How to make a full-fledged power supply yourself with an adjustable voltage range of 2.5-24 volts, but it’s very simple, everyone can repeat without amateur radio experience behind them.

We will make it from an old computer power supply, TX or ATX, it doesn’t matter, fortunately, over the years of the PC Era, each house has already accumulated enough old computer hardware and the PSU is probably also there, so the cost of homemade products will be insignificant, and for some masters it is equal to zero rubles .

I got to remake this is the AT block.

The more powerful you use the PSU, the better the result, my donor is only 250W with 10 amps on the + 12v bus, but in fact, with a load of only 4 A, it can no longer cope, there is a complete drawdown of the output voltage.

See what is written on the case.

Therefore, see for yourself what current you plan to receive from your regulated PSU, such a donor potential and lay it right away.

There are many options for improving a standard computer PSU, but all of them are based on a change in the binding of the IC chip - TL494CN (its analogues are DBL494, KA7500, IR3M02, A494, MB3759, M1114EU, MPC494C, etc.).

Fig No. 0 Pinout of the TL494CN chip and analogues.

Let's see some options execution of computer power supply circuits, perhaps one of them will turn out to be yours and it will become much easier to deal with the strapping.

Scheme No. 1.

Let's get to work.
First you need to disassemble the PSU case, unscrew the four bolts, remove the cover and look inside.

We are looking for a microcircuit from the list above on the board, if there is none, then you can look for a refinement option on the Internet for your IC.

In my case, the KA7500 chip was found on the board, which means that we can begin to study the strapping and the location of the parts we do not need that need to be removed.

For ease of use, first completely unscrew the entire board and remove it from the case.

In the photo, the power connector is 220v.

Disconnect the power and the fan, solder or bite out the output wires so as not to interfere with our understanding of the circuit, leave only the necessary ones, one yellow (+ 12v), black (common) and green * (ON start) if there is one.

My AT unit does not have a green wire, so it starts up immediately when plugged into a power outlet. If the ATX unit, then it should have a green wire, it must be soldered to the "common", and if you want to make a separate power button on the case, then simply put the switch in the gap of this wire.

Now you need to look at how many volts the output large capacitors cost, if less than 30v is written on them, then you need to replace them with similar ones, only with an operating voltage of at least 30 volts.

In the photo - black capacitors as a replacement option for blue.

This is done because our modified unit will not produce +12 volts, but up to +24 volts, and without replacement, the capacitors will simply explode during the first test at 24v, after a few minutes of operation. When choosing a new electrolyte, it is not advisable to reduce the capacity, it is always recommended to increase it.

The most important part of the job.
We will remove all unnecessary in the IC494 harness, and solder other parts denominations, so that the result is such a harness (Fig. No. 1).

Rice. No. 1 Change in the binding of the IC 494 microcircuit (revision scheme).

We will need only these legs of the microcircuit No. 1, 2, 3, 4, 15 and 16, do not pay attention to the rest.

Rice. No. 2 Refinement option using the example of scheme No. 1

Decoding of designations.

Should be done like this, we find leg No. 1 (where there is a dot on the case) of the microcircuit and study what is attached to it, all circuits must be removed, disconnected. Depending on how you have tracks in a particular modification of the board and soldered parts, the best option for refinement is selected, it can be soldering and lifting one leg of the part (breaking the chain) or it will be easier to cut the track with a knife. Having decided on the action plan, we begin the process of rework according to the refinement scheme.

In the photo - replacing the resistors with the desired value.

In the photo - by raising the legs of unnecessary parts, we break the chains.

Some resistors that are already soldered into the piping circuit may be suitable without replacing them, for example, we need to put a resistor at R=2.7k connected to "common", but there is already R=3k connected to "common", this suits us perfectly and we leave it there unchanged (example in Fig. No. 2, green resistors do not change).

On the picture- cut tracks and added new jumpers, write down the old denominations with a marker, you may need to restore everything back.

Thus, we view and redo all the circuits on the six legs of the microcircuit.

This was the most difficult item in the alteration.

We make voltage and current regulators.

We take variable resistors of 22k (voltage regulator) and 330Ω (current regulator), solder two 15cm wires to them, solder the other ends to the board according to the diagram (Fig. No. 1). Installed on the front panel.

Voltage and current control.
For control, we need a voltmeter (0-30v) and an ammeter (0-6A).

These devices can be purchased in Chinese online stores at the best price, my voltmeter cost me only 60 rubles with delivery. (Voltmeter: )

I used my ammeter, from the old stocks of the USSR.

IMPORTANT- inside the device there is a Current resistor (Current sensor), which we need according to the scheme (Fig. No. 1), therefore, if you use an ammeter, you do not need to install an additional Current resistor, you need to install it without an ammeter. Usually R Current is made home-made, a wire D = 0.5-0.6 mm is wound on a 2-watt MLT resistance, turn to turn for the entire length, solder the ends to the resistance leads, that's all.

Everyone will make the body of the device for themselves.
You can leave completely metal by cutting holes for regulators and control devices. I used laminate cutoffs, they are easier to drill and cut.

Many people assemble various electronic structures and sometimes a powerful power source is required to use them. Today I'll tell you how with an output power of 250 watts, and the ability to adjust the voltage from 8 to 16 volts at the output, from the ATX block model FA-5-2.

The advantage of this PSU is output power protection (that is, short circuit protection) and voltage protection.

Alteration of the ATX block will consist of several stages

1. To begin with, we solder the wires, leaving only gray, black, yellow. By the way, to turn on this unit, you need to short to ground not the green one (as in most ATX units), but the gray wire.

2. We solder the parts from the circuit that are in the circuits + 3.3v, -5v, -12v (we don’t touch +5 volts yet). What to remove is shown in red, and what to redo is shown in blue in the diagram:

3. Next, we solder (remove) the +5 volt circuit, replace the diode assembly in the 12v circuit with S30D40C (taken from the 5v circuit).

We put a tuning resistor and a variable resistor with a built-in switch as shown in the diagram:

That is like this:

Now we turn on the 220V network and close the gray wire to ground, after setting the trimmer resistor to the middle position, and the variable to the position at which it will have the least resistance. The output voltage should be about 8 volts, increasing the resistance of the variable resistor, the voltage will increase. But do not rush to raise the voltage, since we do not yet have voltage protection.

4. We make power and voltage protection. Add two trimmer resistors:

5. Display panel. Add a couple of transistors, some resistors and three LEDs:

The green LED lights up when connected to the network, yellow - when there is voltage at the output terminals, red - when the protection is triggered.

You can also build in a voltammeter.

Setting voltage protection in the power supply

The voltage protection setting is performed as follows: we twist the resistor R4 to the side where the mass is connected, set R3 to the maximum (greater resistance), then by rotating R2 we achieve the voltage we need - 16 volts, but set 0.2 volts more - 16.2 volts, slowly turn R4 before the protection trips, turn off the unit, slightly reduce the resistance R2, turn on the unit and increase the resistance R2 until the output is 16 volts. If the protection worked during the last operation, then you overdid the R4 turn and you have to repeat everything again. After setting up the protection, the laboratory unit is completely ready for use.

Over the past month, I have already made three such blocks, each cost me about 500 rubles (this is together with a voltammeter, which I collected separately for 150 rubles). And I sold one PSU as a charger for a car battery for 2100 rubles, so it’s already in the black :)

Ponomarev Artyom (stalker68) was with you, see you on the pages of Technoobzor!

A good laboratory power supply is quite expensive and not all radio amateurs can afford it.
Nevertheless, at home, you can assemble a power supply that is not bad in terms of characteristics, which will cope well with providing power to various amateur radio designs, and can also serve as a charger for various batteries.
Radio amateurs assemble such power supplies, usually from, which are available everywhere and cheap.

In this article, little attention is paid to the conversion of the ATX itself, since it is usually not difficult to convert a computer PSU for a medium-skilled radio amateur into a laboratory one, or for some other purpose, but beginner radio amateurs have a lot of questions about this. Basically, what parts in the PSU need to be removed, which ones to leave, what to add in order to turn such a PSU into an adjustable one, and so on.

Here, especially for such radio amateurs, in this article I want to talk in detail about the conversion of ATX computer power supplies into regulated power supplies, which can be used both as a laboratory power supply and as a charger.

For rework, we need a working ATX power supply, which is made on the TL494 PWM controller or its analogues.
The power supply circuits on such controllers, in principle, do not differ much from each other and are all mostly similar. The power of the power supply should not be less than that which you plan to remove from the converted unit in the future.

Let's look at a typical ATX power supply circuit with a power of 250 watts. For "Codegen" power supplies, the circuit is almost the same as this one.

The circuits of all such PSUs consist of a high-voltage and low-voltage part. In the figure of the power supply circuit board (below), from the side of the tracks, the high-voltage part is separated from the low-voltage by a wide empty strip (without tracks), and is located on the right (it is smaller in size). We will not touch it, but we will work only with the low-voltage part.
This is my board, and using its example, I will show you an option for reworking the ATX PSU.

The low-voltage part of the circuit we are considering consists of a TL494 PWM controller, an operational amplifier circuit that controls the output voltages of the power supply, and if they do not match, it gives a signal to the 4th pin of the PWM controller to turn off the power supply.
Instead of an operational amplifier, transistors can be installed on the PSU board, which, in principle, perform the same function.
Next comes the rectifier part, which consists of various output voltages, 12 volts, +5 volts, -5 volts, +3.3 volts, of which only a +12 volt rectifier (yellow output wires) will be needed for our purposes.
The rest of the rectifiers and their related parts will need to be removed, except for the "duty" rectifier, which we will need to power the PWM controller and cooler.
The duty rectifier provides two voltages. Usually this is 5 volts and the second voltage can be in the region of 10-20 volts (usually about 12).
We will use a second rectifier to power the PWM. A fan (cooler) is also connected to it.
If this output voltage is significantly higher than 12 volts, then the fan will need to be connected to this source through an additional resistor, as will be further in the considered circuits.
In the diagram below, I marked the high-voltage part with a green line, the "duty" rectifiers with a blue line, and everything else that needs to be removed is in red.

So, everything that is marked in red is soldered, and in our 12 volt rectifier we change the standard electrolytes (16 volts) to higher voltage ones that will correspond to the future output voltage of our PSU. It will also be necessary to solder in the circuit of the 12th leg of the PWM controller and the middle part of the winding of the matching transformer - resistor R25 and diode D73 (if they are in the circuit), and instead of them, solder the jumper into the board, which is drawn in the diagram with a blue line (you can simply close diode and resistor without soldering them). In some schemes, this circuit may not be.

Further, in the PWM harness on its first leg, we leave only one resistor that goes to the +12 volt rectifier.
On the second and third legs of the PWM, we leave only the Master RC chain (in the diagram R48 C28).
On the fourth leg of the PWM, we leave only one resistor (indicated as R49 on the diagram. Yes, in many circuits between the 4th leg and 13-14 legs of the PWM - there is usually an electrolytic capacitor, we don’t touch it (if any), since it is designed for a soft start of the power supply, it simply was not in my board, so I put it in.
Its capacitance in standard circuits is 1-10 microfarads.
Then we release the 13-14 legs from all connections, except for the connection with the capacitor, and also release the 15th and 16th PWM legs.

After all the operations performed, we should get the following.

Here's what it looks like on my board (below in the figure).
I rewound the group stabilization inductor here with a 1.3-1.6 mm wire in one layer on my native core. It fit somewhere around 20 turns, but you can not do this and leave the one that was. It also works well with him.
I also installed another load resistor on the board, which I have consists of two 1.2 kOhm 3W resistors connected in parallel, the total resistance turned out to be 560 Ohm.
The native load resistor is rated for 12 volts of output voltage and has a resistance of 270 ohms. My output voltage will be about 40 volts, so I put such a resistor.
It must be calculated (at the maximum output voltage of the PSU at idle) for a load current of 50-60 mA. Since the operation of the power supply unit without any load is not desirable, therefore it is put into the circuit.

View of the board from the side of the details.

Now what will we need to add to the prepared board of our PSU in order to turn it into an adjustable power supply;

First of all, in order not to burn the power transistors, we will need to solve the problem of stabilizing the load current and protecting against short circuits.
On the forums for the alteration of such blocks, I met such an interesting thing - when experimenting with the current stabilization mode, on the forum pro-radio, forum member DWD Here is a quote, here it is in full:

"I once said that I could not get the UPS to work normally in current source mode with a low reference voltage at one of the inputs of the PWM controller error amplifier.
More than 50mV is normal, less is not. In principle, 50mV is a guaranteed result, but in principle, you can get 25mV if you try. Less than that didn't work. It does not work steadily and is excited or confused by interference. This is with a positive voltage signal from the current sensor.
But in the datasheet on the TL494 there is an option when a negative voltage is removed from the current sensor.
I redid the circuit for this option and got an excellent result.
Here is a snippet of the diagram.

Actually, everything is standard, except for two points.
Firstly, is the best stability when stabilizing the load current with a negative signal from the current sensor, is it an accident or a pattern?
The circuit works fine with a reference voltage of 5mV!
With a positive signal from the current sensor, stable operation is obtained only at higher reference voltages (at least 25mV).
With resistor values ​​of 10Ω and 10KΩ, the current stabilized at 1.5A up to a short circuit of the output.
I need more current, so I put a 30 ohm resistor. Stabilization turned out at the level of 12 ... 13A at a reference voltage of 15mV.
Secondly (and most interesting), I don’t have a current sensor, as such ...
Its role is played by a track fragment on the board 3 cm long and 1 cm wide. The track is covered with a thin layer of solder.
If this track is used as a sensor at a length of 2 cm, then the current stabilizes at a level of 12-13A, and if at a length of 2.5 cm, then at a level of 10A.

Since this result turned out to be better than the standard one, we will follow the same path.

To begin with, you will need to unsolder the middle terminal of the secondary winding of the transformer (flexible braid) from the negative wire, or better without soldering it (if the signet allows) - cut the printed track on the board that connects it to the negative wire.
Next, you will need to solder a current sensor (shunt) between the cut of the track, which will connect the middle output of the winding to the negative wire.

Shunts are best taken from faulty (if you can find) pointer ammeters (tseshek), or from Chinese pointer or digital devices. They look like this. A piece 1.5-2.0 cm long will be quite enough.

You can of course try to do the same as above. DWD, that is, if the path from the braid to the common wire is long enough, then try to use it as a current sensor, but I didn’t do it, I got a board of a different design, like this, where two wire jumpers that connected the output are indicated by a red arrow braids with a common wire, and printed tracks passed between them.

Therefore, after removing unnecessary parts from the board, I unsoldered these jumpers and soldered a current sensor from a faulty Chinese circuit in their place.
Then I soldered the rewound inductor in place, installed the electrolyte and the load resistor.
Here is a piece of the board I have, where I marked the installed current sensor (shunt) with a red arrow at the place of the wire jumper.

Then, with a separate wire, this shunt must be connected to the PWM. From the side of the braid - with the 15th PWM leg through a 10 Ohm resistor, and connect the 16th PWM leg to a common wire.
Using a 10 ohm resistor, it will be possible to select the maximum output current of our PSU. On the diagram DWD there is a 30 ohm resistor, but start with 10 ohms for now. Increasing the value of this resistor increases the maximum output current of the PSU.

As I said earlier, the output voltage of the power supply is about 40 volts. To do this, I rewound my transformer, but in principle you can not rewind, but increase the output voltage in another way, but for me this method turned out to be more convenient.
I’ll talk about all this a little later, but for now, let’s continue and start installing the necessary additional parts on the board so that we get a workable power supply or charger.

Let me remind you once again that if you did not have a capacitor on the board between the 4th and 13-14 PWM legs (as in my case), then it is advisable to add it to the circuit.
You will also need to install two variable resistors (3.3-47 kOhm) to adjust the output voltage (V) and current (I) and connect them to the circuit below. It is desirable to make connection wires as short as possible.
Below I have given only a part of the circuit that we need - it will be easier to understand such a circuit.
In the diagram, newly installed parts are marked in green.

Scheme of newly installed parts.

I will give a few explanations according to the scheme;
- The uppermost rectifier is the duty room.
- The values ​​​​of variable resistors are shown as 3.3 and 10 kOhm - they are the ones that were found.
- The value of the resistor R1 is 270 ohms - it is selected according to the required current limit. Start small and you may end up with a completely different value, for example 27 ohms;
- I did not mark capacitor C3 as newly installed parts in the expectation that it may be present on the board;
- The orange line indicates the elements that may have to be selected or added to the circuit in the process of setting up the PSU.

Next, we deal with the remaining 12-volt rectifier.
We check what maximum voltage our PSU is capable of delivering.
To do this, temporarily unsolder from the first leg of the PWM - a resistor that goes to the output of the rectifier (according to the diagram above by 24 kOhm), then you need to turn on the unit in the network, first connect any network wire to the break, as a fuse - an ordinary incandescent lamp 75-95 Tue The power supply in this case will give us the maximum voltage that it is capable of.

Before connecting the power supply to the network, make sure that the electrolytic capacitors in the output rectifier are replaced with higher voltage ones!

All further switching on of the power supply unit should be carried out only with an incandescent lamp, it will save the power supply unit from emergency situations, in case of any mistakes made. The lamp in this case will simply light up, and the power transistors will remain intact.

Next, we need to fix (limit) the maximum output voltage of our PSU.
To do this, a 24 kΩ resistor (according to the diagram above) from the first PWM leg, we temporarily change it to a trimmer, for example 100 kΩ, and set the maximum voltage we need for them. It is advisable to set it so that it is less than 10-15 percent of the maximum voltage that our PSU is capable of delivering. Then, in place of the tuning resistor, solder a constant.

If you plan to use this PSU as a charger, then you can leave the standard diode assembly used in this rectifier, since its reverse voltage is 40 volts and it is quite suitable for the charger.
Then the maximum output voltage of the future charger will need to be limited in the manner described above, in the region of 15-16 volts. For a 12-volt battery charger, this is quite enough and it is not necessary to increase this threshold.
If you plan to use your converted PSU as a regulated power supply, where the output voltage will be more than 20 volts, then this assembly is no longer suitable. It will need to be replaced with a higher voltage one with the appropriate load current.
I put two assemblies in parallel on my board at 16 amperes and 200 volts.
When designing a rectifier on such assemblies, the maximum output voltage of the future power supply can be from 16 to 30-32 volts. It all depends on the model of the power supply.
If, when checking the PSU for the maximum output voltage, the PSU produces a voltage less than planned, and someone will need more output voltage (40-50 volts for example), then instead of a diode assembly, you will need to assemble a diode bridge, unsolder the braid from its place and leave it hanging in the air, and connect the negative output of the diode bridge to the place of the soldered braid.

Scheme of a rectifier with a diode bridge.

With a diode bridge, the output voltage of the power supply will be twice as much.
Diodes KD213 (with any letter) are very good for a diode bridge, the output current with which can reach up to 10 amperes, KD2999A, B (up to 20 amperes) and KD2997A, B (up to 30 amperes). The last ones are the best.
They all look like this;

In this case, it will be necessary to consider mounting the diodes to the radiator and isolating them from each other.
But I went the other way - I just rewound the transformer and managed, as I said above. two diode assemblies in parallel, since space was provided for this on the board. For me, this path was easier.

It is not difficult to rewind the transformer and how to do it - we will consider below.

To begin with, we unsolder the transformer from the board and look at the board to which pins the 12-volt windings are soldered.

Basically there are two types. Such as in the photo.
Next, you will need to disassemble the transformer. Of course, it will be easier to cope with smaller ones, but larger ones also lend themselves.
To do this, you need to clean the core from visible residues of varnish (glue), take a small container, pour water into it, put the transformer there, put it on the stove, bring to a boil and "cook" our transformer for 20-30 minutes.

For smaller transformers, this is quite enough (less can be) and such a procedure will absolutely not damage the core and windings of the transformer.
Then, holding the transformer core with tweezers (you can directly in the container) - with a sharp knife we ​​try to disconnect the ferrite jumper from the W-shaped core.

This is done quite easily, as the varnish softens from such a procedure.
Then just as carefully, we try to free the frame from the W-shaped core. This is also pretty easy to do.

Then we wind the windings. First comes half of the primary winding, mostly about 20 turns. We wind it and remember the direction of winding. The second end of this winding may not be soldered from the place of its connection with the other half of the primary, if this does not interfere with further work with the transformer.

Then we wind all the secondary ones. Usually there are 4 turns at once of both halves of 12-volt windings, then 3 + 3 turns of 5-volt ones. We wind everything, solder it from the conclusions and wind a new winding.
The new winding will contain 10+10 turns. We wind it with a wire with a diameter of 1.2 - 1.5 mm, or with a set of thinner wires (easier to wind) of the appropriate section.
The beginning of the winding is soldered to one of the terminals to which the 12-volt winding was soldered, we wind 10 turns, the winding direction does not matter, we bring the tap to the "braid" and in the same direction as we started - we wind another 10 turns and the end solder to the remaining output.
Next, we isolate the secondary and wind on it, wound by us earlier, the second half of the primary, in the same direction as it was wound earlier.
We assemble the transformer, solder it into the board and check the operation of the PSU.

If any extraneous noise, squeaks, cods occur during the voltage adjustment process, then in order to get rid of them, you will need to pick up an RC chain circled in an orange ellipse below in the figure.

In some cases, you can completely remove the resistor and pick up a capacitor, and in some it is impossible without a resistor. It will be possible to try adding a capacitor, or the same RC circuit, between 3 and 15 PWM legs.
If this does not help, then you need to install additional capacitors (circled in orange), their ratings are approximately 0.01 microfarads. If this does not help much, then install an additional 4.7 kΩ resistor from the second leg of the PWM to the middle output of the voltage regulator (not shown in the diagram).

Then you will need to load the power supply output, for example, with a 60 watt car lamp, and try to regulate the current with the "I" resistor.
If the current adjustment limit is small, then you need to increase the value of the resistor that comes from the shunt (10 ohms) and try to adjust the current again.
You should not put a tuning resistor instead of this, change its value only by installing another resistor with a higher or lower rating.

It may happen that when the current increases, the incandescent lamp in the mains wire circuit lights up. Then you need to reduce the current, turn off the PSU and return the resistor value to the previous value.

Also, for voltage and current regulators, it is best to try to purchase SP5-35 regulators, which come with wire and hard leads.

This is an analogue of multi-turn resistors (only one and a half turns), the axis of which is combined with a smooth and coarse regulator. First "Smooth" is adjusted, then when it runs out of limit, "Rough" starts to be regulated.
Adjustment with such resistors is very convenient, fast and accurate, much better than with a multi-turn. But if you can’t get them, then get the usual multi-turn ones, for example;

Well, it seems that I told you everything that I planned to bring to the alteration of the computer power supply, and I hope that everything is clear and intelligible.

If someone has any questions about the design of the power supply, ask them on the forum.

Good luck with your design!