Good laboratory unit food is a rather expensive pleasure 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 can also cope with providing power to various radio amateur designs, and can also serve as a charger for various batteries.
Radio amateurs collect such power supplies, as a rule from, which are available everywhere and are cheap.

In this article, little attention has been paid to the ATX alteration itself, since it is usually not difficult to convert a computer power supply unit for an average radio amateur into a laboratory one, or for some other purpose, but novice radio amateurs have many questions about this. Basically, which parts in the power supply unit need to be removed, which ones should be left, what to add in order to turn such a power supply unit into an adjustable one, and so on.

Here, especially for such radio amateurs, I want to talk in detail in this article 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 the alteration, 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 everything is basically similar. The power of the power supply unit should not be less than what you plan to remove from the converted unit in the future.

let's consider typical scheme ATX power supply unit, 250 watts. The "Codegen" power supplies have the same circuit as this one.

The circuits of all such power supply units consist of a high-voltage and a low-voltage part. On the image printed circuit board the power supply unit (below) from the side of the tracks, the high-voltage part is separated from the low-voltage by a wide empty strip (no tracks), and is located on the right (it is smaller in size). We will not touch it, but will only work with the low-voltage part.
This is my board and, using its example, I will show you an option for reworking the ATX power supply unit.

The low-voltage part of the circuit we are considering consists of a TL494 PWM controller, a circuit based on operational amplifiers that controls the output voltages of the power supply, and if they do not match, it gives a signal to the 4th leg of the PWM controller to turn off the power supply.
Instead of an operational amplifier, transistors can be installed on the power supply 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 will be needed for our purposes (yellow output wires).
The rest of the rectifiers and their accompanying parts will need to be removed, except for the "duty room" rectifier, which we need to power the PWM controller and cooler.
The duty room rectifier provides two voltages. Usually this is 5 volts and the second voltage can be in the region of 10-20 volts (usually around 12).
We will use a second rectifier to power the PWM. A fan (cooler) is also connected to it.
If this output voltage will be 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've marked the high voltage part with a green line, the duty room rectifiers with a blue line, and everything else that needs to be removed - 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 power supply unit. It will also be necessary to unsolder 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 a jumper into the board, which is drawn in the diagram with a blue line (you can simply close diode and resistor without soldering them). Some circuits may not have this circuit.

Further, in the PWM harness on its first leg, we leave only one resistor, which goes to the +12 volt rectifier.
On the second and third legs of the PWM, we leave only the Master RC circuit (R48 C28 in the diagram).
On the fourth leg of the PWM, we leave only one resistor (in the diagram it is designated as R49. Yes, in many circuits between the 4th leg and 13-14 PWM legs - there is usually an electrolytic capacitor, we also do not touch it (if any), since it is intended for a soft start of the power supply unit.It simply was not in my board, so I installed it.
Its capacity in standard circuits is 1-10 microfarad.
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.

This is how it looks on my board (below in the figure).
Here I rewound the group stabilization choke with a 1.3-1.6 mm wire in one layer on my own core. Placed somewhere about 20 turns, but you can not do this and leave the one that was. Everything works well with him too.
I also installed another load resistor on the board, which I have consists of two resistors connected in parallel, 1.2 kOhm 3W each, the total resistance turned out to be 560 Ohm.
The native pull-up 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 is not at all desirable without load, therefore it is put into the circuit.

View of the board from the side of the parts.

Now, what will we need to add to the prepared board of our PSU in order to turn it into a regulated 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 I gave such a quote, I will give it in full:

"I once said that I could not get the UPS to work normally in the 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 - no matter how it worked. It does not work steadily and gets excited or gets lost from interference. This is when the signal voltage from the current sensor is positive.
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.
First, the best stability when stabilizing the load current with a negative signal from the current sensor is it a coincidence or a regularity?
The circuit works great 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 25 mV).
With resistor values ​​of 10 Ohm and 10KOhm, the current stabilized at the level of 1.5A up to the short-circuit output.
I need more current, so I put a resistor at 30 Ohm. The stabilization was at the level of 12 ... 13A with a reference voltage of 15mV.
Secondly (and most interesting), I don't have a current sensor as such ...
Its role is played by a fragment of the track 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 will stabilize at the level of 12-13A, and if at a length of 2.5 cm, then at the level of 10A. "

Since this result turned out to be better than the standard one, then we will go the same way.

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 seal 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 terminal of the winding with the negative wire.

It is best to take shunts from faulty (if you find) dial ammeter voltmeters (tseshek), or from Chinese dial or digital devices. They look something like this. A piece 1.5-2.0 cm long will be quite enough.

You can, of course, try to do the same as I wrote 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 did not do this, I got a board of a different design, this one where two wire jumpers are indicated by a red arrow that connected the output braids with a common wire, and printed paths passed between them.

Therefore, after removing unnecessary parts from the board, I dropped these jumpers and in their place I soldered a current sensor from a faulty Chinese "chain".
Then I soldered the rewound choke in place, installed the electrolyte and the load resistor.
Here's how a piece of the board looks like, where I marked the installed current sensor (shunt) in place of the wire jumper with a red arrow.

Then it is necessary to connect this shunt with a separate wire 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 the common wire.
Using a 10 Ohm resistor, it will be possible to select the maximum output current of our power supply unit. In 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 before, the output voltage of the power supply is about 40 volts. To do this, I rewound myself a 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 will talk about all this a little later, but for now we will continue and start installing the necessary additional parts on the board so that we have 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 keep the connection wires as short as possible.
Below I have given only part of the circuit that we need - it will be easier to understand such a circuit.
In the diagram, newly installed parts are indicated in green.

Diagram of newly installed parts.

I will give a little explanation of the scheme;
- The topmost rectifier is the duty room.
- The values ​​of variable resistors are shown as 3.3 and 10 kOhm - they are as they were found.
- The value of the resistor R1 is indicated as 270 Ohm - it is selected according to the required current limitation. Start small and you may have a completely different value, for example, 27 ohms;
- I did not mark the 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 during the BP setup process.

Next, we deal with the remaining 12-volt rectifier.
We check what maximum voltage our power supply unit 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 scheme above by 24 kOhm), then you need to turn on the unit to 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 mains, make sure that electrolytic capacitors in the output rectifier are replaced with higher voltage ones!

All further switching on of the power supply unit should be performed only with an incandescent lamp, it will save the power supply unit from emergencies, in the event 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 kOhm resistor (according to the scheme above) from the first leg of the PWM, we temporarily change it to a trimmer, for example, 100 kOhm, and set them to the maximum voltage we need. It is advisable to set it so that it would be less than 10-15 percent of the maximum voltage that our power supply unit is capable of delivering. Then solder a constant in place of the trimmer resistor.

If you plan to use this PSU as charger, then the regular diode assembly used in this rectifier, you can leave, since its reverse voltage is 40 volts and it is quite suitable for a charger.
Then the maximum output voltage of the future charger will need to be limited in the above described way, in the region of 15-16 volts. For a 12-volt battery charger, this is quite enough and there is no need to increase this threshold.
If you plan to use your converted PSU as regulated unit power supply, where the output voltage will be more than 20 volts, then this assembly will no longer work. It will need to be replaced with a higher voltage one with an appropriate load current.
On my own board, I put two assemblies in parallel, 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 power supply unit for the maximum output voltage, the power supply unit outputs a voltage less than the planned one, and someone will need more output voltage (40-50 volts, for example), then instead of the diode assembly it will be necessary to assemble a diode bridge, unsolder the braid from its place and leave it hanging in the air, and connect the negative terminal of the diode bridge to the place of the soldered braid.

Rectifier circuit with diode bridge.

With a diode bridge, the output voltage of the power supply will be twice that.
KD213 diodes (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). Best of all, of course, the latter.
They all look like this;

In this case, it will be necessary to think over the fastening of the diodes to the radiator and their isolation 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 there was a place for this on the board. This path turned out to be easier for me.

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

First, we solder the transformer from the board and look at the board to which terminals 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 a 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 (maybe less) and such a procedure will absolutely not damage the core and the 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, since 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 up the windings. First comes half of the primary winding, mostly about 20 turns. We wind it up and remember the winding direction. The second end of this winding may not be unsoldered 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 up all the secondary housing. Usually there are 4 turns of both halves of the 12-volt windings at once, then 3 + 3 turns of 5-volt windings. We wind everything up, unsolder it from the terminals and wind up 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 corresponding section.
We solder the beginning of the winding to one of the terminals, to which a 12-volt winding was soldered, we wind 10 turns, the winding direction does not matter, we withdraw the tap to the "braid" and in the same direction as we started - we wind another 10 turns and end solder to the remaining output.
Then we isolate the secondary and wind the second half of the primary onto it, which we wound earlier, in the same direction as it was wound earlier.
We assemble the transformer, solder it into the board and check the operation of the power supply unit.

If in the process of voltage regulation any extraneous noises, squeaks, cods appear, 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. You can try adding a capacitor, or the same RC circuit, between the 3 and 15 PWM pins.
If this does not help, then you need to install additional capacitors (circled in orange), their values ​​are approximately 0.01 μF. If this does not help much, then install an additional 4.7 kΩ resistor from the second leg of the PWM to the middle terminal of the voltage regulator (not shown in the diagram).

Then you will need to load the PSU 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 Ohm), and again try to adjust the current.
You should not put a trimmer instead of this resistor, 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 network wire circuit will light up. Then you need to reduce the current, turn off the power supply 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. It is regulated at first "Smoothly", then when it reaches the limit, it starts to be regulated "Coarsely".
Adjustment with such resistors is very convenient, fast and accurate, much better than a multi-turn. But if you can't get them, then get the usual multi-turn ones, for example;

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

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

Good luck with your design!

Many people assemble various electronic structures and sometimes require a powerful power source to use them. Today I will 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 an ATX model FA-5-2.

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

Alteration of the ATX unit will consist of several stages

1. First, we solder the wires, leaving only gray, black, yellow. By the way, to turn on this unit, you need to short the green wire to ground (as in most ATX units), but the gray wire.

2. We solder the parts from the circuit that are in the + 3.3v, -5v, -12v circuits (do not 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 trimmer 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 short the gray wire to ground, having previously put the trimmer resistor in the middle position, and the variable resistor in 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, as we do not have voltage protection yet.

4. We make protection in terms of power and voltage. Add two trimming resistors:

5. Indicator 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 integrate a voltammeter.

Setting the voltage protection in the power supply

Setting the voltage protection 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 rotate R2 to achieve the voltage we need - 16 volts, but set 0.2 volts more - 16.2 volts, slowly turn R4 before the protection is triggered, 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 during the last operation the protection worked, then you overrun with the R4 turn and you will have to repeat everything again. After configuring the protection, the laboratory unit is completely ready for use.

Over the past month, I have already made three such units, each cost me about 500 rubles (this is together with a voltammeter, which I collected separately for 150 rubles). And I sold one power supply unit, as a charger for a machine battery, for 2,100 rubles, so it's already in the black :)

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

How to make a full-fledged power supply with a range yourself regulated voltage 2.5-24 volts, very simple, can be repeated by everyone without having any amateur radio experience behind them.

We will make from the old computer unit power supply, TX or ATX without a difference, fortunately, over the years of the PC Era, every house has already accumulated a sufficient amount of old computer hardware and the power supply unit is probably also there, so the cost price homemade will be insignificant, and for some masters it is equal to zero rubles.

I got this AT block for alteration.

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

See what is written on the case.

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

There are many options for finalizing a standard computer power supply unit, but they are all based on a change in the binding of the IC chip - TL494CN (its counterparts DBL494, КА7500, IR3M02, A494, MV3759, M1114EU, МPC494C, etc.).

Fig. No. 0 Pinout of the TL494CN microcircuit and analogs.

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

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 search for an option on the Internet for your IC.

In my case, a KA7500 microcircuit was found on the board, which means we can start studying the strapping and the location of the parts we don't need that need to be removed.

For the convenience of work, first completely unscrew the entire board and remove it from the case.

In the photo, the power connector is 220v.

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

There is no green wire in my AT block, so it starts up immediately when plugged into the outlet. If the ATX unit, then it must have a green wire, it must be soldered to the "common" one, and if you want to make a separate power button on the case, then just put the switch in the break 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 for blue.

This is done because our modified unit will not give out +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 selecting 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 harness IC494, and solder other denominations of the parts, so that the result is such a harness (Fig. №1).

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

We will only need these legs of the microcircuit # 1, 2, 3, 4, 15 and 16, do not pay attention to the rest.

Rice. No. 2 Option revision on the example of scheme No. 1

Decoding of designations.

You need to do something like this, we find leg # 1 (where there is a point on the case) of the microcircuit and study what is connected to it, all circuits must be removed, disconnected. Depending on how the tracks will be located in your particular board modification and the parts are soldered, the optimal revision option is selected, it can be soldering and raising one leg of the part (breaking the chain) or it will be easier to cut the track with a knife. Having decided on an action plan, we begin the rework process according to the revision scheme.

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

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

Some resistors that are already soldered into the strapping circuit can come up without replacing them, for example, we need to put a resistor at R = 2.7k connected to the "common", but there is already R = 3k connected to the "common", this suits us perfectly and we leave it there unchanged (example in Fig. №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 point in the alteration.

We make voltage and current regulators.

We take variable resistors at 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. №1). Install on the front panel.

Voltage and current monitoring.
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 delivery. (Voltmeter :)

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

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

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