Or how to make a cheap power supply for a 100W amplifier
And how much will a ULF watt for 300 cost?
Looking for what :)
Listen at home!
Bucks *** will be normal ...
Omg! How about cheaper?
Mmmmm... I have to think...
And I remembered about a pulsed power supply unit, powerful enough and reliable for ULF.
And I began to think about how to remake it for our needs :)
After some negotiations, the person for whom all this was conceived lowered the power bar from 300 watts to 100-150, agreed to take pity on the neighbors. Accordingly, a 200 W pulse will be more than enough.
As you know, an ATX format computer power supply gives us 12, 5 and 3.3 V. In AT power supplies there was also a voltage of "-5 V". We don't need these pressures.
In the first PSU that came across, which was opened for alteration, there was a PWM chip, beloved by the people, - TL494.
This power supply was an ATX 200 W company, I don’t remember which one. It doesn't really matter. Since the comrade was "burning", the ULF cascade was simply bought. It was a mono amplifier on a TDA7294 that can deliver 100 watts peak, which is fine. The amplifier required a bipolar supply + -40V.
We remove everything superfluous and unnecessary in the decoupled (cold) part of the PSU, leaving the pulse shaper and the OS circuit. We put Schottky diodes more powerful and at a higher voltage (in the converted power supply they were 100 V). We also put electrolytic capacitors in voltage exceeding the required voltage by 10-20 volts for a reserve. Fortunately, there is a place where to roam.
Look at the photo with caution: not all elements are standing :)
Now the main "part to be reworked" is the transformer. There are two options:
- disassemble and rewind for specific voltages;
- solder the windings in series, adjusting the output voltage using PWM
I did not bother and chose the second option.
We disassemble it and solder the windings in series, not forgetting to make a midpoint:
To do this, the transformer leads were disconnected, ringed and twisted in series.
In order to see whether I made a mistake with the winding when connected in series or not, I started pulses with a generator and looked at what was obtained at the output with an oscilloscope.
At the end of these manipulations, I connected all the windings and made sure that from the midpoint they have the same voltage.
We put it in place, calculate the OS circuit on the TL494 at 2.5V from the output of the voltage divider to the second leg and turn it on in series through a 100W lamp. If everything works well - add one more garland to the chain, and then another one hundred-watt lamp. For insurance against unfortunate scattering of parts :)
Lamp as a fuse
The lamp should blink and go out. It is highly desirable to have an oscilloscope in order to be able to see what is happening on the microcircuit and buildup transistors.
Along the way, for those who do not know how to use datasheets, we are learning. Datasheet and Google help forums better if you have advanced skills in "google" and "translator with an alternative point of view."
I found an approximate power supply circuit on the Internet. The scheme is very simple (both schemes can be saved in good quality):
In the end, it turned out something like this, but this is a very rough approximation, a lot of details are missing!
The design of the speaker was coordinated and paired with the power supply and amplifier. It turned out nice and simple:
On the right, under a cut-off heatsink for a video card and a computer cooler, there is an amplifier; on the left, its power supply. The power supply unit gave out stabilized voltages + -40 V from the positive voltage side. The load was something around 3.8 ohms (there are two speakers in the column). Fits compactly and works great!
The presentation of the material is not complete enough, I missed a lot of points, since it was a few years ago. As an aid to repetition, I can recommend circuits from powerful low-frequency car amplifiers - there are bipolar converters, as a rule, on the same chip - tl494.
Photo of the happy owner of this device :)
He holds this column so symbolically, almost like an AK-47 assault rifle ... He feels reliable and will soon leave for the army :)
We remind you that you can also find us in the Vkontakte group, where every question will definitely be answered!
There is a lot of information on the Internet about converting ATX-AT computer power supplies into laboratory power supplies and chargers. I re-read more than a dozen articles about rework, but there is practically no information about self-assembly from the details of these same PSU PCs. Why is this so, because ATX is an excellent donor for a good power supply, and if it is assembled on some kind of left PWM, it can always be replaced with TL494, on a brand new neat board. And most importantly, your pay
My ATX 400W power supply burned out. I added him to five more brothers, I realized that I had to do something with them. I decided to start with the extreme 400W Bp, I was attracted to it by two 12V 12A and 15A buses, which in total gave 27A. But it turned out that both buses are connected to the same 12V output and it’s unlikely that the necessary Amperes will be collected there. But maybe I’ll squeeze out at least 20A, I thought and decided to assemble the power supply.
Assembly conditions:
- make AT from ATX
- universal board for further improvements
- minimum details
- PWM only TL494
- voltage stabilization 12V, 14.4V and current up to 20A
Having searched for AT power supply circuit diagrams in tyrnet, I chose the circuit and redid it a bit
Didn't do anything special to the block.
- Excluded extra strapping 5V 3.3V, etc.
- Reworked the divider circuits around the TL494 error comparators. Added the ability to: switch voltages 12.6V and 14.4V, smoothly adjust the load current
- Well, in general, I transferred ATX to 3528, to AT on TL494. One thing did not give rest, at what frequency the donor worked. But then it turned out that the frequency calculation formula for 3528 is the same as for TL494 F=1.1/RC. According to the scheme, the frequency is 73 kHz
Started making payments. After hours of torment, such a payment turned out.
Fee for this moment final and never in the assembly was not. The first version of the board is slightly lighter, there are no circuits around the error amplifiers, but the control is carried out from another board through an optocoupler transistor from 14 Vref to 4 leg DT. The second version eliminates the optocoupler and control is carried out through dividers on an additional board, through the legs TL494 1,2,3,15,16. The first and second versions of the power supply board are working and one hundred percent tested. So be careful, check new version boards before manufacturing. If there are errors, write through the form, I will correct everything.
And a few words about the launch. passed according to tradition through an incandescent light bulb, everything worked. The output without stabilization turned out to be 19V. The next start was through a fuse, 24.2V appeared at the output. I connected 4.2A 24V lamps from the car to the load. Voltage dipped by 0.2V
When the stabilization of 14.4V was connected to the load, it gave 8.4A, the voltage dipped by 0.2V. Unfortunately I didn't take a photo.
It also reacts normally to current limiting. More than 10A has not yet loaded, Nothing. No photo yet
Well, a couple more photos of the assembled board before the first tests
Video of the assembled power supply-charger from ATX
That's all for now. More photos and updates as time goes by
With uv. Admin check
I needed a lightweight power supply, for different things (expeditions, power supply of various HF and VHF transceivers or in order not to carry a transformer power supply unit when moving to another apartment). After reading the available information on the network about the alteration of computer power supplies, I realized that I would have to figure it out myself. Everything I found was described somehow chaotically and not entirely clear (for me). Here I will tell you, in order, how I redid several different blocks. The differences will be described separately. So, I found some PSUs from old PC386 200W (at least that's what it says on the cover). Usually on the cases of such PSUs they write something like this: +5V/20A , -5V/500mA , +12V/8A , -12V/500mA
The currents indicated on the +5 and +12V buses are pulsed. It is impossible to constantly load the PSU with such currents, high-voltage transistors will overheat and crack. Subtract 25% from the maximum pulse current and get the current that the PSU can keep constantly, in this case it is 10A and up to 14-16A for a short time (no more than 20sec). Actually, here it is necessary to clarify that 200W PSUs are different, of those that I came across, not everyone could hold 20A even for a short time! Many pulled only 15A, and some up to 10A. Keep that in mind!
I want to note that specific model The power supply does not play a role, since they are all made almost according to the same scheme with slight variations. The most critical point is the presence of the DBL494 chip or its analogues. I came across a PSU with one 494 chip and with two 7500 and 339 chips. Everything else has no of great importance. If you have the opportunity to choose a PSU from several, first of all, pay attention to the size of the pulse transformer (the bigger, the better) and the presence of a network filter. It’s good when the surge protector is already soldered, otherwise you will have to unsolder it yourself in order to reduce interference. It's easy, wind 10 turns on a ferrite ring and put two capacitors, places for these parts are already provided on the board.
PRIORITY MODIFICATIONS
First, let's do a few simple things, after which you will get a well-functioning power supply with an output voltage of 13.8V, direct current up to 4 - 8A and short-term up to 12A. You will make sure that the PSU is working and decide whether you need to continue the modifications.
1. We disassemble the power supply and pull out the board from the case and carefully clean it with a brush and a vacuum cleaner. There should be no dust. After that, we solder all the bundles of wires going to the +12, -12, +5 and -5V buses.
2.
you need to find (on board) chip DBL494 (in other boards it costs 7500, this is an analogue), switch the protection priority from the + 5V bus to + 12V and set the voltage we need (13 - 14V).
Two resistors depart from the 1st leg of the DBL494 chip (sometimes more, but it doesn't matter), one goes to the body, the other to the + 5V bus. We need him, carefully solder one of his legs (break connection).
3. Now, between the + 12V bus and the first DBL494 foot microcircuit, we solder a resistor 18 - 33 kΩ. You can put a trimmer, set the voltage to + 14V and then replace it with a constant one. I recommend setting it to 14.0V rather than 13.8V, because most proprietary HF-VHF equipment works better at this voltage.
SETUP AND ADJUSTMENT
1. It's time to turn on our PSU to check if we did everything right. The fan can not be connected and the board itself can not be inserted into the case. We turn on the PSU, without load, connect a voltmeter to the + 12V bus and see what voltage it is. With a trimming resistor, which stands between the first leg of the DBL494 chip and the + 12V bus, we set the voltage from 13.9 to + 14.0V.
2. Now check the voltage between the first and seventh legs of the DBL494 chip, it should be at least 2V and not more than 3V. If this is not the case, select a resistor between the first leg and the body and the first leg and the +12V rail. Pay special attention to this item, it is key moment. If the voltage is higher or lower than the specified one, the power supply will work worse, be unstable, and keep a smaller load.
3. Short the +12V bus to the case with a thin wire, the voltage must disappear in order for it to recover - turn off the PSU for a couple of minutes (need to empty the tanks) and turn it on again. Has there been tension? Fine! As you can see, the protection works. What didn't work?! Then we throw out this PSU, it does not suit us and take another ... hee.
So, the first stage can be considered completed. Insert the board into the case, bring out the terminals for connecting the radio station. You can use the power supply! Connect the transceiver, but it is not yet possible to give a load of more than 12A! Vehicle VHF station, will operate at full power (50W), and in the HF transceiver you will have to install 40-60% of the power. What happens if you load the PSU with a large current? It's okay, protection usually works and the output voltage disappears. If the protection does not work, the high-voltage transistors will overheat and burst. In this case, the voltage will simply disappear and there will be no consequences for the equipment. After replacing them, the PSU is working again!
1. We turn the fan on the contrary, it should blow inside the case. Under the two screws of the fan, we put washers to turn it around a little, otherwise it blows only on high-voltage transistors, this is wrong, it is necessary that the air flow be directed both to the diode assemblies and to the ferrite ring.
Before this, it is advisable to lubricate the fan. If it makes a lot of noise, put a 60 - 150 ohm 2W resistor in series with it. or make a rotation regulator depending on the heating of the radiators, but more on that below.
2. Remove two terminals from the PSU to connect the transceiver. From the 12V bus to the terminal, run 5 wires from the bundle that you soldered at the beginning. Between the terminals, put a non-polar capacitor of 1 microfarad and an LED with a resistor. Negative wire, also bring to the terminal with five wires.
In some power supplies, in parallel with the terminals to which the transceiver is connected, put a resistor with a resistance of 300 - 560 ohms. This is a load so that the protection does not work. The output circuit should look something like the one shown in the diagram.
3. Power up the +12V bus and get rid of excess rubbish. Instead of a diode assembly or two diodes (which are often put in place of it), we put the assembly 40CPQ060, 30CPQ045 or 30CTQ060, any other options will worsen the efficiency. Nearby, on this radiator, there is a 5V assembly, we unsolder it and throw it away.
Under load, the following parts heat up most strongly: two radiators, pulse transformer, choke on a ferrite ring, choke on a ferrite rod. Now our task is to reduce heat transfer and increase the maximum load current. As I said earlier, it can go up to 16A (for 200W PSU).
4. Solder the choke on the ferrite rod from the + 5V bus and put it on the + 12V bus, the choke standing there earlier (it is taller and wound with a thin wire) solder and discard. Now the throttle will practically not heat up or will, but not so much. There are simply no chokes on some boards, you can do without it, but it is desirable that it be for better filtering of possible interference.
5. A choke is wound on a large ferrite ring to filter out impulse noise. The + 12V bus on it is wound with a thinner wire, and the + 5V bus is the thickest. Solder this ring carefully and swap the windings for the + 12V and + 5V buses (or turn on all windings in parallel). Now the + 12V bus passes through this inductor, with the thickest wire. As a result, this inductor will heat up much less.
6. The PSU has two radiators, one for high-power high-voltage transistors, the other for +5 and +12V diode assemblies. I came across several varieties of radiators. If, in your PSU, the dimensions of both radiators are 55x53x2mm and they have fins in the upper part (as in the photo) - you can count on 15A. When radiators are smaller size- It is not recommended to load the PSU with a current of more than 10A. When the radiators are thicker and have an additional platform in the upper part, you are in luck, this the best option, you can get 20A within a minute. If the heatsinks are small, to improve heat dissipation, you can attach a small plate of duralumin or a half from the heatsink of an old processor to them. Pay attention to whether the high-voltage transistors are well screwed to the radiator, sometimes they hang out.
7. We solder the electrolytic capacitors on the + 12V bus, put 4700x25V in their place. It is advisable to unsolder the capacitors on the + 5V bus, just so that there is more free space and the air from the fan blows the parts better.
8. On the board you see two high voltage electrolytes, usually 220x200V. Replace them with two 680x350V, in extreme cases, connect two 220+220=440mKf in parallel. This is important, and the point here is not only filtering, impulse noise will be weakened and resistance to maximum loads. The result can be viewed with an oscilloscope. In general, it is necessary to do it!
9. It is desirable that the fan changes speed depending on the heating of the PSU and does not spin when there is no load. This will extend the life of the fan and reduce noise. I offer two simple and reliable schemes. If you have a thermistor, look at the circuit in the middle, set the temperature of the thermistor response to about + 40C with a trimmer resistor. Transistor, it is necessary to install KT503 with maximum current gain (this is important), other types of transistors work worse. A thermistor of any type is NTC, which means that when heated, its resistance should decrease. You can use a thermistor with a different rating. The tuning resistor should be multi-turn, so it is easier and more accurate to adjust the temperature of the fan operation. We fasten the board with the circuit to the free ear of the fan. We attach the thermistor to the throttle on the ferrite ring, it heats up faster and stronger than other parts. You can glue the thermistor to the 12V diode assembly. It is important that none of the thermistor leads short to the radiator!!! In some PSUs, there are fans with a high current consumption, in this case, after KT503, you need to put KT815.
If you don’t have a thermistor, make a second circuit, see on the right, it uses two D9 diodes as a thermocouple. Glue them with transparent flasks to the radiator on which the diode assembly is installed. Depending on the transistors used, sometimes you need to choose a 75 kΩ resistor. When the PSU is running without load, the fan should not spin. Everything is simple and reliable!
CONCLUSION
From computer block 200W power supply, really get 10 - 12A (if the PSU will have large transformers and radiators) at a constant load and 16 - 18A for a short time at an output voltage of 14.0V. This means you can operate SSB and CW at full power with ease. (100W) transceiver. In SSTV, RTTY, MT63, MFSK and PSK modes, you will have to reduce the transmitter power to 30-70W, depending on the duration of the transmission.
The weight of the converted PSU is approximately 550g. It is convenient to take it with you on radio expeditions and various trips.
When writing this article and during the experiments, three PSUs were damaged (as you know, experience does not come immediately) and successfully redone five power supplies.
A big plus of a computer PSU is that it works stably when the mains voltage changes from 180 to 250V. Some instances work with a larger voltage spread.
See photos of successfully converted switching power supplies:
Igor Lavrushov
Kislovodsk
The computer serves us for years, becomes a real friend of the family, and when it becomes obsolete or hopelessly breaks down, it can be so pitiful to carry it to a landfill. But there are details that can last a long time in everyday life. This and
numerous coolers, and a processor heatsink, and even the case itself. But the most valuable thing is BP. due to decent power with small dimensions, it is an ideal object for all sorts of upgrades. Its transformation is not such a difficult task.
Converting a computer into a conventional voltage source
You need to decide what type of power supply your computer has, AT or ATX. As a rule, this is indicated on the case. Switching power supplies only work under load. But the device of the ATX type power supply allows you to artificially imitate it by shorting the green and black wires. So, by connecting the load (for AT) or closing the necessary outputs (for ATX), you can start the fan. The output appears 5 and 12 volts. The maximum output current depends on the power of the PSU. At 200 W, at a five-volt output, the current can reach about 20A, at 12V - about 8A. So at no extra cost, you can use a good one with good output characteristics.
Converting a computer power supply into an adjustable voltage source
Having such a PSU at home or at work is quite convenient. Modifying a building block is easy. It is necessary to replace several resistances and unsolder the inductor. In this case, the voltage can be adjusted from 0 to 20 volts. Naturally, the currents will remain in their original proportions. If you are satisfied with the maximum voltage of 12V, it is enough to install a thyristor voltage regulator at its output. The controller circuit is very simple. At the same time, it will help to avoid interference with the internal part of the computer unit.
Converting a computer power supply into a car charger
The principle is not much different from a regulated power supply. It is only desirable to change to more powerful ones. A charger from a computer power supply has a number of advantages and disadvantages. The advantages are primarily small dimensions and light weight. Transformer memory is much heavier and more inconvenient to use. The disadvantages are also significant: criticality to short circuits and polarity reversal.
Of course, this criticality is also observed in transformer devices, but when the pulse unit fails, alternating current with a voltage of 220V tends to the battery. It is terrible to imagine the consequences of this for all devices and people nearby. The use of protection in power supplies solves this problem.
Before using such charger, take seriously the manufacture of the protection circuit. Moreover, there is a large number of their varieties.
So, do not rush to throw away spare parts from the old device. Reworking a computer power supply will give it a second life. When working with a PSU, remember that its board is constantly energized with 220V, and this is a mortal threat. Observe personal safety rules when working with electric current.
In the article, you will learn how to make a laboratory power supply yourself from what is at hand. To date, there are quite a few devices that need different power - and 5, and 3, and 12 volts. And some even feed on high-frequency current (these devices will be discussed separately). But it’s worth starting with the classic circuit - on a transformer. Of course, the design will turn out to be cumbersome, and the circuit is outdated, but the reliability is high.
Power Supply Transformer
For a laboratory power supply, it is necessary to use transformers of the TC-270 type (two-coil, from old tube color TVs). But they will have to be slightly modernized. The primary windings remain in place, the secondary windings are completely removed. This is how a laboratory power supply is made, the circuit of which is given in the article. New windings are wound based on existing needs. The easiest option is to make step voltage regulation at the output. To do this, you need to calculate how many turns are needed to remove one Volt:
- You wind 10 turns of wire instead of the secondary winding.
- Turn on the transformer and measure the voltage on the secondary winding.
- Let's say it turned out 2 V. Therefore, 5 turns give out 1 V.
- To make "steps" of 1 V, you need to make taps every five turns.
Such a design will be massive, and you will have to use either several sockets or a special toggle switch to switch operating modes. It will be much easier to wind the secondary winding so that the output is approximately 30 volts of alternating voltage.
Voltage regulation
Above was an example of step adjustment. But the laboratory power supply, the circuit of which is given in the article, has one big advantage - the secondary winding in it is solid, without taps. Adjustment is carried out using a special circuit on semiconductor elements. With the help of a variable resistor, the parameters of the semiconductor junction are changed. As a result, the parameters of the circuit and the output voltage change.
The fact is that you get an adjustable laboratory power supply. And in order to control the output voltage, you will need to connect a voltmeter to it. The easiest way is to use the arrow, the main thing is that the scale is correctly graduated. But you can spend a little money and buy a digital voltmeter (its price is about a hundred rubles), whose measurement range is in the range of 0 ... 30 volts. It will be much easier to work with it, because you will always see the voltage value at the output of your power supply.
Computer power supply
To put it bluntly, this is the perfect device. From it you can make any source of constant voltage. True, not everyone knows how to run it without motherboard. It is very simple to do this - look for one green in the wiring harness and connect it to any black. That's all, you can see how the fans spin. Now more about how to make a laboratory power supply from a computer PSU with your own hands.
Voltage in a computer power supply
The fact is that you can find several types of voltages in a computer power supply:
- 3.3 V.
- 12 V.
As you understand, these are the most "popular" voltage values. They are enough to power microcircuits, controllers, actuators. Please note that even a complex electronic mechanism can be powered from a computer power supply alone. If only there was a decent supply of power.
High frequency currents
Most importantly, you can make a laboratory power supply from a computer PSU with a high-frequency current at the output. For some devices, such as monitor backlight inverters, it is the RF current that is needed. As you know, a computer PSU is built according to an inverter circuit. Therefore, somewhere in it you can find a voltage of 12 volts with a high frequency. To do this, do the following:
- Disassemble the power supply housing (unplug it first).
- Find the largest transformer. This is a high-frequency transformer, it is on it that the high-frequency current will be located.
- Solder two wires to the primary winding and lead out of the case.
Now it remains only to arrange everything beautifully - to make the front panel, install the required number of sockets and sign them so as not to get confused. When making a laboratory power supply from a computer PSU, you get one big advantage - the output voltage is always stable. Additional stabilization circuits are not required. And the 0-30V laboratory power supply considered at the very beginning turns out to be much worse in terms of parameters than from a computer PSU.
Conclusion
You can argue about the advantages and disadvantages of various schemes, but the best quality product will be a power supply from a computer PSU. But it has a drawback - a short circuit at the output leads to the transition of the power supply into protection mode. In fact, this is a complete stoppage of work. Only a reboot of the device will return the output voltage. But if the laboratory power supply is made according to the classical transformer circuit, you can avoid such problems - but you will have to think about protection against short circuit(at least a 16 or 25 amp fuse at the output of the device).
