Power unit. Simple power supply 12V power supply diagram

24.06.2015

We present a powerful stabilized 12 V power supply. It is built on an LM7812 stabilizer chip and TIP2955 transistors, which provides a current of up to 30 A. Each transistor can provide a current of up to 5 A, respectively, 6 transistors will provide a current of up to 30 A. You can change the number of transistors and get desired current value. The microcircuit produces a current of about 800 mA.

A 1 A fuse is installed at its output to protect against large transient currents. It is necessary to ensure good heat dissipation from transistors and the microcircuit. When the current through the load is large, the power dissipated by each transistor also increases, so that excess heat can cause the transistor to fail.

In this case, a very large radiator or fan will be required for cooling. 100 ohm resistors are used for stability and to prevent saturation as... the gain factors have some scatter for the same type of transistors. The bridge diodes are designed for at least 100 A.

Notes

The most expensive element of the entire design is perhaps the input transformer. Instead, it is possible to use two series-connected car batteries. The voltage at the input of the stabilizer must be a few volts higher than the required output (12V) so that it can maintain a stable output. If a transformer is used, the diodes must be able to withstand a fairly large peak forward current, typically 100A or more.

No more than 1 A will pass through LM 7812, the rest is provided by transistors. Since the circuit is designed for a load of up to 30 A, six transistors are connected in parallel. The power dissipated by each of them is 1/6 of the total load, but it is still necessary to ensure sufficient heat dissipation. Maximum load current will result in maximum dissipation and will require a large heatsink.

To effectively remove heat from the radiator, it may be a good idea to use a fan or water-cooled radiator. If the power supply is loaded to its maximum load, and the power transistors fail, then all the current will pass through the chip, which will lead to a catastrophic result. To prevent breakdown of the microcircuit, there is a 1 A fuse at its output. The 400 MOhm load is for testing only and is not included in the final circuit.

Computations

This diagram is an excellent demonstration of Kirchhoff's laws. The sum of currents entering a node must be equal to the sum of currents leaving this node, and the sum of the voltage drops on all branches of any closed circuit circuit must be equal to zero. In our circuit, the input voltage is 24 volts, of which 4V drops across R7 and 20 V at the input of LM 7812, i.e. 24 -4 -20 = 0. At the output, the total load current is 30A, the regulator supplies 0.866A and 4.855A each 6 transistors: 30 = 6 * 4.855 + 0.866.

The base current is about 138 mA per transistor, to get a collector current of about 4.86A, the DC gain for each transistor must be at least 35.

TIP2955 meets these requirements. The voltage drop across R7 = 100 Ohm at maximum load will be 4V. The power dissipated on it is calculated by the formula P= (4 * 4) / 100, i.e. 0.16 W. It is desirable that this resistor be 0.5 W.

The input current of the microcircuit comes through a resistor in the emitter circuit and the B-E junction of the transistors. Let's apply Kirchhoff's laws once again. The regulator input current consists of 871 mA current flowing through the base circuit and 40.3 mA through R = 100 Ohms.
871.18 = 40.3 + 830. 88. The input current of the stabilizer must always be greater than the output current. We can see that it only consumes about 5 mA and should barely get warm.

Testing and Bugs

During the first test, there is no need to connect the load. First, we measure the output voltage with a voltmeter; it should be 12 volts, or a value not very different. Then we connect a resistance of about 100 Ohms, 3 W as a load. The voltmeter readings should not change. If you do not see 12 V, then, after turning off the power, you should check the correctness of installation and the quality of soldering.

One of the readers received 35 V at the output, instead of the stabilized 12 V. This was caused by a short circuit in the power transistor. If there is a short circuit in any of the transistors, you will have to unsolder all 6 to check the collector-emitter transitions with a multimeter.

The type of power supply, as already noted, is switching. This solution dramatically reduces the weight and size of the structure, but works no worse than the ordinary network transformer we are used to. The circuit is assembled on a powerful IR2153 driver. If the microcircuit is in a DIP package, then a diode must be installed. As for the diode, please note that it is not an ordinary one, but an ultra-fast one, since the operating frequency of the generator is tens of kilohertz and ordinary rectifier diodes will not work here.

In my case, the entire circuit was assembled in bulk, since I assembled it only to test its functionality. I barely had to adjust the circuit and it immediately started working like a Swiss watch.

Transformer— it is advisable to take a ready-made one, from a computer power supply (literally any one will do, I took a transformer with a pigtail from an ATX 350 watt power supply). At the output of the transformer, you can use a rectifier made of SCHOTTTKY diodes (can also be found in computer power supplies), or any fast and ultra-fast diodes with a current of 10 Amps or more, you can also use our KD213A.

Connect the circuit to the network through a 220 Volt 100 watt incandescent lamp; in my case, all the tests were done with a 12-220 inverter with short-circuit and overload protection, and only after fine tuning I decided to connect it to the 220 Volt network.

How should the assembled circuit work?

The keys are cold, without an output load (even with an output load of 50 watts, my keys remained icy).
The microcircuit should not overheat during operation.
Each capacitor should have a voltage of about 150 Volts, although the nominal value of this voltage may deviate by 10-15 Volts.
The circuit should operate silently.
The microcircuit's power resistor (47k) should overheat slightly during operation; a slight overheating of the snubber resistor (100 Ohm) is also possible.

The main problems that arise after assembly

Problem 1. We assembled a circuit; when connected, the control light that is connected to the output of the transformer blinks, and the circuit itself makes strange sounds.

Solution. Most likely there is not enough voltage to power the microcircuit, try reducing the resistance of the 47k resistor to 45, if that doesn’t help, then to 40 and so on (in 2-3kOhm steps) until the circuit works normally.

Problem 2. We assembled a circuit; when power is applied, nothing heats up or explodes, but the voltage and current at the transformer output are negligible (almost zero)

Solution. Replace the 400V 1uF capacitor with a 2mH inductor.

Problem 3. One of the electrolytes gets very hot.

Solution. Most likely it is not working, replace it with a new one and at the same time check the diode rectifier, maybe it is because of the non-working rectifier that the capacitor receives a change.

The switching power supply on the ir2153 can be used to power powerful, high-quality amplifiers, or used as a charger for powerful lead batteries, or as a power supply - all at your discretion.

The power of the unit can reach up to 400 watts, for this you will need to use a 450-watt ATX transformer and replace the electrolytic capacitors with 470 µF - and that’s it!

In general, you can assemble a switching power supply with your own hands for only $10-12, and that’s if you take all the components from a radio store, but every radio amateur has more than half of the radio components used in the circuit.

With the current level of development of the element base of radio-electronic components, a simple and reliable power supply with your own hands can be made very quickly and easily. This does not require high-level knowledge of electronics and electrical engineering. You will soon see this.

Making your first power source is quite an interesting and memorable event. Therefore, an important criterion here is the simplicity of the circuit, so that after assembly it immediately works without any additional settings or adjustments.

It should be noted that almost every electronic, electrical device or appliance needs power. The difference lies only in the basic parameters - the magnitude of voltage and current, the product of which gives power.

Making a power supply with your own hands is a very good first experience for novice electronics engineers, since it allows you to feel (not on yourself) the different magnitudes of currents flowing in devices.

The modern power supply market is divided into two categories: transformer-based and transformerless. The first ones are quite easy to manufacture for beginner radio amateurs. The second indisputable advantage is the relatively low level of electromagnetic radiation, and therefore interference. A significant disadvantage by modern standards is the significant weight and dimensions caused by the presence of a transformer - the heaviest and most bulky element in the circuit.

Transformerless power supplies do not have the last drawback due to the absence of a transformer. Or rather, it is there, but not in the classical presentation, but works with high-frequency voltage, which makes it possible to reduce the number of turns and the size of the magnetic circuit. As a result, the overall dimensions of the transformer are reduced. The high frequency is generated by semiconductor switches, in the process of switching on and off according to a given algorithm. As a result, strong electromagnetic interference occurs, so such sources must be shielded.

We will be assembling a transformer power supply that will never lose its relevance, since it is still used in high-end audio equipment, thanks to the minimal level of noise generated, which is very important for obtaining high-quality sound.

Design and principle of operation of the power supply

The desire to obtain a finished device as compact as possible led to the emergence of various microcircuits, inside of which there are hundreds, thousands and millions of individual electronic elements. Therefore, almost any electronic device contains a microcircuit, the standard power supply of which is 3.3 V or 5 V. Auxiliary elements can be powered from 9 V to 12 V DC. However, we know well that the outlet has an alternating voltage of 220 V with a frequency of 50 Hz. If it is applied directly to a microcircuit or any other low-voltage element, they will instantly fail.

From here it becomes clear that the main task of the mains power supply (PSU) is to reduce the voltage to an acceptable level, as well as convert (rectify) it from AC to DC. In addition, its level must remain constant regardless of fluctuations in the input (in the socket). Otherwise, the device will be unstable. Therefore, another important function of the power supply is voltage level stabilization.

In general, the structure of the power supply consists of a transformer, rectifier, filter and stabilizer.

In addition to the main components, a number of auxiliary components are also used, for example, indicator LEDs that signal the presence of supplied voltage. And if the power supply provides for its adjustment, then naturally there will be a voltmeter, and possibly also an ammeter.

Transformer

In this circuit, a transformer is used to reduce the voltage in a 220 V outlet to the required level, most often 5 V, 9 V, 12 V or 15 V. At the same time, galvanic isolation of high-voltage and low-voltage circuits is also carried out. Therefore, in any emergency situations, the voltage on the electronic device will not exceed the value of the secondary winding. Galvanic isolation also increases the safety of operating personnel. In case of touching the device, a person will not fall under the high potential of 220 V.

The design of the transformer is quite simple. It consists of a core that performs the function of a magnetic circuit, which is made of thin plates that conduct magnetic flux well, separated by a dielectric, which is a non-conductive varnish.

At least two windings are wound on the core rod. One is primary (also called network) - 220 V is supplied to it, and the second is secondary - reduced voltage is removed from it.

The operating principle of the transformer is as follows. If voltage is applied to the mains winding, then, since it is closed, alternating current will begin to flow through it. Around this current, an alternating magnetic field arises, which collects in the core and flows through it in the form of a magnetic flux. Since there is another winding on the core - the secondary one, under the influence of an alternating magnetic flux an electromotive force (EMF) is generated in it. When this winding is shorted to a load, alternating current will flow through it.

Radio amateurs in their practice most often use two types of transformers, which mainly differ in the type of core - armored and toroidal. The latter is more convenient to use in that it is quite easy to wind the required number of turns onto it, thereby obtaining the required secondary voltage, which is directly proportional to the number of turns.

The main parameters for us are two parameters of the transformer - voltage and current of the secondary winding. We will take the current value to be 1 A, since we will use zener diodes for the same value. About that a little further.

We continue to assemble the power supply with our own hands. And the next order element in the circuit is a diode bridge, also known as a semiconductor or diode rectifier. It is designed to convert the alternating voltage of the secondary winding of the transformer into direct voltage, or more precisely, into rectified pulsating voltage. This is where the name “rectifier” comes from.

There are various rectification circuits, but the bridge circuit is the most widely used. The principle of its operation is as follows. In the first half-cycle of the alternating voltage, current flows along the path through the diode VD1, resistor R1 and LED VD5. Next, the current returns to the winding through open VD2.

A reverse voltage is applied to the diodes VD3 and VD4 at this moment, so they are locked and no current flows through them (in fact, it only flows at the moment of switching, but this can be neglected).

In the next half-cycle, when the current in the secondary winding changes its direction, the opposite will happen: VD1 and VD2 will close, and VD3 and VD4 will open. In this case, the direction of current flow through resistor R1 and LED VD5 will remain the same.

A diode bridge can be soldered from four diodes connected according to the diagram above. Or you can buy it ready-made. They come in horizontal and vertical versions in different housings. But in any case, they have four conclusions. The two terminals are supplied with alternating voltage, they are designated by the sign “~”, both are the same length and are the shortest.

The rectified voltage is removed from the other two terminals. They are designated “+” and “-”. The “+” pin has the longest length among the others. And on some buildings there is a bevel near it.

Capacitor filter

After the diode bridge, the voltage has a pulsating nature and is still unsuitable for powering microcircuits, and especially microcontrollers, which are very sensitive to various kinds of voltage drops. Therefore it needs to be smoothed out. To do this, you can use a choke or a capacitor. In the circuit under consideration, it is enough to use a capacitor. However, it must have a large capacitance, so an electrolytic capacitor should be used. Such capacitors often have polarity, so it must be observed when connecting to the circuit.

The negative terminal is shorter than the positive one and a “-” sign is applied to the body near the first one.

Voltage regulator L.M. 7805, L.M. 7809, L.M. 7812

You probably noticed that the voltage in the outlet is not equal to 220 V, but varies within certain limits. This is especially noticeable when connecting a powerful load. If you do not apply special measures, then it will change in a proportional range at the output of the power supply. However, such vibrations are extremely undesirable and sometimes unacceptable for many electronic elements. Therefore, the voltage after the capacitor filter must be stabilized. Depending on the parameters of the powered device, two stabilization options are used. In the first case, a zener diode is used, and in the second, an integrated voltage stabilizer is used. Let's consider the application of the latter.

In amateur radio practice, voltage stabilizers of the LM78xx and LM79xx series are widely used. Two letters indicate the manufacturer. Therefore, instead of LM there may be other letters, for example CM. The marking consists of four numbers. The first two - 78 or 79 - mean positive or negative voltage, respectively. The last two digits, in this case instead of two X's: xx, indicate the value of the output U. For example, if the position of two X's is 12, then this stabilizer produces 12 V; 08 – 8 V, etc.

For example, let's decipher the following markings:

LM7805 → 5V positive voltage

LM7912 → 12 V negative U

Integrated stabilizers have three outputs: input, common and output; designed for current 1A.

If the output U significantly exceeds the input and the maximum current consumption is 1 A, then the stabilizer gets very hot, so it should be installed on a radiator. The design of the case provides for this possibility.

If the load current is much lower than the limit, then you don’t have to install a radiator.

The classic design of the power supply circuit includes: a network transformer, a diode bridge, a capacitor filter, a stabilizer and an LED. The latter acts as an indicator and is connected through a current-limiting resistor.

Since in this circuit the current-limiting element is the LM7805 stabilizer (allowable value 1 A), all other components must be rated for a current of at least 1 A. Therefore, the secondary winding of the transformer is selected for a current of one ampere. Its voltage should not be lower than the stabilized value. And for good reason, it should be chosen from such considerations that after rectification and smoothing, U should be 2 - 3 V higher than the stabilized one, i.e. A couple of volts more than its output value should be supplied to the input of the stabilizer. Otherwise it will not work correctly. For example, for LM7805 input U = 7 - 8 V; for LM7805 → 15 V. However, it should be taken into account that if the value of U is too high, the microcircuit will heat up very much, since the “excess” voltage is extinguished at its internal resistance.

The diode bridge can be made from 1N4007 type diodes, or take a ready-made one for a current of at least 1 A.

Smoothing capacitor C1 should have a large capacity of 100 - 1000 µF and U = 16 V.

Capacitors C2 and C3 are designed to smooth out high-frequency ripple that occurs when the LM7805 operates. They are installed for greater reliability and are recommendations from manufacturers of stabilizers of similar types. The circuit also works normally without such capacitors, but since they cost practically nothing, it is better to install them.

DIY power supply for 78 L 05, 78 L 12, 79 L 05, 79 L 08

Often it is necessary to power only one or a pair of microcircuits or low-power transistors. In this case, it is not rational to use a powerful power supply. Therefore, the best option would be to use stabilizers of the 78L05, 78L12, 79L05, 79L08, etc. series. They are designed for a maximum current of 100 mA = 0.1 A, but are very compact and no larger in size than a regular transistor, and also do not require installation on a radiator.

The markings and connection diagram are similar to the LM series discussed above, only the location of the pins differs.

For example, the connection diagram for the 78L05 stabilizer is shown. It is also suitable for LM7805.

The connection diagram for negative voltage stabilizers is shown below. The input is -8 V, and the output is -5 V.

As you can see, making a power supply with your own hands is very simple. Any voltage can be obtained by installing an appropriate stabilizer. You should also remember the transformer parameters. Next we will look at how to make a power supply with voltage regulation.

How to assemble a simple power supply and a powerful voltage source yourself.
Sometimes you have to connect various electronic devices, including homemade ones, to a 12 volt DC source. The power supply is easy to assemble yourself within half a weekend. Therefore, there is no need to purchase a ready-made unit, when it is more interesting to independently make the necessary thing for your laboratory.

Anyone who wants to can make a 12-volt unit on their own, without much difficulty.
Some people need a source to power an amplifier, while others need a source to power a small TV or radio...
Step 1: What parts are needed to assemble the power supply...
To assemble the block, prepare in advance the electronic components, parts and accessories from which the block itself will be assembled....
-Circuit board.
-Four 1N4001 diodes, or similar. Diode bridge.
- Voltage stabilizer LM7812.
-Low-power step-down transformer for 220 V, the secondary winding should have 14V - 35V alternating voltage, with a load current from 100 mA to 1A, depending on how much power is needed at the output.
-Electrolytic capacitor with a capacity of 1000 µF - 4700 µF.
-Capacitor with a capacity of 1uF.
-Two 100nF capacitors.
-Cuttings of installation wire.
-Radiator, if necessary.
If you need to get maximum power from the power source, you need to prepare an appropriate transformer, diodes and a heatsink for the chip.
Step 2: Tools....
To make a block, you need the following installation tools:
-Soldering iron or soldering station
-Pliers
-Installation tweezers
- Wire strippers
-Device for solder suction.
-Screwdriver.
And other tools that may be useful.
Step 3: Diagram and others...

To obtain 5 volt stabilized power, you can replace the LM7812 stabilizer with an LM7805.
To increase the load capacity to more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail due to overheating.
However, if you need to get several hundred milliamps (less than 500 mA) from the source, then you can do without a radiator, the heating will be negligible.
In addition, an LED has been added to the circuit to visually verify that the power supply is working, but you can do without it.

Power supply circuit 12V 30A.
When using one 7812 stabilizer as a voltage regulator and several powerful transistors, this power supply is capable of providing an output load current of up to 30 amperes.
Perhaps the most expensive part of this circuit is the power step-down transformer. The voltage of the secondary winding of the transformer must be several volts higher than the stabilized voltage of 12V to ensure the operation of the microcircuit. It must be borne in mind that you should not strive for a larger difference between the input and output voltage values, since at such a current the heat sink of the output transistors increases significantly in size.
In the transformer circuit, the diodes used must be designed for a high maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not be more than 1A.
Six composite Darlington transistors of the TIP2955 type connected in parallel provide a load current of 30A (each transistor is designed for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you turn it on for the first time, it is not recommended to connect a load. We check the functionality of the circuit: connect a voltmeter to the output terminals and measure the voltage, it should be 12 volts, or the value is very close to it. Next, we connect a 100 Ohm load resistor with a dissipation power of 3 W, or a similar load - such as an incandescent lamp from a car. In this case, the voltmeter reading should not change. If there is no 12 volt voltage at the output, turn off the power and check the correct installation and serviceability of the elements.
Before installation, check the serviceability of the power transistors, since if the transistor is broken, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check the power transistors for short circuits; to do this, use a multimeter to separately measure the resistance between the collector and emitter of the transistors. This check must be carried out before installing them in the circuit.

Power supply 3 - 24V

The power supply circuit produces an adjustable voltage in the range from 3 to 25 volts, with a maximum load current of up to 2A; if you reduce the current-limiting resistor to 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding radiators; the power of the limiting resistor must be at least 3 W. Voltage regulation is controlled by an LM1558 or 1458 op amp. When using a 1458 op amp, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to 3 of the op amp from a divider on resistors rated 5.1 K.
The maximum DC voltage for powering op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must produce a voltage at least 4 volts higher than the stabilized output voltage. The power transformer in the circuit has an output voltage of 25.2 volts AC with a tap in the middle. When switching windings, the output voltage decreases to 15 volts.

1.5 V power supply circuit

The power supply circuit to obtain a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.

Diagram of an adjustable power supply from 1.5 to 12.5 V

Power supply circuit with output voltage regulation to obtain voltage from 1.5 volts to 12.5 volts; the LM317 microcircuit is used as a regulating element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the housing.

Power supply circuit with fixed output voltage

Power supply circuit with a fixed output voltage of 5 volts or 12 volts. The LM 7805 chip is used as an active element, LM7812 is installed on a radiator to cool the heating of the case. The choice of transformer is shown on the left on the plate. By analogy, you can make a power supply for other output voltages.

20 Watt power supply circuit with protection

The circuit is intended for a small homemade transceiver, author DL6GL. When developing the unit, the goal was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, maximum 15V, for a load current of 2.7A.
Which scheme: switching power supply or linear?
Switching power supplies are small-sized and have good efficiency, but it is unknown how they will behave in a critical situation, surges in the output voltage...
Despite the shortcomings, a linear control scheme was chosen: a fairly large transformer, not high efficiency, cooling required, etc.
Parts from a homemade power supply from the 1980s were used: a radiator with two 2N3055. The only thing missing was a µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a µA723/LM723 microcircuit with standard inclusion. Output transistors T2, T3 type 2N3055 are installed on radiators for cooling. Using potentiometer R1, the output voltage is set within 12-15V. Using variable resistor R2, the maximum voltage drop across resistor R7 is set, which is 0.7V (between pins 2 and 3 of the microcircuit).
A toroidal transformer is used for the power supply (can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (surge) at the output of the power supply is exceeded, by adjusting R3 the voltage threshold is set on leg 2 from the divider R3/R8/R9 (2.6V reference voltage), the voltage that opens the thyristor BT145 is supplied from output 8, causing a short circuit leading to tripping of fuse 6.3a.

To prepare the power supply for operation (the 6.3A fuse is not yet involved), set the output voltage to, for example, 12.0V. Load the unit with a load; for this you can connect a 12V/20W halogen lamp. Set R2 so that the voltage drop is 0.7V (the current should be within 3.8A 0.7=0.185Ωx3.8).
We configure the operation of the overvoltage protection; to do this, we smoothly set the output voltage to 16V and adjust R3 to trigger the protection. Next, we set the output voltage to normal and install the fuse (before that we installed a jumper).
The described power supply can be reconstructed for more powerful loads; to do this, install a more powerful transformer, additional transistors, wiring elements, and a rectifier at your discretion.

Homemade 3.3v power supply

If you need a powerful power supply of 3.3 volts, then it can be made by converting an old power supply from a PC or using the above circuits. For example, replace a 47 ohm resistor of a higher value in the 1.5 V power supply circuit, or install a potentiometer for convenience, adjusting it to the desired voltage.

Transformer power supply on KT808

Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully used and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that is floating around the Internet. Many spears and arrows have been broken on forums when discussing what is better, a field-effect transistor or a regular silicon or germanium one, what temperature of crystal heating will they withstand and which one is more reliable?
Each side has its own arguments, but you can get the parts and make another simple and reliable power supply. The circuit is very simple, protected from overcurrent, and when three KT808 are connected in parallel, it can produce a current of 20A; the author used such a unit with 7 parallel transistors and delivered 50A to the load, while the filter capacitor capacity was 120,000 uF, the voltage of the secondary winding was 19V. It must be taken into account that the relay contacts must switch such a large current.

If installed correctly, the output voltage drop does not exceed 0.1 volt

Power supply for 1000V, 2000V, 3000V

If we need to have a high voltage DC source to power the transmitter output stage lamp, what should we use for this? On the Internet there are many different power supply circuits for 600V, 1000V, 2000V, 3000V.
First: for high voltage, circuits with transformers for both one phase and three phases are used (if there is a three-phase voltage source in the house).
Second: to reduce size and weight, they use a transformerless power supply circuit, directly a 220-volt network with voltage multiplication. The biggest drawback of this circuit is that there is no galvanic isolation between the network and the load, as the output is connected to a given voltage source, observing phase and zero.

The circuit has a step-up anode transformer T1 (for the required power, for example 2500 VA, 2400V, current 0.8 A) and a step-down filament transformer T2 - TN-46, TN-36, etc. To eliminate current surges during switching on and protection diodes when charging capacitors, switching is used through quenching resistors R21 and R22.
The diodes in the high-voltage circuit are shunted by resistors in order to uniformly distribute Urev. Calculation of the nominal value using the formula R(Ohm) = PIVx500. C1-C20 to eliminate white noise and reduce surge voltages. You can also use bridges like KBU-810 as diodes by connecting them according to the specified circuit and, accordingly, taking the required amount, not forgetting about shunting.
R23-R26 for discharging capacitors after a power outage. To equalize the voltage on series-connected capacitors, equalizing resistors are placed in parallel, which are calculated from the ratio for every 1 volt there are 100 ohms, but at high voltage the resistors turn out to be quite powerful and here you have to maneuver, taking into account that the open-circuit voltage is higher by 1, 41.

Stages of preliminary work: preparing for construction

Before you start remaking the battery, select another power supply unit that is suitable in size, then it must be placed in the existing case and secured. Everything is removed from the inside of the prepared device and the internal space is measured, which differs from the external contents.

What you need to know before starting construction

Study the markings or design features indicated on the body of the working tool, and, based on these indicators, determine the voltage required for power supply. In our case, it will be enough to assemble a 12V power supply for a screwdriver with your own hands. If the required ratings are other than 12V, continue to look for an interchangeable option. Having chosen an analogue, calculate the current consumption of the screwdriver, since the manufacturer does not indicate this parameter. To find out, you will need to know the power of the device.

If you don’t have time to select a device, and the calculations take too much time, take any power supply you come across. When buying it, in addition to the current, ask about the battery capacity. To construct a 12V power supply for a screwdriver with your own hands, a device with a capacity of 1.2A and a charge of 2.5 will be sufficient. Remember, before looking for recharging, determine the following necessary parameters:

Block dimensions.
Minimum current.
Required voltage level.

The process of designing a battery pack for a screwdriver

Having selected a new device and all the parts necessary for design, you can begin to work. Assembling a 12V power supply for a screwdriver with your own hands consists of the following steps:

Having selected the optimal power supply, check it for similarity with the declared characteristics, which will depend on which screwdriver. It is better to use a computer block as the basis for a new battery.
Disassemble the screwdriver and remove the old drive. If the body is glued, gently tap along the seam with a hammer or score using a thin knife blade. This way you will open the box with the least damage.
Unsolder the cord and leads from the plug and separate them from the rest of the structure.
In the place where the battery power supply for the screwdriver was previously located, place the other contents removed from the case.
Lead the power cord through the opening in the housing. Connect it to the power supply by soldering it in place.
Use soldering to connect the output of the computer power supply to the battery terminals. Remember to maintain polarity.
Connect the designed battery to the device and test it.
If the dimensions of the new charger exceed those of the old battery, it can be built inside the screwdriver handle.
To limit the supply of voltage from the network to the battery with a parallel supply output, install a diode with the required power from inside the “+” cable break between the battery socket, including the output, but with the “-” pole towards the engine.

What does this battery upgrade give?

Transforming the power supply for a computer into a battery for a screwdriver operating continuously from the mains has a number of advantages, namely:

There is no need to worry about periodically recharging the device.
Downtime during long periods of operation is reduced to a minimum.
The torque remains constant thanks to the constant current supply.
Connecting a converted computer power supply for a screwdriver (12V) does not in any way affect the technical parameters of the product, even if the device has not been used for a long period of time.

The only quality that is mentioned as a disadvantage is the presence of an electrical outlet near the work site. This problem can be easily solved by connecting an extension cord.

Materials and working tools for upgrading a screwdriver

Remaking a computer power supply for a screwdriver is not difficult; moreover, such an activity is educational, especially for beginners in the field of radio mechanics. Having the necessary skills and all the components, in a short time you will have a transformed corded screwdriver. To carry out the work you will need:

charger from a screwdriver;
old factory battery;
soft multi-core electrical cable;
soldering iron and solder;
acids;
insulating tape;
power supply from a computer (or another).

Transformation options

You can use various power supply options to create a compact battery for uninterrupted operation of the screwdriver.

Battery or power supply from computer equipment

A device that supports the charge of a PC or laptop is quite suitable for achieving this goal. The process of introducing a power supply into a screwdriver is as follows:

The screwdriver body is completely disassembled.
The old power supply is removed and the wires are unsoldered.
The wiring of the new unit is connected to the wiring of the old one, which powers the previous battery. When carrying out such an operation, it is important to observe polarity!
Turn on the screwdriver and check for functionality. If all wires are connected correctly, the machine will work.
There is a hole in the body of the device where a plug with a charging connector can easily be placed. By upgrading a screwdriver in this way, you get an improved device, which is now also recharged during operation like a laptop from a 220V network.
The new power source is mounted inside the screwdriver, securing it with glue.
The remaining body elements are returned to their place and the product is twisted, giving it its original appearance.

That's all! Now you know how to turn a cordless screwdriver into a corded one.

Car battery as a power source

A car battery is an excellent option for remotely connecting a screwdriver to the network. To implement the idea, simply disconnect the clamps from the working tool and connect it to a power source.

Important! The use of such a source for long-term operation of a screwdriver is highly not recommended.

Using a welding inverter to power a screwdriver

To remake the old design, prepare a power supply circuit for a 12V screwdriver. The old design is improved to some extent by adding a secondary coil.

When compared with a computer battery, the advantage of the inverter is immediately noticeable. Thanks to the design features, it is immediately possible to determine the required voltage level and output current. This is an ideal method for those who live in radio engineering.

Features of corded screwdrivers

You can transform the device into a network device using another method, based on the production of a mobile station for recharging a screwdriver. An elastic wire is connected to the unit, to one end of which a plug is attached. Although, in order to operate such a station, you will need to build a special power supply or connect a ready-made transformer with a rectifier.

Important! Do not forget to ensure that the characteristics of the transformer match the parameters of the instrument.

If you are new to this business, then most likely it will be difficult for you to transform the coil with your own hands. Without having important skills, you can make a mistake with the number of turns or selection of wire diameter, so it is better to entrust such work to a specialist or at least a person who understands the topic.

90% of equipment is sold with a built-in transformer. All you need to do is select the best option and design a rectifier for it. To solder the rectifier bridge, semiconductor diodes are used, selected strictly according to the parameters of the tool.

Experts recommend following certain rules to everyone who decides to reconstruct a screwdriver and construct a 12V power supply for a screwdriver with their own hands. Instructions for upgrading the tool include the following tips:

You can use a corded screwdriver as much as you like without worrying about the battery running out. However, such an instrument needs rest. Therefore, take five-minute breaks to avoid overheating or overloading the instrument.
When working with a screwdriver, do not forget to secure the wire in the elbow area. This will make it more convenient to operate the device, and the cord will not interfere when screwing in screws.
Carry out systematic cleaning of the screwdriver power supply from accumulations of dust and dirt deposits.
The new battery is provided with grounding.
Do not use more than one extension cord to connect to the network.
This device is not recommended for use in high-altitude work (from two meters).

Now you know what power supply is needed for a 12V screwdriver, and what materials to use to make such a design yourself at home. There is no need to replace the old screwdriver with a new one. A radical decision should be made only if the unit is completely out of order, and a “dead” battery is not a problem for the craftsman. You just need to have an understanding of radio engineering and arm yourself with a soldering iron. Then it will be easier to cope with the task.