64 | AT 6 | R108 | A7 |
| C32 | AT 5 | L2 | AT 2 | R21 | A2 | R65 | AT 6 | R109 | A7 |
| SPZ | A3 | L3 | OT | R22 | A2 | R66 | AT 6 | R110 | A7 |
| C34 | A3 | L4 | OT | R23 | A4 | R67 | AT 6 | U1 | A1 |
| C35 | AT 6 | L5 | A3 | R24 | A3 | R6S | AT 6 | U2 | A5 |
| S36 | AT 7 | Q1 | OT | R2S | A3 | R69 | AT 6 | U3 | AT 6 |
| C37 | AT 7 | Q2 | AT 4 | R26 | A3 | R7U | AT 6 | U4 | AT 7 |
| C38 | AT 7 | Q3 | Q4 | R27 | AT 2 | R71 | AT 6 | U5 | A6 |
| C39 | AT 7 | Q4 | R28 | A2 | R72 | AT 7 | U6 | A7 | |
| C40 | AT 7 | Q5 | AT 2 | R29 | R73 | AT 7 | |||
| C41 | AT 7 | Q6 | A2 | R30 | R74 | AT 7 | |||
| C42 | AT 7 | O7 | A3 | R31 | OT | R75 | AT 7 | ||
| C43 | AT 7 | Q8 | A3 | R32 | A3 | R76 | AT 7 | ||
| C44 | AT 7 | Q9 | A3 | R33 | A3 | R77 | AT 7 |
When designing a printed circuit board using one of the design programs, the placement table can be generated automatically. The use of the table greatly facilitates the search for elements and control points, but increases the amount of design documentation.
In the manufacture of printed circuit boards in the factory, they are very often marked with designations similar to Fig. 1-10 or fig. 1-11. is also a kind of pictorial montage. It can be supplemented with the physical contours of the elements to facilitate the installation of the circuit (Fig. 1-12). 
Rice. 1-12. Drawing of the conductors of the printed circuit board.
It should be noted that the development of a printed circuit board design begins with the placement of elements on a board of a given size. When placing the elements, their shape and size, the possibility of mutual influence, the need for ventilation or shielding, etc. are taken into account.
2. SYMBOLS OF THE ELEMENTS OF THE CIRCUIT DIAGRAMS
As we already mentioned in Chapter 1, conventional graphic symbols (UGO) of radio electronic components used in modern circuitry have a rather distant relationship to the physical essence of a particular radio component. An example is the analogy between a schematic diagram of a device and a city map. On the map, we see an icon representing a restaurant, and we understand how to get to the restaurant. But this icon does not say anything about the restaurant's menu and prices for ready-made meals. In turn, the graphic symbol denoting a transistor on the diagram does not say anything about the size of the case of this transistor, whether it has flexible leads, and which company made it.
On the other hand, on the map next to the designation of the restaurant, the schedule of its work can be indicated. Similarly, near the UGO components on the diagram, important technical parameters of the part are usually indicated, which are of fundamental importance for the correct understanding of the diagram. For resistors, this is resistance, for capacitors - capacitance, for transistors and microcircuits - alphanumeric designation, etc.
Since its inception, UGO electronic components have undergone significant changes and additions. At first, these were fairly naturalistic drawings of details, which then, over time, were simplified and abstracted. Nevertheless, to make it easier to work with symbols, most of them still carry some hint of the design features of the real part. Talking about graphic symbols, we will try to show this relationship as much as possible.
Despite the seeming complexity of many electrical circuit diagrams, understanding them requires little more work than understanding a roadmap. There are two different approaches to acquiring the skill of reading circuit diagrams. Proponents of the first approach believe that UGO is a kind of alphabet, and one should first memorize it as fully as possible, and then start working with schemes. Proponents of the second method believe that you need to start reading diagrams almost immediately, studying unfamiliar symbols along the way. The second method is good for the radio amateur, but, alas, it does not teach a certain rigor of thinking necessary for the correct representation of the circuits. As you will see later, the same diagram can be depicted in very different ways, some of which are extremely difficult to read. Sooner or later, there will be a need to depict your own scheme, and this should be done so that it is understandable at first glance not only to the author. We leave the reader the right to independently decide which approach is closer to him, and move on to studying the most common graphic symbols.
2.1. CONDUCTORS
Most circuits contain a significant number of conductors. Therefore, the lines representing these conductors in the diagram often intersect, while there is no contact between the physical conductors. Sometimes, on the contrary, it is necessary to show the connection of several conductors to each other. In fig. 2-1 shows three options for crossing conductors.
Rice. 2-1. Options for the image of the intersection of conductors
Option (A) denotes a crossover conductor connection. In the case of (B) and (C), the conductors are not connected, but the designation (C) is considered obsolete and should be avoided in practice. Of course, the intersection of mutually insulated conductors in the schematic diagram does not mean their constructive intersection.
Several conductors can be combined into a bundle or cable. If the cable does not have a braid (screen), then, as a rule, these conductors are not particularly distinguished on the diagram. There are special symbols for shielded wires and cables (Figures 2-2 and 2-3). An example of a shielded conductor is a coaxial antenna cable.
Rice. 2-2. Single shielded conductor symbols with ungrounded (A) and grounded (B) shield
Rice. 2-3. Symbols for shielded cable with ungrounded (A) and grounded (B) shield
Sometimes the connection needs to be made with a twisted pair of conductors.
Rice. 2-4. Two options for designating a twisted pair of wires
In Figures 2-2 and 2-3, in addition to the conductors, we see two new graphic elements that will continue to appear. Dotted closed contour denotes a screen, which can be structurally made in the form of a braid around the conductor, in the form of a closed metal case, a separating metal plate or mesh.
The shield prevents the penetration of interference into circuits that are sensitive to external pickups. The next symbol is an icon representing a connection to a common wire, frame or ground. In circuitry, several symbols are used for this.
Rice. 2-5. Common wire and various grounding designations
The term "grounding" has a long history and goes back to the days of the first telegraph lines, when the Earth was used as one of the conductors to save wires. At the same time, all telegraph devices, regardless of their connection with each other, were connected to the Earth by means of grounding. In other words, the Earth was common wire. In modern circuitry, ground refers to a common or potential-free wire, even if it is not connected to the classic ground (Figure 2-5). The common wire can be isolated from the device body.
Very often, the body of the device is used as a common wire, or the common wire is electrically connected to the body. In this case, symbols (A) and (B) are used. Why are they different? There are circuits that combine analog components, such as operational amplifiers and digital ICs. To avoid mutual interference, especially from digital to analog circuits, use a separate common wire for analog and digital circuits. They are commonly referred to as "analog ground" and "digital ground". Similarly, common wires are shared for low-current (signal) and power circuits.
2.2. SWITCHES, CONNECTORS
A switch is a device, mechanical or electronic, that allows you to modify or break an existing connection. The switch allows, for example, to send a signal to any element of the circuit or to bypass this element (Fig. 2-6).
Rice. 2-6. Switches and switches
A special case of a switch is a switch. In fig. 2-6 (A) and (B) show single and double switches, and fig. 2-6 (C) and (D) are single and double switches, respectively. These switches are called two-position, since they have only two stable positions. As you can easily see, the switch and switch symbols depict the corresponding mechanical structures in sufficient detail and have hardly changed since their inception. Currently, this design is only used in power electrical circuit breakers. Low-current electronic circuits use tumblers and slide switches. For toggle switches, the designation remains the same (Figure 2-7), and for slide switches, a special designation is sometimes used (Figure 2-8).
The switch is usually shown in the diagram in off state, unless specifically stated the need to display it on.
Multi-position switches are often required to switch a large number of signal sources. They can also be single and double. The most convenient and compact design have rotary multi-position switches(Figure 2-9). This switch is often referred to as a "biscuit" switch because it emits a sound like the crunch of a dry biscuit being broken when it is switched. Dotted line between individual symbols (groups) of the switch means a rigid mechanical connection between them. If, due to the peculiarities of the scheme, the switching groups cannot be placed side by side, then an additional group index is used to designate them, for example, S1.1, S1.2, S1.3. In this example, three mechanically connected groups of one switch S1 are designated in this way. When depicting such a switch in the diagram, it is necessary to ensure that the switch slider is set to the same position for all groups.
Rice. 2-7. Symbols of different variants of toggle switches
Rice. 2-8. Slider switch symbol
Rice. 2-9. Multi Position Rotary Switches
The next group of mechanical switches are pushbutton switches and switches. These devices differ in that they are triggered not by shifting or rotating, but by pressing.
In fig. Figures 2-10 show the symbols for pushbutton switches. There are buttons with normally open contacts, normally closed, single and double, as well as switching single and double. There is a separate, although rarely used, designation for the telegraph key (manual generation of Morse code), shown in Fig. 2-11.
Rice. 2-10. Various push button options
Rice. 2-11. Special symbol for telegraph key
Use connectors to intermittently connect external lead wires or components to the circuit (Figure 2-12).
Rice. 2-12. Common connector designations
Connectors are divided into two main groups: jacks and plugs. The exception is some types of clamping connectors, for example, the charger contacts for the handset of the radiotelephone.
But even in this case, they are usually depicted in the form of a socket (charger) and a plug (a telephone handset inserted into it).
In fig. 2-12 (A) depict symbols for wall outlets and Western plugs. Symbols with filled rectangles represent plugs, to the left of them - symbols of the corresponding sockets.
Further in Fig. 2-12 depicts: (B) - an audio jack for connecting headphones, a microphone, low-power speakers, etc.; (C) - "tulip" type connector, usually used in video equipment for connecting cables of audio and video channels; (D) - RF coaxial cable connector. A filled circle in the center of a symbol indicates a plug, and an open circle indicates a jack.
Connectors can be combined into contact groups when it comes to a multi-pin connector. In this case, the symbols of the single contacts are graphically combined using a solid or dashed line.
2.3. ELECTROMAGNETIC RELAYS
Electromagnetic relays can also be referred to as a switch group. But, unlike buttons or toggle switches, contacts in a relay switch under the influence of the force of attraction of an electromagnet.
If the contacts are closed when the winding is de-energized, they are called normally closed, otherwise - normally open.
There are also changeover contacts.
The diagrams, as a rule, show the position of the contacts with a de-energized winding, if this is not specifically mentioned in the description of the circuit.
Rice. 2-13. Relay design and designation
The relay can have several contact groups acting synchronously (Fig. 2-14). In complex circuits, the relay contacts can be shown separately from the coil symbol. The relay in the complex or its winding is designated by the letter K, and a digital index is added to the alphanumeric designation to designate the contact groups of this relay. For example, K2.1 denotes the first contact group of the K2 relay.
Rice. 2-14. Relays with one and several contact groups
In modern foreign circuits, the relay winding is increasingly indicated as a rectangle with two leads, as has long been accepted in domestic practice.
In addition to conventional electromagnetic ones, polarized relays are sometimes used, a distinctive feature of which is that the armature switches from one position to another when the polarity of the voltage applied to the winding changes. In the de-energized state, the armature of the polarized relay remains in the position it was in before the power was turned off. Currently, polarized relays are practically not used in common circuits.
2.4. ELECTRIC POWER SOURCES
Sources of electrical energy are divided into primary: generators, solar cells, chemical sources; and secondary: converters and rectifiers. Both those and others can either be depicted on a schematic diagram, or not. It depends on the features and purpose of the circuit. For example, in the simplest diagrams, very often instead of a power source, only connectors for its connection are shown, indicating the nominal voltage, and sometimes the current consumed by the circuit. Indeed, for a simple amateur radio design, it doesn't really matter whether it is powered by a Krona battery or a laboratory rectifier. On the other hand, a household appliance usually includes a built-in mains power supply, and it will necessarily be shown in the form of a detailed diagram in order to facilitate the maintenance and repair of the product. But this will be a secondary source of power supply, since we would have to indicate the generator of the hydroelectric power station and intermediate transformer substations as the primary source, which would be quite pointless. Therefore, on the diagrams of devices powered from public mains, they are limited to the image of the mains plug.
On the contrary, if the generator is an integral part of the design, it is depicted in a schematic diagram. An example is the schemes on-board network a car or an autonomous generator driven by an internal combustion engine. There are several common generator symbols (Figure 2-15). Let us comment on these designations.
(A) is the most common alternator symbol.
(B) - used when it is necessary to indicate that the voltage is removed from the generator winding using spring contacts (brushes) pressed against circular rotor leads. These generators are commonly used in automobiles.
(C) is a generalized symbol of a structure in which the brushes are pressed against the segmented rotor (collector) leads, that is, to the contacts in the form of metal pads located around the circumference. This symbol is also used to denote electric motors of a similar design.
(D) - filled elements of the symbol indicate that brushes made of graphite are used. The letter A indicates an abbreviation for the word Alternator- alternator, in contrast to the possible designation D - Direct Current- direct current.
(E) - indicates that it is the generator shown, and not the electric motor, denoted by the letter M, if this is not obvious from the context of the diagram.
Rice. 2-15. Basic schematic symbols of the generator
The segmented collector mentioned above, used in both generators and electric motors, has its own symbol (Figure 2-16).
Rice. 2-16. Segmented manifold symbol with graphite brushes
Structurally, the generator consists of rotor coils rotating in the stator magnetic field, or stator coils located in an alternating magnetic field created by a rotating rotor magnet. In turn, the magnetic field can be created by both permanent magnets and electromagnets.
To power the electromagnets, called field windings, a part of the electricity generated by the generator itself is usually used (an additional current source is needed to start the operation of such a generator). By adjusting the current in the excitation winding, you can adjust the amount of voltage generated by the generator.
Consider three main circuits for switching on the excitation winding (Fig. 2-17).
Of course, the diagrams are simplified and only illustrate the basic principles of constructing a generator circuit with a bias winding.
Rice. 2-17. Options for the generator circuit with excitation winding
L1 and L2 - excitation windings, (A) - sequential circuit, in which the magnitude of the magnetic field is greater, the greater the consumed current, (B) - parallel circuit, in which the magnitude of the excitation current is set by the regulator R1, (C) - combined circuit.
Much more often than a generator, chemical current sources are used as a primary source to power electronic circuits.
Regardless of whether it is a battery or a consumable chemical element, they are indicated in the same diagram on the diagram (Fig. 2-18).
Rice. 2-18. Designation of chemical current sources
A single cell, an example of which in everyday life can be a conventional finger-type battery, is depicted as shown in Fig. 2-18 (A). The series connection of several such cells is shown in Fig. 2-18 (B).
And finally, if the current source is a structurally inseparable battery of several cells, it is depicted as shown in Fig. 2-18 (C). The number of conditional cells in this symbol does not necessarily match the actual number of cells. Sometimes, if it is necessary to especially emphasize the features of a chemical source, additional inscriptions are placed next to it, for example:
NaOH - alkaline battery;
H2SO4 - sulfuric acid battery;
Lilon - lithium-ion battery;
NiCd - nickel-cadmium battery;
NiMg - nickel metal hydride battery;
Rechargeable or Rech.- some rechargeable source (battery);
Non-Rechargeable or N-Rech.- non-rechargeable source.
Solar cells are often used to power low-power devices.
The voltage generated by one cell is low, therefore, batteries from series-connected solar cells are usually used. Batteries like these are often seen in calculators.
A commonly used designation for a solar cell and solar battery shown in Fig. 2-19.
Rice. 2-19. Solar cell and solar cell
2.5. RESISTORS
About resistors it is safe to download that it is the most commonly used component of electronic circuits. Resistors have a large number of design options, but the main conventions are presented in three versions: fixed resistor, fixed point-tapped (discrete-variable) and variable. Examples of appearance and the corresponding conventions are shown in Fig. 2-20.
Resistors can be made of a material that is sensitive to temperature or light changes. Such resistors are called thermistors and photoresistors, respectively, and their symbols are shown in Fig. 2-21.
Several other designations can also be found. In recent years, magnetoresistive materials that are sensitive to changes in the magnetic field have become widespread. As a rule, they are not used as separate resistors, but are used as part of magnetic field sensors and, especially often, as a sensitive element of the read heads of computer drives.
Currently, the ratings of almost all small-sized permanent resistors are indicated by color-coded rings.
Ratings can be different in a very wide range - from units of Ohms to hundreds of megohms (millions of Ohms), but their exact values, however, are strictly standardized and can only be selected from among the permitted values.
This is done in order to avoid a situation where different manufacturers start producing resistors with arbitrary rows of values, which would greatly complicate the development and repair of electronic devices. The color coding of the resistors and a range of acceptable values are given in Appendix 2.
Rice. 2-20. The main types of resistors and their graphic symbols
Rice. 2-21. Thermistors and photoresistor
2.6. CONDENSERS
If we called resistors the most commonly used component of circuits, then capacitors are in second place in terms of frequency of use. They have a greater variety of designs and symbols than resistors (Figure 2-22).
There is a basic division into capacitors of fixed and variable capacitance. Fixed capacitors, in turn, are divided into groups depending on the type of dielectric, plates and physical form. The simplest capacitor is made of aluminum foil in the form of long strips, which are separated by a paper dielectric. The resulting layered combination is rolled to reduce bulk. Such capacitors are called paper capacitors. They have many disadvantages - small capacity, large dimensions, low reliability, and they are not currently used. Much more often, a polymer film is used in the form of a dielectric, with metal plates deposited on both sides. Such capacitors are called film capacitors.
Rice. 2-22. Various types of capacitors and their designations In accordance with the laws of electrostatics, the capacitance of a capacitor is the greater, the smaller the distance between the plates (dielectric thickness). The highest specific capacity is possessed by electrolytic capacitors. One of the plates in them is a metal foil covered with a thin layer of a strong non-conductive oxide. This oxide plays the role of a dielectric. A porous material impregnated with a special conductive liquid - electrolyte - is used as the second plate. Due to the fact that the dielectric layer is very thin, the capacity of the electrolytic capacitor is large.
An electrolytic capacitor is sensitive to the polarity of the connection in the circuit: if it is turned on incorrectly, a leakage current appears, leading to the dissolution of the oxide, the decomposition of the electrolyte and the release of gases that can break the capacitor case. On the conventional graphic designation of an electrolytic capacitor, both symbols, "+" and "-" are sometimes indicated, but more often they indicate only a positive terminal.
Variable capacitors can also be of different designs. Pa fig. 2-22 shows options for variable capacitors with air dielectric. Such capacitors were widely used in tube and transistor circuits of the past to tune the oscillatory circuits of receivers and transmitters. There are not only single, but double, triple and even quad variable capacitors. The disadvantage of variable air-dielectric capacitors is their cumbersome and complex design. After the appearance of special semiconductor devices - varicaps, capable of changing the internal capacitance depending on the applied voltage, mechanical capacitors almost disappeared from use. Now they are mainly used to tune the output stages of transmitters.
Small-sized trimmer capacitors are often made in the form of a ceramic base and rotor, on which metal segments are sprayed.
To indicate the capacitance of capacitors, color coding in the form of dots and body colors, as well as alphanumeric markings, are often used. The capacitor marking system is described in Appendix 2.
2.7. COILS AND TRANSFORMERS
Various inductors and transformers, also referred to as winding products, can be designed in completely different ways. The main design features of the winding products are reflected in conventional graphic symbols. Inductors, including inductively coupled ones, are denoted by the letter L, and transformers by the letter T.
The way the inductor is wound is called winding or stacking wires. Various coil designs are shown in fig. 2-23.
Rice. 2-23. Various coil designs
If the coil is made of several turns of thick wire and retains its shape only due to its rigidity, such a coil is called frameless. Sometimes, to increase the mechanical strength of the coil and increase the stability of the resonant frequency of the circuit, a coil, even made of a small number of turns of a thick wire, is wound on a non-magnetic dielectric frame. The frame is usually made of plastic.
The inductance of the coil increases significantly if a metal core is placed inside the winding. The core can be threaded and can move within the frame (Figure 2-24). In this case, the coil is called tunable. In passing, we note that the introduction of a core made of a non-magnetic metal, such as copper or aluminum, into the coil, on the contrary, reduces the inductance of the coil. Typically, screw cores are used only for fine tuning of oscillating circuits designed for a fixed frequency. For quick tuning of the circuits, the variable capacitors mentioned in the previous section, or varicaps, are used.
Rice. 2-24. Customizable inductors
Rice. 2-25. Ferrite core coils
When the coil operates in the radio frequency range, cores made of transformer iron or other metal are usually not used, since eddy currents arising in the core heat the core, which leads to energy losses and significantly reduces the Q-factor of the circuit. In this case, the cores are made of a special material - ferrite. Ferrite is a solid mass, similar in properties to ceramics, consisting of a very fine powder of iron or its alloy, where each metal particle is isolated from the others. As a result, no eddy currents are generated in the core. The ferrite core is usually denoted by broken lines.
The next extremely common winding product is the transformer. At its core, a transformer is two or more inductors located in a common magnetic field. Therefore, the windings and core of the transformer are depicted by analogy with the symbols of the inductors (Fig. 2-26). An alternating magnetic field created by an alternating current flowing through one of the coils (primary winding) leads to the excitation of an alternating voltage in the remaining coils (secondary windings). The magnitude of this voltage depends on the ratio of the number of turns in the primary and secondary windings. The transformer can be step-up, step-down or isolating, but this property is usually not displayed in any way on a graphic symbol, signing the input or output voltage values next to the winding terminals. In accordance with the basic principles of building circuits, the primary (input) winding of the transformer is depicted on the left, and the secondary (output) - on the right.
Sometimes it is necessary to show which pin is the beginning of the winding. In this case, a dot is placed near it. The windings are numbered in Roman numerals on the diagram, but the numbering of the windings is not always applied. When a transformer has several windings, to distinguish between the terminals, they are numbered on the transformer case, near the corresponding terminals, or made of conductors of different colors. In fig. 2-26 (C) shows for example appearance a mains power supply transformer and a fragment of a circuit that uses a transformer with several windings.
In fig. 2-26 (D) and 2-26 (E) show, respectively, buck and boost autotransformers.
Rice. 2-26. Conditional graphic symbols of transformers
2.8. DIODES
A semiconductor diode is the simplest and one of the most commonly used semiconductor components, also called solid state components. Structurally, a diode is a semiconductor junction with two leads - a cathode and an anode. A detailed consideration of the principle of operation of a semiconductor junction is beyond the scope of this book, so we will limit ourselves only to describing the relationship between the diode device and its symbol.
Depending on the material used for the manufacture of the diode, the diode can be germanium, silicon, selenium, and by design, point or planar, but in the diagrams it is indicated by the same symbol (Fig. 2-27).
Rice. 2-27. Some diode designs
Sometimes the diode symbol is enclosed in a circle to show that the crystal is placed in a case (there are also unpackaged diodes), but now this designation is rarely used. In accordance with the domestic standard, diodes are depicted with an open triangle and a through line passing through it, connecting the leads.
The graphical designation of a diode has a long history. In the first diodes, a semiconductor junction was formed at the point of contact of a metal needle contact with a flat substrate made of a special material, for example, lead sulphide.
In this design, the triangle represents a needle contact.
Subsequently, planar diodes were developed in which a semiconductor junction occurs on the contact plane of n - and p - type semiconductors, but the diode designation remains the same.
We have already mastered enough conventions to easily read the simple diagram shown in Fig. 2-28, and understand how it works.
As it should be, the circuit is built in the direction from left to right.
It begins with a picture of the mains plug in the "western" standard, followed by a mains transformer and a diode rectifier built on a bridge circuit, commonly called a diode bridge. The rectified voltage is supplied to a certain payload, conventionally designated by the resistance Rn.
Quite often there is a variant of the image of the same diode bridge, shown in Fig. 2-28 on the right.
Which option is preferable to use is determined only by the convenience and clarity of the outline of a specific scheme.
Rice. 2-28. Two variants of the outline of the diode bridge circuit
The considered circuit is very simple, so understanding the principle of its operation does not cause difficulties (Fig. 2-29).
Consider, for example, the typeface shown on the left.
When a half-wave of an alternating voltage from the transformer secondary is applied so that the top terminal is negative and the bottom is positive, electrons move in series through diode D2, load, and diode D3.
When the polarity of the half-wave is reversed, electrons move through diode D4, load, and diode DI. As you can see, regardless of the polarity of the acting half-wave of the alternating current, electrons flow through the load in the same direction.
Such a rectifier is called full-wave, because both half-cycles of the alternating voltage are used.
Of course, the current through the load will be pulsating, since the alternating voltage changes sinusoidally, passing through zero.
Therefore, in practice, most rectifiers use high-capacity smoothing electrolytic capacitors and electronic stabilizers.
Rice. 2-29. The movement of electrons through diodes in a bridge circuit
Most voltage regulators are based on another semiconductor device, which is very similar in design to a diode. In domestic practice, it is called Zener diode, and in foreign circuitry, a different name is adopted - Zener diode(Zener Diode), named after the scientist who discovered the tunnel breakdown effect pn junction.
The most important property of the zener diode is that when the reverse voltage at its terminals reaches a certain value, the zener diode opens and current begins to flow through it.
An attempt to further increase the voltage leads only to an increase in the current through the zener diode, but the voltage at its terminals remains constant. This tension is called voltage stabilization. So that the current through the zener diode does not exceed the permissible value, they include in series with it damping resistor.
There are also tunnel diodes, which, on the contrary, have the property of maintaining a constant current flowing through them.
In common household appliances, tunnel diodes are rare, mainly in the nodes for stabilizing the current flowing through a semiconductor laser, for example, in CD-ROM drives.
But such assemblies, as a rule, cannot be repaired and maintained.
The so-called varicaps or varactors are much more common in everyday life.
When a reverse voltage is applied to a semiconductor junction and it is closed, then the junction has some capacity, like a capacitor. Wonderful p-n property transition is that when the voltage applied to the transition changes, the capacitance also changes.
Making the transition according to a certain technology, they achieve that it has a sufficiently large initial capacity, which can vary within wide limits. This is why mechanical variable capacitors are not used in modern portable electronics.
Optoelectronic semiconductor devices are extremely common. They can be quite complex in design, but in fact they are based on two properties of some semiconductor junctions. LEDs capable of emitting light when current flows through the junction, and photodiodes- change its resistance when changing the illumination of the transition.
LEDs are classified according to the wavelength (color) of the light emitted.
The light color of the LED is practically independent of the amount of current flowing through the junction, but is determined by the chemical composition of the additives in the materials that form the junction. LEDs can emit both visible light and invisible infrared light. Recently, ultraviolet LEDs have been developed.
Photodiodes are also subdivided into those that are sensitive to visible light and operate in the range invisible to the human eye.
A well-known example of a LED-photodiode pair is a TV remote control system. The remote control has an infrared LED, and the TV has a photodiode of the same range.
Regardless of the radiation range, LEDs and photodiodes are identified by two generic symbols (Figure 2-30). These symbols are close to the current Russian standard, are very clear and do not cause any difficulties.
Rice. 2-30. Legend of the main optoelectronic devices
If you combine an LED and a photodiode in one housing, you get optocoupler. It is a semiconductor device ideal for galvanic isolation of circuits. With its help, it is possible to transmit control signals without electrically connecting the circuits. This is sometimes very important, for example, in switching power supplies, where it is necessary to galvanically separate the sensitive control circuit and high-voltage switching circuits.
2.9. TRANSISTORS
Without a doubt, transistors are the most commonly used active components of electronic circuits. The transistor symbol does not reflect its internal structure too literally, but there is some relationship. We will not analyze in detail the principle of operation of the transistor, many textbooks are devoted to this. Transistors are bipolar and field. Consider the structure of a bipolar transistor (Figure 2-31). A transistor, like a diode, consists of semiconductor materials with special additives. NS- and p-type, but has three layers. The thin separation layer is called base, the other two are emitter and collector. A substitute property of the transistor is that if the emitter and collector leads are sequentially connected to an electrical circuit containing a power source and a load, then small changes in the current in the base-emitter circuit lead to significant, hundreds of times larger, changes in the current in the load circuit. Modern transistors are capable of controlling load voltages and currents thousands of times higher than base voltages or currents.
Depending on the order in which the layers of semiconductor materials are located, bipolar transistors of the type rpr and npn... In the graphical representation of the transistor, this difference is reflected in the direction of the arrow of the emitter terminal (Figure 2-32). The circle indicates that the transistor has a housing. If it is necessary to indicate that an unpackaged transistor is used, as well as when depicting the internal circuit of transistor assemblies, hybrid assemblies or microcircuits, transistors are depicted without a circle.
Rice. 2-32. Graphic designation of bipolar transistors
When drawing circuits containing transistors, they also try to follow the principle of "input from the left - output from the right".
In fig. 2-33 in accordance with this principle, three standard circuits for switching on bipolar transistors are simplified: (A) - with a common base, (B) - with a common emitter, (C) - with a common collector. In the image of the transistor, one of the variants of the outline of the symbol used in foreign practice is used.
Rice. 2-33. Options for turning on the transistor in the circuit
A significant disadvantage of a bipolar transistor is its low input impedance. A low-power signal source with high internal resistance may not always provide the base current required for normal operation of the bipolar transistor. Field-effect transistors are devoid of this drawback. Their design is such that the current flowing through the load does not depend on the input current through the control electrode, but on the potential across it. Due to this, the input current is so small that it does not exceed the leakage in the insulating materials of the installation, and therefore it can be neglected.
There are two main options for the design of a field-effect transistor: with a control pn-junction (JFET) and channel field-effect transistor with the structure "metal-oxide-semiconductor" (MOSFET, in Russian abbreviation MOS-transistor). These transistors have different designations. First, let's get acquainted with the designation of a JFET transistor. Depending on the material from which the conductive channel is made, field-effect transistors are distinguished NS- and p- type.
Pa fig. 2-34 show the structure of a field-effect transistor and the legend of field-effect transistors with both types of conduction.
This figure shows that gate, made of p-type material, is located above a very thin channel made of w-type semiconductor, and on both sides of the channel there are "-type zones to which the leads are connected source and drain. The materials for the channel and the gate, as well as the operating voltages of the transistor, are selected in such a way that, under normal conditions, the resulting rn- the junction is closed and the gate is isolated from the channel. The current in the load, sequentially flowing in the transistor through the source terminal, the channel and the drain terminal, depends on the potential at the gate.
Rice. 2-34. The structure and designation of the channel field-effect transistor
A conventional field-effect transistor, in which the gate is isolated from the channel by a closed / w-junction, is simple in design and very common, but in the last 10-12 years its place has been gradually taken by field-effect transistors, in which the gate is made of metal and is isolated from the channel by the thinnest oxide layer ... Such transistors are usually designated abroad by the abbreviation MOSFET (Metal-Oxide-Silicon Field Effect Transistor), and in our country - by the abbreviation MOS (Metal-Oxide-Semiconductor). The metal oxide layer is a very good dielectric.
Therefore, in MOS transistors, the gate current is practically absent, while in a conventional field-effect transistor it, although very small, is noticeable in some applications.
It should be especially noted that MOS transistors are extremely sensitive to the effects of static electricity on the gate, since the oxide layer is very thin and exceeding the permissible voltage leads to breakdown of the insulator and damage to the transistor. When installing or repairing devices containing MOSFETs, special measures must be taken. One of the methods popular with radio amateurs is this: before installation, the transistor leads are wrapped with several turns of a thin bare copper vein, which is removed with tweezers after the end of the soldering.
The soldering iron must be grounded. Some transistors are protected by built-in Schottky diodes, through which static electricity flows.
Rice. 2-35. Enriched MOSFET structure and designation
Depending on the type of semiconductor from which the conductive channel is made, MOS transistors are distinguished NS- and p-type.
In the designation on the diagram, they differ in the direction of the arrow on the substrate pin. In most cases, the substrate does not have its own terminal and is connected to the source and body of the transistor.
In addition, MOSFETs are enriched and impoverished type. In fig. 2-35 show the structure of an enriched n-type MOSFET. For a p-type transistor, the channel and substrate materials are swapped. A characteristic feature of such a transistor is that the conductive n-channel occurs only when the positive voltage at the gate reaches the required value. The inconsistency of the conductive channel on the graphic symbol is reflected by the dashed line.
The structure of the depleted MOSFET and its graphic symbol are shown in Fig. 2-36. The difference is that NS- the channel is always present even when no voltage is applied to the gate, so the line between the source and drain pins is solid. The substrate is also most often connected to the source and body and does not have its own terminal.
In practice, they also apply two-gate Lean type MOSFETs, the design and designation of which are shown in Fig. 2-37.
Such transistors are very useful when it becomes necessary to combine signals from two different sources, for example, in mixers or demodulators.
Rice. 2-36. The structure and designation of a depleted MOSFET transistor
Rice. 2-37. The structure and designation of a two-gate MOS transistor
2.10. DINISTORS, THYRISTORS, SYMISTORS
Now that we have discussed the designations of the most popular semiconductor devices, diodes and transistors, we will get acquainted with the designations of some other semiconductor devices that are also often found in practice. One of them - deac or bidirectional diode thyristor(Figure 2-38).
In structure, it is similar to two diodes connected in anti-series, except that the n-region is common and is formed rpr structure with two transitions. But, unlike a transistor, in this case, both transitions have exactly the same characteristics, due to which this device is electrically symmetrical.
A rising voltage of either polarity meets a relatively high resistance of a junction connected in reverse polarity until the reverse-biased junction transitions to an avalanche breakdown state. As a result, the resistance of the reverse transition drops sharply, the current flowing through the structure increases, and the voltage at the terminals decreases, forming a negative current-voltage characteristic.
Diacs are used to control any devices depending on the voltage, for example, to switch thyristors, turn on lamps, etc.
Rice. 2-38. Bidirectional diode thyristor (diac)
The next device abroad is referred to as a controlled silicon diode (SCR, Silicon Controlled Rectifier), and in domestic practice - triode thyristor, or trinistor(Figure 2-39). In terms of its internal structure, a triode thyristor is a structure of four alternating layers with different types of conductivity. This structure can be conventionally represented as two bipolar transistors with different conductivity.
Rice. 2-39. Triode thyristor (SCR) and its designation
Trinistor works as follows. When turned on correctly, the SCR is connected in series with the load so that the positive potential of the power source is applied to the anode, and negative to the cathode. In this case, the current does not flow through the SCR.
When a positive voltage is applied to the control junction relative to the cathode and it reaches a threshold value, the SCR abruptly switches to a conducting state with a low internal resistance. Further, even if the control voltage is removed, the SCR remains in a conducting state. The thyristor goes into the closed state only if the anode-cathode voltage becomes close to zero.
In fig. 2-39 shows a voltage controlled SCR with respect to the cathode.
If the SCR is voltage controlled with respect to the anode, the gate line depicts the gate away from the anode triangle.
Due to their ability to remain open after switching off the control voltage and the ability to switch large currents, SCRs are very widely used in power circuits such as controlling electric motors, lighting lamps, high-power voltage converters, etc.
The disadvantage of SCRs is that they depend on the correct polarity of the applied voltage, which is why they cannot work in AC circuits.
Symmetrical triode thyristors or triacs, having a name abroad triac(Figure 2-40).
The triac symbol is very similar to the diac symbol, but has a gate lead. Triacs operate on any polarity of the supply voltage applied to the main terminals and are used in a variety of designs where it is necessary to control an AC load.
Rice. 2-40. Triac (triac) and its designation
Bidirectional switches (symmetric keys) are used somewhat less often, which, like a trinistor, have a structure of four alternating layers with different conductivity, but two control electrodes. A symmetric switch goes into a conducting state in two cases: when the anode-cathode voltage reaches the level of avalanche breakdown, or when the anode-cathode voltage is less than the breakdown level, but a voltage is applied to one of the control electrodes.
Rice. 2-41. Bi-directional switch (symmetric key)
Oddly enough, but for the designation of a diac, trinistor, si-mistor and a bidirectional switch abroad there are no generally accepted letter designations, and on the diagrams next to the graphic designation a number is often written with which this component designates a specific manufacturer (which is very inconvenient, since it generates confusion when there are several identical parts).
2.11. ELECTRONIC VACUUM LAMPS
At first glance, with the current level of development of electronics, it is simply inappropriate to talk about vacuum electronic tubes (in everyday life - radio tubes).
But this is not the case. In some cases, vacuum tubes are still in use. For example, some hi-fi audio amplifiers are manufactured using vacuum tubes, as such amplifiers are believed to have a special, soft and clear sound that transistor circuits cannot achieve. But this question is very complex - just as the circuits of such amplifiers are complex. Alas, such a level is not available to a novice radio amateur.
Much more often radio amateurs are faced with the use of radio tubes in power amplifiers for radio transmitters. There are two ways to achieve high power output.
First, using high voltage at low currents, which is quite simple from the point of view of building a power source - you just need to use a step-up transformer and a simple rectifier containing diodes and smoothing capacitors.
And, secondly, operating with low voltages, but at high currents in the circuits of the output stage. This option requires a powerful stabilized power supply, which is quite complex, dissipates a lot of heat, is bulky and very expensive.
Of course, there are specialized high-frequency high-frequency transistors that operate at higher voltages, but they are very expensive and rarely found.
In addition, they still significantly limit the permissible output power, and cascade circuits for switching on several transistors are difficult to manufacture and debug.
Therefore, transistor output stages in radio transmitters with a power of more than 15 ... 20 watts are usually used only in industrial equipment or in products of experienced radio amateurs.
In fig. 2-42 show the elements from which the designations of various versions of electronic tubes are "assembled". Let's take a quick look at the purpose of these elements:
(1) - Filament for heating the cathode.
If a directly heated cathode is used, this also denotes the cathode.
(2) - Indirectly heated cathode.
It is heated with a thread indicated by the symbol (1).
(3) - Anode.
(4) - Grid.
(5) - Reflective indicator lamp anode.
This anode is covered with a special phosphor and glows under the influence of an electron flow. Currently, it is practically not used.
(6) - Forming electrodes.
Designed to form a flow of electrons of the desired shape.
(7) - Cold cathode.
It is used in special type lamps and can emit electrons without heating, under the influence of an electric field.
(8) - Photocathode coated with a layer of a special substance that significantly increases the emission of electrons under the action of light.
(9) - Filler gas in gas-filled vacuum devices.
(10) - Hull. Obviously, there is no designation for a vacuum tube that does not contain a housing symbol. 
Rice. 2-42. Designations of various elements of radio tubes
Most tube names come from the number of basic elements. So, for example, a diode has only an anode and a cathode (the heating thread is not considered a separate element, since in the first radio tubes the heating thread was covered with a layer of a special substance and at the same time was a cathode; such radio tubes are still found today). The use of vacuum diodes in amateur practice is very rarely justified, mainly in the manufacture of high-voltage rectifiers for powering the already mentioned powerful output stages of transmitters. And even then, in most cases, they can be replaced by high-voltage semiconductor diodes.
In fig. 2-43 show the main options for the design of radio tubes that can be found in the manufacture of an amateur design. In addition to the diode, this is a triode, tetrode and pentode. Twin tubes are common, such as a double triode or double tetrode (Figure 2-44). There are also radio tubes that combine two different design options in one housing, for example, a triode-pentode. It may happen that different parts of such a radio tube should be depicted in different parts of the schematic diagram. Then the body symbol is depicted not completely, but partially. Sometimes one half of the body symbol is depicted as a solid line, and the other half as a dotted line. All terminals at the radio tubes are numbered clockwise when looking at the lamp from the side of the terminals. The corresponding pin numbers are put on the diagram next to the graphic designation.
Rice. 2-43. Designations of the main types of radio tubes
Rice. 2-44. An example of the designation of composite radio tubes
And, finally, we will mention the most common electronic vacuum device that we all see in everyday life almost every day. This is a cathode ray tube (CRT), which, when it comes to a TV or computer monitor, is usually called a kinescope. There are two ways to deflect the flow of electrons: using a magnetic field created by special deflecting coils, or using an electrostatic field created by deflecting plates. The first method is used in televisions and displays, since it allows you to deflect the beam at a large angle with good accuracy, and the second - in oscilloscopes and other measuring equipment, since it works much better at high frequencies and does not have a pronounced resonant frequency. An example of the designation of a cathode-ray tube with electrostatic deflection is shown in Fig. 2-45. CRT with electromagnetic deflection is depicted in almost the same way, only instead of located inside deflection plate tubes beside outside depict deflecting coils. Very often, on the diagrams, the designations of the deflecting coils are not located next to the CRT designation, but where it is more convenient, for example, near the output stage of the horizontal or vertical scan. In this case, the purpose of the coil is indicated by the adjacent Horizontal Deflection. Horizontal Yoke or Vertical Deflection, Vertical Yoke.
Rice. 2-45. Cathode-ray tube designation
2.12. DISCHARGE LAMPS
Discharge lamps get their name in accordance with the principle of operation. It has long been known that between two electrodes placed in a rarefied gas environment, with sufficient voltage between them, a glow discharge occurs, and the gas begins to glow. Examples of gas discharge lamps include advertising sign lamps and indicator lamps for household appliances. Neon is most often used as a filling gas, therefore, very often abroad, gas-discharge lamps are denoted by the word "Neon", making the name of the gas a household name. In fact, gases can be different, up to mercury vapor, which gives invisible ultraviolet radiation ("quartz lamps").
Some of the most common designations for discharge lamps are shown in Fig. 2-46. Option (I) is very often used to indicate indicator lights to indicate mains power is on. Option (2) is more complicated, but similar to the previous one.
If the discharge lamp is sensitive to the polarity of the connection, use the designation (3). Sometimes the lamp bulb is covered from the inside with a phosphor, which glows under the influence of ultraviolet radiation generated by a glow discharge. By choosing the composition of the phosphor, it is possible to make very durable indicator lamps with different glow colors, which are still used in industrial equipment and are indicated by the symbol (4).
2-46. Common designations of gas discharge lamps
2.13. Incandescent and signaling lamps
The designation of the lamp (Fig. 2-47) depends not only on the design, but also on its purpose. So, for example, incandescent lamps in general, incandescent lighting lamps and incandescent lamps indicating the connection to the network can be indicated by the symbols (A) and (B). Signal lamps that indicate any modes or situations in the operation of the device are most often indicated by symbols (D) and (E). Moreover, it may not always be an incandescent lamp, so you should pay attention to the general context of the circuit. There is a special symbol (F) to indicate the flashing warning light. Such a symbol can be found, for example, in the electrical circuit of a car, where it is used to denote direction indicator lamps.
Rice. 2-47. Incandescent and signal lamp designations
2.14. MICROPHONES, SOUND TRANSMITTERS
Sound emitting devices can have a wide variety of designs based on various physical effects. In household appliances, the most common are dynamic loudspeakers and piezo emitters.
The generalized image of a loudspeaker in foreign circuitry coincides with the domestic UGO (Fig. 2-48, symbol 1). By default, this symbol is used to denote dynamic loudspeakers, that is, the most common loudspeakers in which the coil moves in a constant magnetic field and drives the cone. Sometimes it becomes necessary to emphasize the design features, and other designations are used. So, for example, symbol (2) denotes a speaker in which a magnetic field is generated by a permanent magnet, and symbol (3) denotes a speaker with a special electromagnet. Such electromagnets have been used in very powerful dynamic loudspeakers. Currently, DC bias loudspeakers are almost never used because relatively inexpensive, powerful and large permanent magnets are commercially available.
Rice. 2-48. Common speaker designations
Bells and buzzers (beepers) are also widely used sound emitters. A call, regardless of its purpose, is represented by the symbol (1) in Fig. 2-49. The buzzer is usually a high pitched electromechanical system and is very rarely used today. On the contrary, the so-called beepers ("tweeters") are used very often. They are installed in cell phones, pocket electronic games, electronic watches, etc. In the overwhelming majority of cases, the work of beepers is based on the piezomechanical effect. The crystal of a special piezo-substance contracts and expands under the influence of an alternating electric field. Sometimes beepers are used, which are similar in principle to dynamic loudspeakers, only very small-sized. Recently, it is not uncommon for beepers to incorporate a miniature electronic circuit that generates sound. It is enough just to apply a constant voltage to such a beeper for it to start sounding. Regardless of the design features, in most foreign circuits, beepers are denoted by the symbol (2), Fig. 2-49. If the polarity of inclusion is important, it is indicated near the terminals.
Rice. 2-49. Bells, Buzzers and Beepers
Headphones (in common parlance - headphones) have different designations in foreign circuitry, which do not always coincide with the domestic standard (Fig. 2-50).
Rice. 2-50. Headphone designations
If we consider schematic diagram tape recorder, music center or cassette player, then we will definitely meet the conventional designation of the magnetic head (Fig. 2-51). The UGOs shown in the figure are absolutely equivalent and represent a generalized designation.
If it is necessary to emphasize that we are talking about a reproducing head, then next to the symbol is an arrow pointing towards the head.
If the head is recording, then the arrow is directed away from the head, if the head is universal, then the arrow is bidirectional, or not displayed.
Rice. 2-51. Magnetic heads designations
Common microphone designations are shown in Fig. 2-52. Such symbols denote either microphones in general, or dynamic microphones, which are structurally arranged like dynamic loudspeakers. If the microphone is electret, when the sound vibrations of the air are perceived by the movable plate of the film capacitor, then the symbol of a non-polar condenser may be depicted inside the microphone symbol.
Electret microphones with a built-in preamplifier are very common. These microphones have three pins, one of which supplies power, and must be connected to the correct polarity. If it is necessary to emphasize that the microphone has a built-in amplifier stage, a transistor symbol is sometimes placed inside the microphone designation.
Rice. 2-52. Graphical Microphone Symbols
2.15. FUSES AND DISCONNECTORS
The obvious purpose of fuses and circuit breakers is to protect the rest of the circuit from damage in the event of an overload or failure of one of the components. In this case, the fuses burn out and require replacement during repair. When the threshold value of the current flowing through them is exceeded, the protective circuit breakers go into the open state, but most often they can be returned to the initial state by pressing a special button.
When repairing a device that "does not show signs of life", first of all, the mains fuses and fuses at the output of the power source are checked (rare, but found). If the device operates normally after replacing the fuse, it means that the mains voltage surge or other overload has caused the fuse to blown. Otherwise, there will be more serious repairs.
Modern switching power supplies, especially in computers, very often contain self-healing semiconductor rectifiers. These fuses usually take some time to restore conduction. This time is slightly longer than the simple cooling time. The situation when a computer that did not even turn on suddenly starts working normally after 15-20 minutes is explained by the restoration of the fuse.
Rice. 2-53. Fuses and Breakers
Rice. 2-54. Breaker with reset button
2.16. ANTENNAS
The location of the antenna symbol on the diagram depends on whether the antenna is receiving or transmitting. The receiving antenna is an input device, therefore it is located on the left, reading the receiver circuit begins from the antenna symbol. The transmitting antenna of the radio transmitter is placed on the right, and it completes the circuit. If a transmitter circuit is built - a device that combines the functions of a receiver and a transmitter, then, according to the rules, the circuit is depicted in reception mode and the antenna is most often placed on the left. If the device uses an external antenna connected via a connector, then very often only the connector is depicted, omitting the antenna symbol.
Generalized antenna symbols are very often used, Fig. 2-55 (A) and (B). These symbols are used not only in circuit diagrams, but also in functional diagrams. Some of the graphical symbols reflect the design features of the antenna. So, for example, in Fig. 2-55 symbol (C) stands for directional antenna, symbol (D) for dipole with balanced feeder, symbol (E) for dipole with asymmetric feeder.
The wide variety of antenna designations used in foreign practice does not allow considering them in detail, but most of the designations are intuitive and do not cause difficulties even for novice radio amateurs.
Rice. 2-55. Examples of external antennas
3. INDEPENDENT APPLICATION OF THE PRINCIPAL DIAGRAMS STEP BY STEP
So, we have briefly familiarized ourselves with the main graphic symbols elements of circuits. This is quite enough to start reading electrical circuit diagrams, at first the simplest, and then more complex. An untrained reader may object: "Perhaps I can understand a circuit consisting of several resistors and capacitors and one or two transistors. But I cannot quickly understand more complex scheme, for example, the circuit of a radio receiver. "This is an erroneous statement.
Yes, indeed, many electronic circuits look very complex and intimidating. But, in fact, they consist of several functional blocks, each of which is a less complex circuit. The ability to dismember a complex diagram into structural units is the first and main skill that the reader must acquire. Next, you should objectively cordon off the level of your own knowledge. Here are two examples. Let's say we are talking about repairing a VCR. Obviously, in this situation, a novice radio amateur is quite capable of finding a fault at the level of an open in the power circuits and even detecting missing contacts in the connectors of the ribbon cables of board-to-board connections. This requires at least a rough idea of the functional diagram of the VCR and the ability to read the circuit diagram. Repair of more complex units will be within the power of only an experienced craftsman and it is better to immediately refuse from attempts at random to eliminate the malfunction, since there is a high probability of aggravating the malfunction with unskilled actions.
Another thing is when you are going to repeat a relatively uncomplicated radio amateur design. Typically, such electronic circuits accompany detailed descriptions and installation diagrams. If you know the legend system, you can easily repeat the design. Surely later you will want to make changes to it, improve it or adapt it to the existing components. And the ability to dismember the circuit into its constituent functional blocks will play a huge role. For example, you can take a circuit that was originally designed for battery power and connect to it a mains supply "borrowed" from another circuit. Or use another low-frequency amplifier in a radio receiver - there can be many options.
3.1. CONSTRUCTION AND ANALYSIS OF A SIMPLE CIRCUIT
To understand the principle by which the finished circuit is mentally divided into functional units, we will do the reverse work: from the functional units we will build a circuit of a simple detector receiver. The RF portion of the circuit, which separates the baseband signal from the RF input signal, consists of an antenna, a coil, a variable capacitor, and a diode (Figure 3-1). This fragment of the diagram can be called simple, right? Besides the antenna, it consists of only three parts. Coil L1 and capacitor C1 form an oscillating circuit, which, from the set of electromagnetic oscillations received by the antenna, selects oscillations of only the desired frequency. Oscillations are detected (extraction of the low-frequency component) by means of diode D1.
Rice. 3-1. RF part of the receiver circuit
To start listening to radio broadcasts, it is enough to add high-impedance headphones connected to the output terminals to the circuit. But that doesn't suit us. We want to listen to radio broadcasts through a loudspeaker. The signal directly at the output of the detector has a very low power, therefore, in most cases, one amplifier stage is not enough. We decide to use a preamplifier, the circuit of which is shown in Fig. 3-2. This is another functional block of our radio receiver. Please note that a power source appeared in the circuit - battery B1. If we want to power the receiver from a network source, then we must depict either the terminals for connecting it, or the diagram of the source itself. For simplicity, we'll restrict ourselves to the battery.
The preamplifier circuit is very simple, it can be drawn in a couple of minutes and assembled in about ten.
After combining two functional units, a diagram of Fig. 3-3. At first glance, it has become more complex. But is it so? It is composed of two fragments that did not seem complicated in isolation. The dotted line shows where the imaginary dividing line is between functional nodes. If you understand the diagrams of the two previous nodes, then it will not be difficult to understand the general diagram. Please note that in the diagram in fig. 3-3, the numbering of some of the preamplifier elements has been changed. Now they are part of the general scheme and are numbered in general order exactly for this circuit.
Rice. 3-2. Receiver preamplifier
The signal at the output of the preamplifier is more powerful than at the output of the detector, but not sufficient to connect a loudspeaker. It is necessary to add another amplifier stage to the circuit, thanks to which the sound in the speaker will be loud enough. One of the possible variants of the functional unit is shown in Fig. 3-4.
Rice. 3-3. An intermediate variant of the receiver circuit
Rice. 3-4. Receiver output amplifier stage
Let's add an output amplifier stage to the rest of the circuit (Figure 3-5).
Connect the output of the preamplifier to the input of the final stage. (We cannot feed the signal directly from the detector to the output stage, because without pre-amplification, this signal is too weak.)
You probably noticed that the supply battery was depicted in both the preamplifier and final amplifier circuits, and in the final circuit it occurs only once.
In this circuit, there is no need for separate power supplies, so both amplifier stages in the final circuit are connected to the same supply.
Of course, in the form in which the diagram is shown in Fig. 3-5, it is unsuitable for practical use. The ratings of resistors and capacitors, alphanumeric designations of the diode and transistors, coil winding data are not indicated, there is no volume control.
Nevertheless, this scheme is very close to those used in practice.
Many radio amateurs begin their practice with the assembly of a radio receiver in a similar way.
Rice. 3-5. The final layout of the radio receiver
We can say that the main process in the development of circuits is combination.
First, at the level of a general idea, blocks of a functional diagram are combined.
The individual electronic components are then combined to form simple functional components of the circuit.
These, in turn, are combined into a more complex overall scheme.
Schemes can be combined with each other to build a functionally complete product.
Finally, products can be combined to build a hardware system such as a home theater system.
3.2. ANALYSIS OF A COMPLEX SCHEME
With some experience, analysis and combination are quite accessible even to a novice radio amateur or home craftsman when it comes to assembling or repairing simple household circuits.
You just need to remember that skill and understanding comes only with practice. Let's try to analyze a more complex circuit shown in Fig. 3-6. As an example, we use a circuit of an amateur radio AM transmitter for a range of 27 MHz.
This is a very real scheme, this or a similar scheme can often be found on radio amateur sites.
It is deliberately left in the form in which it is given in foreign sources, while preserving the original designations and terms. To facilitate the understanding of the diagram by novice radio amateurs, it is already divided by solid lines into functional blocks.
As expected, we will begin the consideration of the diagram from the upper left corner.
Located there, the first section contains the microphone preamplifier. Its simple circuit contains a single p-channel FET, whose input impedance matches the output impedance of an electret microphone.
The microphone itself is not shown in the diagram, only the connector for its connection is shown, and the type of microphone is indicated next to the text. Thus, the microphone can be from any manufacturer, with any alphanumeric designation, as long as it is electret and does not have a built-in amplifier stage. In addition to the transistor, the preamplifier circuit contains several resistors and capacitors.
The purpose of this circuit is to amplify the weak microphone output to a level sufficient for further processing.
The next section is the ULF, which consists of an integrated circuit and several external parts. The ULF amplifies the audio signal coming from the preamplifier output, as was the case with a simple radio receiver.
The amplified audio signal enters the third section, which is a matching circuit and contains a modulating transformer T1. This transformer is a matching element between the low-frequency and high-frequency parts of the transmitter circuit.
The low frequency current flowing in the primary winding causes changes in the collector current of the high frequency transistor flowing through the secondary winding.
Next, let's move on to examining the high-frequency part of the circuit, starting from the lower left corner of the drawing. The first high-frequency section is a quartz reference oscillator, which, thanks to the presence of a quartz resonator, generates radio frequency oscillations with good frequency stability.
This simple circuit contains just one transistor, several resistors and capacitors, and a high-frequency transformer consisting of coils L1 and L2, placed on a single frame with an adjustable core (depicted by an arrow). From the output of the L2 coil, the high-frequency signal is fed to the high-frequency power amplifier. The signal generated by the crystal oscillator is too weak to feed into the antenna.
And, finally, from the output of the RF amplifier, the signal goes to a matching circuit, the task of which is to filter out the side harmonic frequencies that arise when the RF signal is amplified, and to match the output impedance of the amplifier with the input impedance of the antenna. The antenna, like the microphone, is not shown in the diagram.
It can be of any design designed for this range and output power level.
Rice. 3-6. Amateur AM transmitter circuit
Take a look at this diagram again. Perhaps it no longer seems difficult to you? Of the six segments, only four contain active components (transistors and a microcircuit). This seemingly difficult diagram is actually a combination of six different simple schemes, each of which is easy to understand.
The correct order of displaying and reading diagrams has a very deep meaning. It turns out that it is very convenient to assemble and configure the device in exactly the order in which it is convenient to read the diagram. For example, if you have almost no experience in assembling electronic devices, the transmitter just discussed is best assembled, starting with a microphone amplifier, and then step by step, checking the operation of the circuit at each stage. This will save you from the tedious search for an installation error or a faulty part.
As for our transmitter, all fragments of its circuit, provided that the parts are in good order and correctly installed, should start working immediately. Only the high-frequency part requires tuning, and then after the final assembly.
First of all, we assemble the microphone amplifier. We check the correctness of installation. We connect the electret microphone to the connector and supply power. Using an oscilloscope, we make sure that there are undistorted amplified sound vibrations at the source terminal of the transistor when something is said into the microphone.
If this is not the case, it is necessary to replace the transistor, protecting it from breakdown by static electricity.
By the way, if you have a microphone with a built-in amplifier, then this stage is not needed. You can use a three-pin connector (to supply power to the microphone) and send the signal from the microphone through the blocking capacitor directly to the second stage.
If 12 volts is too high to power the microphone, add the simplest microphone power supply of a series-connected resistor and zener diode rated for the required voltage (usually 5 to 9 volts) to the circuit.
As you can see, even in the first steps there is room for creativity.
Next, we assemble in order the second and third sections of the transmitter. After we have made sure that amplified sound vibrations are present on the secondary winding of the transformer T1, we can consider the assembly of the low-frequency part complete.
The assembly of the high-frequency part of the circuit begins with the master oscillator. If there is no RF voltmeter, frequency meter or oscilloscope, the presence of generation can be verified using the receiver tuned to the desired frequency. You can also connect the simplest RF oscillation indicator to the L2 coil pin.
Then, the output stage is assembled, the matching circuit, the equivalent of the antenna is connected to the antenna connector and the final adjustment is made.
The procedure for adjusting the RF cascades. especially the weekend, is usually described in detail by the authors of the schemes. It can be different for different schemes and is beyond the scope of this book.
We have examined the relationship between the structure of the circuit and the order in which it is assembled. Of course, the schemes are not always so clearly structured. However, you should always try to break a complex circuit into functional units, even if they are not explicitly highlighted.
3.4. REPAIR OF ELECTRONIC DEVICES
As you may have noticed, we considered assembly of the transmitter in the order "from input to output". This makes it easier to debug the circuit.
But troubleshooting during repairs, it is customary to carry out in the reverse order, "from exit to entrance". This is due to the fact that the output stages of most circuits operate with relatively large currents or voltages and are much more likely to fail. For example, in the same transmitter, the reference crystal oscillator is practically not susceptible to malfunctions, while the output transistor can easily fail from overheating in the event of an open or short circuit in the antenna circuit. Therefore, if the transmitter's radiation is lost, first of all, the output stage is checked. Do the same with IF amplifiers in tape recorders, etc.
But before checking the components of the circuit, you need to make sure that the power supply is working properly and that the supply voltages are coming to the main board. Simple, so-called linear, power supplies can also be tested "from input to output", starting with the mains plug and fuse. Any experienced radio technician can tell you how many home appliances are brought into the workshop due to a faulty power cord or blown fuse. The situation with impulse sources is much more complicated. Even the simplest switching power supply circuits can contain very specific radio components and are usually covered in circuits feedbacks and mutually influencing adjustments. A single fault in such a source often leads to the failure of many components. Inappropriate actions can aggravate the situation. Therefore, the repair of the impulse source must be carried out by a qualified technician. Pi in no case should you neglect the safety requirements when working with electrical appliances. They are simple, well-known, and have been described many times in the literature.
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GOST 19880-74 |
Electrical engineering. Basic concepts. |
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GOST 1494-77 |
Letter designations. |
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GOST 2.004-79 |
Rules for the execution of design documents on printing and graphic output devices of computers. |
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Types and completeness of design documents. |
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Development stages. |
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Basic inscriptions. |
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GOST 2.105-79 |
General requirements for text documents. |
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GOST 2.106-68 |
Text documents. |
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GOST 2.109-73 |
Basic requirements for drawings. |
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GOST 2.201-80 |
Designations of products and design documents. |
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Formats. |
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GOST 2.302-68 |
The scale. |
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GOST 2.303-68 |
Lines. |
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GOST 2.304-81 |
Drawing fonts. |
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GOST 2.701-84 |
Schemes. Types and types. General requirements for implementation. |
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GOST 2.702-75 |
Rules for the implementation of electrical circuits. |
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GOST 2.705-70 |
Rules for the implementation of electrical circuits, windings and products with windings. |
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GOST 2.708-81 |
Rules for the implementation of electrical circuits of digital computers. |
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GOST 2.709-72 |
Circuit designation system in electrical circuits. |
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GOST 2.710-81 |
Alphanumeric designations in electrical circuits. |
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GOST 2.721-74 |
General use symbols. |
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GOST 2.723-68 |
Inductors, chokes, transformers, autotransformers and magnetic amplifiers. |
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GOST 2.727-68 |
Arresters, fuses. |
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GOST 2.728-74 |
Resistors, capacitors. |
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GOST 2.729-68 |
Electrical measuring instruments. |
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GOST 2.730-73 |
Semiconductor devices. |
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GOST 2.731-81 |
Electrovacuum devices. |
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GOST 2.732-68 |
Sources of light. |
