Today the cost of a laboratory power supply is approximately 10 thousand rubles. But it turns out that there is an option to convert a computer power supply into a laboratory one. For just a thousand rubles you get short circuit protection, cooling, overload protection and several voltage lines: 3V, 5V and 12V. However, we will be modifying it to provide a range of 1.5 to 24V, which is ideal for most electronics.
I believe that this method of converting a computer power supply to 24 volts is the best, considering that I was able to make it a reality with my own hands at only 14 years old.
WARNING: Electrical work is being done here, be careful and follow safety precautions!
You will need:
Not necessary:
Depending on which method you use for a regulated power supply from the computer's power supply (more on this later):
Warning: BEFORE YOU START, MAKE SURE THE POWER SUPPLY IS NOT CONNECTED
Capacitors can give you an electric shock, which is quite painful. Let the power supply sit for a few days to drain, or connect a 10 ohm resistor to the red and black wires.
If you hear a buzzing noise when you turn on the power, it means there is a short circuit or other serious problem going on somewhere. If you hear a buzzing sound (not from the soldering iron) while soldering, it means the power supply is connected. Remember that if a unit that is connected to power is turned off with a button, there will still be current in it.
Okay, let's remove the power supply from the computer. It is usually attached with 4 screws to the rear panel of the case. Remove the wires from the hole, then group them by color and cut off the ends.
By the way, you just voided your warranty.
Now let's get to the tricky part where you need to add LEDs, switches and other such parts. We have a lot of each type of wire, so I recommend using 2-4 wires. Some people do everything inside the box, but I did everything outside. It depends on which method you use in the next step.
If you want to add a standby indicator or a power-on indicator, you will need an LED (red is recommended, but not required) and a 330 ohm resistor. Solder the black wire to one end of the resistor and the short end of the LED to the other. The resistor will reduce the voltage so as not to damage the LED. Before soldering, apply a small piece of heat shrink to protect the contacts from short circuiting. Solder the purple wire to the longer leg and when you apply power (not turning on the unit) the LED should light up.
For the power supply that is on, you can also set a different LED (I recommend green). Some people say to use a gray wire to power the LED, but then you need another 330 ohm resistor. I just connected it to the orange 3.3V wire.
If you are using the gray wire method:
Before soldering it, put on another piece of heat shrink to prevent short circuit. Solder the gray wire to one end of the resistor and the other end of the resistor to the longer leg of the LED. Solder the black wire to the short leg.
When using the orange 3.3V wire:
Before soldering it, put on another piece of heat shrink to prevent short circuit. Solder the orange wire to the longer leg of the LED and the black wire to the shorter leg.
Now to the switch: if there is already a switch on the back of your power supply, this item will not be of much use to you. Connect the green wire to one terminal on the switch and the black wire to the other. If you don't want to use a switch, just connect the green and black wires.
You can also use a 1A fuse. All you have to do is cut the black wires approximately in the middle, and connect them to the fuse in the holder.
Some power supplies require a load to operate properly. To provide this load, solder the red wire to one end of the 10 Ohm\10 W resistor and the black wire to the other. This way the block will think it is doing something.
If you don't understand anything, take a look at the diagram I've attached. It shows how to connect the wires. I'll talk about this in the next step. It shows a method with a gray wire to the LED (but you can use orange as described above), and also shows the wiring for a high resistance resistor.
In the tutorials I've read, there are many different ways to connect the connectors to connect your devices to power. We'll start with the best and work our way down to the worst.
Some tutorials will tell you how to assemble all the parts inside the case, but this is dangerous and will cause excessive heat and damage. I recommend using external mounting.
I personally think this is the best method since it can provide any voltage from 1.5 to 24V. The reason it is 22V and not 12V is because it uses the blue wire which is -12V. and not regular ground (black wire).
We will need:
First build the circuit from the main image and connect your +12V and -12V lines. Then drill holes in the power supply or external case to install the variable resistor. All other parts must be inside. Now I suggest adding two terminal blocks so that you can connect devices directly. You can also connect “crocodiles” to them. When you turn the variable resistor, the voltage should be between 1.5 and 24 V.
NOTE. There is a typo in the main image that should be taken into account: +24V instead of 22V. If you have an old voltmeter, you can connect it to the circuit to monitor the voltage output.
Now you need to install the connectors to connect the equipment. Drill holes for them (be sure to wrap the PCB in plastic as metal shards can short it out) and then check they fit by inserting the connectors and tightening the bolt. Select what voltage should go to each connector and how many connectors you want to insert. Wire color codes:
Above is an image using the connector method.
If you don't have much experience or don't have the above parts and for some reason you can't buy them, you can just connect whatever voltage lines you want to the alligator clips. If you choose this option, I recommend using insulation to prevent short circuits.
Congratulations! You have successfully made your power supply.
Not only radio amateurs, but also just in everyday life, may need a powerful power supply. So that there is up to 10A output current at a maximum voltage of up to 20 volts or more. Of course, the thought immediately goes to unnecessary ATX computer power supplies. Before you start remaking, find a diagram for your specific power supply.
1. Remove jumper J13 (you can use wire cutters)
2. Remove diode D29 (you can just lift one leg)
3. The PS-ON jumper to ground is already installed.
5. Remove the 3.3-volt part: R32, Q5, R35, R34, IC2, C22, C21.
8. We change the bad ones: replace C11, C12 (preferably with a larger capacity C11 - 1000uF, C12 - 470uF).
9. We change the inappropriate components: C16 (preferably 3300uF x 35V like mine, well, at least 2200uF x 35V is a must!) and resistor R27 - you no longer have it, and that’s great. I advise you to replace it with a more powerful one, for example 2W and take the resistance to 360-560 Ohms. We look at my board and repeat:
12. We separate the 15th and 16th legs of the microcircuit from “all the rest”, to do this we make 3 cuts in the existing tracks and restore the connection to the 14th leg with a jumper, as shown in the photo.
14. The core of cable No. 7 (the regulator’s power supply) can be taken from the +17V power supply of the TL, in the area of the jumper, more precisely from it J10/ Drill a hole into the track, clear the varnish and there. It is better to drill from the print side.
Or how to make a cheap power supply for a 100 W amplifier
How much will a 300 Watt ULF cost?
Depends on what for :)
Listen at home!
Bucks *** will be normal...
OMG! Is there any way to get it cheaper?
Mmmmm... We need to think...
And I remembered about a pulse power supply, powerful and reliable enough for ULF.
And I started thinking about how to remake it to suit our needs :)
After some negotiations, the person for whom all this was planned lowered the power level from 300 watts to 100-150 and agreed to take pity on the neighbors. Accordingly, a 200 W pulse generator will be more than enough.
As you know, an ATX format computer power supply gives us 12, 5 and 3.3 V. AT power supplies also had a voltage of “-5 V”. We don't need these tensions.
In the first power supply unit that came across, which was opened for rework, there was a PWM chip, beloved by the people - TL494.
This power supply was an ATX 200 W brand, I don’t remember which one. Not particularly important. Since my friend was “on fire,” the ULF cascade was simply purchased. It was a mono amplifier based on the TDA7294, which can output 100 W peak, which was quite satisfactory. The amplifier required bipolar +-40V power supply.
We remove everything superfluous and unnecessary in the decoupled (cold) part of the power supply, leaving the pulse shaper and the OS circuit. We install Schottky diodes that are more powerful and at a higher voltage (in the converted power supply they were 100 V). We also install electrolytic capacitors whose voltage exceeds the required voltage by 10-20 volts for reserve. Fortunately, there is a place to roam.
Look at the photo with caution: not all elements are worthy :)
Now the main “reworked part” is the transformer. There are two options:
I didn't bother and chose the second option.
We disassemble it and solder the windings in series, not forgetting to make a middle point:
To do this, the transformer leads were disconnected, ringed and twisted in series.
In order to see whether I made a mistake in the winding in a serial connection or not, I fired pulses with a generator and looked at what came out at the output with an oscilloscope.
At the end of these manipulations, I connected all the windings and made sure that from the middle point they have the same voltage.
We put it in place, calculate the OS circuit on the TL494 at 2.5V from the output with a voltage divider to the second leg and connect it in series through a 100W lamp. If everything works well, we add one more and then another hundred-watt lamp to the garland chain. For insurance against accidental parts flying :)
Lamp as a fuse
The lamp should blink and go out. It is highly advisable to have an oscilloscope to be able to see what is happening on the microcircuit and the drive transistors.
By the way, for those who don’t know how to use datasheets, let’s learn. Datasheets and Google help better than forums if you have developed the “Google” and “translator with an alternative point of view” skills.
I found an approximate power supply diagram 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 it's a very rough approximation and there's a lot of detail missing!
The speaker design was coordinated and interfaced with the power supply and amplifier. It turned out simple and nice:
On the right - under the cut-off radiator for the video card and computer cooler there is an amplifier, on the left - its power supply. The power supply produced stabilized voltages of +-40 V on the positive voltage side. The load was something like 3.8 Ohms (there are two speakers in the column). It fits compactly and works like a charm!
The presentation of the material is rather incomplete; I missed many points, since this happened several years ago. To help with repetition, I can recommend circuits from powerful low-frequency car amplifiers - there are bipolar converters, usually 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... Feels reliable and will soon join the army :)
We remind you that you can also find us in the VKontakte group, where every question will definitely be answered!
Usually, ATX units assembled on TL494 (KA7500) chips are used to remake computer power supplies, but recently such units have not come across. They began to be assembled on more specialized microcircuits, on which it is more difficult to adjust the current and voltage from scratch. For this reason, an old 200W AT type unit that was available was taken for modification.
2. The self-starting parts of the primary circuit and the output voltage regulation circuit are soldered off the AT block board. All secondary rectifiers were also removed.
The shunt requires special attention; the wires for adjustment and measurement must be connected directly to its terminals, since the voltage removed from it is small. In the diagram these connections are shown with purple arrows. The measured voltage for the control circuit is removed from the divider with correction to eliminate self-excitation in the control circuits.
The upper limit of the voltage setting is selected by resistors R38, R39 and R40. The upper limit of the current setting is selected by resistor R13.
3. A voltmeter-ammeter is used to measure current and voltage
4. The program for the microcontroller is written in SI (mikroC PRO for PIC) and provided with comments.
The drawings were made in the Frontplatten-Designer 1.0 program. The interstage transformer of the AT block is not modified. The output transformer of the AT block is also not modified, just the middle tap coming out of the coil is unsoldered from the board and isolated. The rectifier diodes were replaced with new ones indicated in the diagram.
The shunt was taken from a faulty tester and mounted on insulating stands on a radiator with diodes. The board for the voltmeter-ammeter is used from “Super simple ammeter and voltmeter on super affordable parts (auto range selection)” from Eddy71 with subsequent modification (paths were cut according to the diagram).
They often ask questions and complain about failures. To show that alteration is indeed possible and it is not at all difficult, we have prepared another article, with illustrations and explanations.
Let us remind you that you can remake any blocks, both AT and ATX. The first ones are distinguished simply by the absence of a duty officer. As a result, the TL494 in them is powered directly from the output of the power transformer, and, again, as a consequence, when adjusting at low loads, it simply will not have enough power, because the duty cycle of the pulses on the primary of the transformer will be too small. The introduction of a separate power supply for the microcircuit solves the problem, but requires additional space in the case.
ATX power supplies have an advantage here in that you don’t need to add anything, you just need to remove the excess and add, roughly speaking, two variable resistors.
The ATX MAV-300W-P4 computer power supply is being reworked. The task is to convert it into a laboratory 0-24V, according to the current - as it turns out. They say that they manage to get 10A. Well, let's check.
Click on the diagram to enlarge
The power supply circuit is easy to google, but you can do without it, because we know that from the TL494 we will need the inputs of both comparators, and these are pins 1, 2, 15, 16, and their common output 3, which is usually used for correction. We also release pin 4, since it is usually used for various protections. However, we leave capacitor C22 and resistor R46 hanging on it for a smooth start. We unsolder only diode D17, disconnecting the voltage monitor from the TL.
Add resistors, regulators, shunt. As the latter, two 0.025 Ohm SMD resistors were used in parallel, which are included in the gap in the negative track from the transformer.
We connect the power supply to the network through a 200W incandescent lamp, which is designed to protect against breakdown of power transistors in the event of an emergency. At idle, the voltage is perfectly regulated from almost 0 to 24 volts. What will happen under load? We connect several powerful halogen lamps and see that the voltage is regulated to 20 volts. This is to be expected since we are using 12V windings and a midpoint rectifier. At a powerful load, PWM is already at its limit and it is no longer possible to get more.
What to do? You can simply use a power supply to power not very powerful loads. But what to do if you really want to get the coveted 10 amps, especially since on the power supply label they are stated for a 12 volt line? Everything is very simple: we change the rectifier to a classic bridge of four diodes, thereby increasing the voltage amplitude at its output. To do this, you will need to install two more diodes. The diagram shows that such diodes were just installed, these are D24 and D25, along the -12 volt line. Unfortunately, their location on the board is not good for our case, so we will have to use diodes in “transistor” packages and either install separate radiators on them, or attach them to a common radiator and solder them with wiring. The requirements for diodes are the same: fast, powerful, for the required voltage.
With a converted rectifier, the voltage, even with a powerful load, is regulated from 0 to 24 volts, and current regulation also works.
There is one more problem left to solve - fan power. It is impossible to leave the power supply without active cooling, because the power transistors and rectifier diodes heat up according to the load. Standardly, the fan was powered from a +12 volt line, which we turned into an adjustable one with a voltage range slightly wider than the fan needed. Therefore, the simplest solution is to power it from the duty room. To do this, we replace capacitor C13 with a more capacitive one, increasing its capacity by 10 times. The voltage at the cathode D10 is 16 volts, and we take it for the fan, only through a resistor, the resistance of which must be selected so that the fan is 12 volts. As a bonus, you can output a good five-volt +5VSB power line from this power supply.
The requirements for the inductor are the same: we wind all the windings from the DGS and wind a new one: from 20 turns, 10 wires with a diameter of 0.5 mm in parallel. Of course, such a thick core may not fit into the ring, so the number of parallel wires can be reduced according to your load. For a maximum current of 10 amperes, the inductance of the inductor should be around 20uH.
A shunt built into an ammeter can be used as a shunt, and vice versa - a shunt can be used to connect an ammeter without a built-in shunt. The shunt resistance is around 0.01 Ohm. By decreasing the resistance of resistor R, you can increase the range of voltage adjustment upward.
