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.
Sequence of actions for converting an ATX power supply into a regulated laboratory one.
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.
4. Turn on the PB only for a short time, since the input voltage will be maximum (approximately 20-24V). This is actually what we want to see. Don't forget about the output electrolytes, designed for 16V. They might get a little warm. Considering your “bloatiness”, they will still have to be sent to the swamp, it’s not a pity. I repeat: remove all the wires, they are in the way, and only ground wires will be used and +12V will then be soldered back.
5. Remove the 3.3-volt part: R32, Q5, R35, R34, IC2, C22, C21.
6. Removing 5V: Schottky assembly HS2, C17, C18, R28, or “choke type” L5.
7. Remove -12V -5V: D13-D16, D17, C20, R30, C19, R29.
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:
10. We remove everything from the legs TL494 1,2,3 for this we remove the resistors: R49-51 (free the 1st leg), R52-54 (...2nd leg), C26, J11 (...3- my leg)
11. I don’t know why, but my R38 was cut by someone :) I recommend that you cut it too. It participates in voltage feedback and is parallel to R37.
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.
13. Now we solder the cable from the regulator board to the points according to the diagram, I used the holes from the soldered resistors, but by the 14th and 15th I had to peel off the varnish and drill holes, 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.
I would also advise changing the high-voltage capacitors at the input (C1, C2). You have them in a very small container and are probably already pretty dry. There it will be normal to be 680uF x 200V. Now, let's assemble a small scarf on which there will be adjustment elements. See supporting files
Analysis of information on the modification of computer switching power supplies (hereinafter referred to as UPS), posted on the Internet, gave rise to the idea of converting the UPS for amateur radio purposes. Due to the wide variety of power supply options, we had to develop our own conversion method.
Once I came across two outwardly completely identical UPSs, but the manufacturer did not include two dozen parts on the board of one of them! In general, more than a dozen UPSs were rebuilt. The UPS with the TL494 PWM controller (or its corresponding analogues) succumbed to the alteration.
Conventionally, UPS can be divided into two categories:
— UPS of early release (without VSB and PS-ON pins), which do not start without load on the +5 V bus (I have often encountered cases of loading this bus with a 5 Ohm/10 W resistor, and this is an additional heat source in the UPS case), voltage stabilization -only via +5 V bus, start immediately after mains voltage is applied;
— UPSs of late release have VSB, PS-ON, PG, +3.3 V pins, a high level of stabilization on the +12 V bus and start only after the PS-ON pin is closed to the case (GND).
So, after opening the UPS, the first thing you need to do is clean it from dust. Then remove the cooling fan and lubricate it with machine oil; to do this, peel off the branded sticker and pick out the rubber plug.
We also remove the connectors for connecting the power cord and monitor, as well as the 115/230 V switch - an ammeter and an output voltage adjustment resistor will be placed in this place. The power cord should be soldered directly to the board. We replace the electrolytic capacitors on the +12 V bus with 25 V ones.
Solder the variable resistor
On the printed circuit board, solder a variable resistor Rreg to pin 1 of the TL494 PWM controller (Fig. 1 a or b - depending on the UPS version) and the common wire. resistance 47 kOhm. By decreasing the resistance of the resistor Rper, we are trying to increase the +12 V bus voltage, but at a voltage of 12.5 - 13 V, the UPS protection should trigger and it should turn off. This is responsible for the protection unit against exceeding the output voltage, usually starting with a zener diode (Fig. 2a or b - depending on the version of the UPS).
It must be found on the board and unsoldered for the duration of the experiments. If the zener diode is located elsewhere in the circuit, then you can find it by measuring the voltage drop across it (about 4 -5 or 10-12 V).
Next, we start the UPS and reduce the resistance of the resistor Rper. raise the voltage on the +12 V bus to the maximum (+16 - 20 V, depending on the specific UPS). On the board we solder all the resistors connected to pin 1 of the PWM controller and assemble the output voltage regulation circuit (Fig. 3).
Using resistor R2 we select the upper limit of adjustment (usually +16 V).
Let's return to protection against overvoltage.
There are two options:
— select a chain of low-power diodes connected in series with a zener diode (Figure 4a);
— assemble a circuit on a thyristor (Fig. 4b), the main condition of protection is operation at a voltage 1 - 1.5 V higher than the voltage of the upper control limit.
Next, to reduce acoustic noise, we connect a resistor with a resistance of 10 -15 Ohms and a power of 1 W in series with the positive wire of the fan (Fig. 5).
We mount the output terminals.
To improve the operation of the UPS, we include a chain of a resistor and two capacitors, according to the figure. We connect an ammeter to the gap in the positive (orange) wire.
I made a VHF power amplifier using the KT931 transistor, and to power it, a voltage of 20 - 27 V was required. I propose the option of connecting two UPSs into one (Fig. 6).
Everything here is simple, I won’t dwell on the details, the only thing is that in UPS 1 you must remember to cut the tracks to GND at the places where board 1 is attached to the case and install diodes VD1 - VD4. The ammeter is not shown in the figure.
A few weeks ago, for some experiment, I needed a constant voltage source of 7V and a current of 5A. Immediately I went in search of the required power supply in the utility room, but there was no such thing there. A couple of minutes later I remembered that I had found a computer power supply in the utility room, but this is an ideal option! Having thought about it, I gathered a bunch of ideas and within 10 minutes the process began. To make a laboratory constant voltage source you will need: - a power supply from a computer - a terminal block - an LED - a ~150 Ohm resistor - a toggle switch - heat shrink - cable ties A power supply may be found somewhere that is not needed. In case of targeted acquisition - from $10. I haven't seen anything cheaper. The remaining items on this list are cheap and not in short supply. Tools you will need: - glue gun a.k.a. hot glue (for mounting the LED) - soldering iron and related materials (tin, flux...) - drill - drill with a diameter of 5mm - screwdrivers - side cutters (nippers)Manufacturing
So, the first thing I did was check the functionality of this power supply. The device turned out to be working properly. You can immediately cut off the plug, leaving 10-15 cm on the side of the plug, because it may be useful to you. It is worth noting that you need to calculate the length of the wire inside the power supply so that it is enough to reach the terminals without tension, but also so that it does not occupy all the free space inside the power supply.
Now you need to separate all the wires. To identify them, you can look at the board, or rather at the pads to which they go. The sites must be signed. In general, there is a generally accepted color coding scheme, but the manufacturer of your power supply may have colored the wires differently. To avoid “misunderstandings” it is better to identify the wires yourself.
Here is my "wired gamma". If I'm not mistaken, this is the standard one. From yellow to blue, I think it’s clear. What do the bottom two colors mean? PG (short for “power good”) is the wire that we use to install the LED indicator. Voltage - 5V. ON is a wire that must be connected to GND to turn on the power supply. There are wires in the power supply that I did not describe here. For example, purple +5VSB. We will not use this wire, because... The current limit for it is 1A. As long as the wires do not interfere with us, we need to drill a hole for the LED and make a sticker with the necessary information. The information itself can be found on the factory sticker, which is located on one of the sides of the power supply. When drilling, you need to make sure that metal shavings do not get inside the device, because this can lead to extremely negative consequences.
I decided to install a terminal block on the front panel of the power supply. At home I found a block with 6 terminals, which suited me.
I was lucky because... The slots in the power supply and the holes for mounting the block coincided, and even the diameter was correct. Otherwise, it is necessary to either drill out the PSU slots or drill new holes in the PSU. The block is installed, now you can take out the wires, remove the insulation, twist and tin. I brought out 3-4 wires of each color, except white (-5V) and blue (-12V), because... there are one of them in the BP.
The first one is tinned - the next one is brought out.
All wires are tinned. Can be clamped into a terminal. Installing the LED I took an ordinary green indicator LED and an ordinary red indicator LED (as it turned out, it is somewhat brighter). We solder a gray wire (PG) onto the anode (the long leg, the less massive part in the LED head), onto which we pre-install heat shrink. We first solder a 120-150 Ohm resistor to the cathode (short leg, the more massive part in the LED head), and solder a black wire (GND) to the second terminal of the resistor, onto which we also do not forget to put heat shrink first. When everything is soldered, we slide the heat shrink over the LED leads and heat it.
It turns out this is the thing. True, I overheated the heat shrink a little, but that's not a big deal. Now I install the LED in the hole that I drilled at the very beginning.
I fill it with hot glue. If it is not there, you can replace it with super glue.
Power supply switch
I decided to install the switch in the place where the power supply wires used to go out. 
I measured the diameter of the hole and ran to look for a suitable toggle switch.
I did a little digging and found the perfect switch. Due to the difference of 0.22mm, it fit perfectly into place. Now all that remains is to solder ON and GND to the toggle switch, and then install it in the case.
The main work is done. All that remains is to clean up the mess. Wire tails that are not used must be insulated. I did it with heat shrink. It is better to insulate wires of the same color together.
We carefully place all the laces inside.
Screw the lid on, turn it on, bingo! With this power supply you can get many different voltages using potential differences. Please note that this technique will not work for some devices. This is the range of voltages that can be obtained. In brackets, the positive one comes first, the negative one comes second. 24.0V - (12V and -12V) 17.0V - (12V and -5V) 15.3V - (3.3V and -12V) 12.0V - (12V and 0V) 10.0V - (5V and -5V) 8.7V - (12V and 3.3V) 8.3V - (3.3V and -5V) 7.0V - (12V and 5V) 5.0V - (5V and 0V) 3.3V - (3.3V and 0V) 1.7V - (5V and 3.3V) -1.7 V - (3.3V and 5V) -3.3V - (0V and 3.3V) -5.0V - (0V and 5V) -7.0V - (5V and 12V) -8.7V - (3.3V and 12V) -8.3V - (-5V and 3.3V) -10.0V - (-5V and 5V) -12.0V - (0V and 12V) -15.3V - (-12V and 3.3V) -17.0V - (-12V and 5V) -24.0V - (-12V and 12V)
This is how we got a constant voltage source with short circuit protection and other goodies. Rationalization ideas: - use self-clamping terminals, as suggested here, or use terminals with insulated wings so as not to have to grab a screwdriver again.
Source: habrahabr.ru
samodelka.net
Where can I use a computer power supply?
Today it is not uncommon to find a computer power supply in a closet. Similar things are left over from old systems engineers, brought from work, and so on. Meanwhile, a computer power supply is not just junk, but a faithful household assistant! It is precisely what can be powered from a computer power supply that will be discussed today...
The car radio is powered from a computer power supply. Easily!
For example, you can power a car radio from a computer power supply. Thus getting a music center.
To do this, it is enough to correctly supply 12V voltage to the corresponding contacts of the car radio. And these same 12V are already available at the output of the power supply. To start the power supply, you need to close the Power ON circuit with the Ground (GND) circuit. This simple invention allows you to enjoy music in the garage without the need for a radio in your car. This means you won’t have to discharge the battery.
The same voltage can be used to check LED and incandescent lamps, which are intended for installation in a passenger car. The trick will not work with xenon lamps without modification.
www.mitrey.ru
How to make a welding inverter from a computer power supply with your own hands?
- 02-03-2015
- Tools required to make an inverter
- The procedure for assembling the welding machine
- Advantages of a welding machine from a computer power supply
A DIY welding inverter made from a computer power supply is becoming increasingly popular among both professionals and amateur welders. The advantages of such devices are that they are comfortable and lightweight.
Welding inverter device.
The use of an inverter power source allows you to qualitatively improve the characteristics of the welding arc, reduce the size of the power transformer and thereby lighten the weight of the device, makes it possible to make adjustments smoother and reduce spatter during welding. The disadvantage of an inverter-type welding machine is its significantly higher price than its transformer counterpart.
In order not to overpay large sums of money in stores for welding, you can make a welding inverter with your own hands. To do this, you need a working computer power supply, several electrical measuring instruments, tools, basic knowledge and practical skills in electrical work. It would also be useful to acquire relevant literature.
If you are not confident in your abilities, then you should go to the store for a ready-made welding machine, otherwise, with the slightest mistake during the assembly process, there is a risk of getting an electric shock or burning all the electrical wiring. But if you have experience in assembling circuits, rewinding transformers and creating electrical appliances with your own hands, you can safely begin the assembly.
Operating principle of inverter welding
Schematic diagram of the inverter.
The welding inverter consists of a power transformer that reduces the network voltage, stabilizer chokes that reduce current ripple, and an electrical circuit block. MOSFET or IGBT transistors can be used for the circuits.
The principle of operation of the inverter is as follows: alternating current from the network is sent to the rectifier, after which the power module converts direct current into alternating current with increasing frequency. Next, the current enters the high-frequency transformer, and the output from it is the welding arc current.
Return to contents
To assemble a welding inverter from a power supply with your own hands, you will need the following tools:
TL494 voltage feedback circuit in a computer power supply.
- soldering iron;
- screwdrivers with different tips;
- pliers;
- wire cutters;
- drill or screwdriver;
- crocodiles;
- wires of the required cross-section;
- tester;
- multimeter;
- consumables (wires, solder for soldering, electrical tape, screws and others).
To create a welding machine from a computer power supply, you need materials to create a printed circuit board, getinaks, and spare parts. To reduce the amount of work, you should go to the store for ready-made electrode holders. However, you can make them yourself by soldering crocodiles to wires of the required diameter. It is important to observe polarity when doing this work.
Return to contents
First of all, to create a welding machine from a computer power supply, you need to remove the power source from the computer case and disassemble it. The main elements that can be used from it are a few spare parts, a fan and standard case plates. It is important to take into account the cooling operating mode. This determines what elements need to be added to ensure the necessary ventilation.
Diagram of a transformer with primary and secondary windings.
The operation of a standard fan, which will cool the future welding machine from a computer unit, must be tested in several modes. This check will ensure the functionality of the element. To prevent the welding machine from overheating during operation, you can install an additional, more powerful cooling source.
To control the required temperature, a thermocouple should be installed. The optimal temperature for operating the welding machine should not exceed 72-75°C.
But first of all, you should install a handle of the required size on the welding machine from a computer power supply for carrying and ease of use. The handle is installed on the top panel of the block using screws.
It is important to choose screws that are optimal in length, otherwise too large ones may affect the internal circuit, which is unacceptable. At this stage of work, you should worry about good ventilation of the device. The placement of elements inside the power supply is very dense, so a large number of through holes should be arranged in it in advance. They are performed with a drill or screwdriver.
Next, you can use multiple transformers to create an inverter circuit. Typically, 3 transformers such as ETD59, E20 and Kx20x10x5 are chosen. You can find them in almost any radio electronics store. And if you already have experience creating transformers yourself, then it’s easier to do them yourself, focusing on the number of turns and the performance characteristics of the transformers. Finding such information on the Internet will not be difficult. You may need a current transformer K17x6x5.
Methods for connecting a welding inverter.
It is best to make homemade transformers from getinax coils; the winding will be enamel wire with a cross-section of 1.5 or 2 mm. You can use 0.3x40 mm copper sheet, after wrapping it in durable paper. Thermal paper from a cash register (0.05 mm) is suitable; it is durable and does not tear so much. The crimping should be done from wooden blocks, after which the entire structure should be filled with “epoxy” or varnished.
When creating a welding machine from a computer unit, you can use a transformer from a microwave oven or old monitors, not forgetting to change the number of turns of the winding. For this work, it would be useful to use electrical engineering literature.
As a radiator, you can use PIV, previously cut into 3 parts, or other radiators from old computers. You can purchase them in specialized stores that disassemble and upgrade computers. Such options will pleasantly save time and effort in searching for suitable cooling.
To create a device from a computer power supply, you must use a single-cycle forward quasi-bridge, or “oblique bridge”. This element is one of the main ones in the operation of the welding machine, so it is better not to save on it, but to purchase a new one in the store.
Printed circuit boards can be downloaded on the Internet. This will make recreating the circuit much easier. In the process of creating the board, you will need capacitors, 12-14 pieces, 0.15 microns, 630 volts. They are necessary to block resonant current surges from the transformer. Also, to make such a device from a computer power supply, you will need capacitors C15 or C16 with the brand K78-2 or SVV-81. Transistors and output diodes should be installed on radiators without using additional gaskets.
During operation, you must constantly use a tester and a multimeter to avoid errors and to assemble the circuit faster.
Electrical circuit of a semi-automatic welding machine.
After manufacturing all the necessary parts, they should be placed in the housing and then routed. The temperature on the thermocouple should be set to 70°C: this will protect the entire structure from overheating. After assembly, the welding machine from a computer unit must be pre-tested. Otherwise, if you make a mistake during assembly, you can burn all the main elements, or even get an electric shock.
On the front side, two contact holders and several current regulators should be installed. The device switch in this design will be a standard computer unit toggle switch. The body of the finished device after assembly requires additional strengthening.
Return to contents
A homemade welding machine will be small and light. It is perfect for home welding; it is convenient to weld with two or three electrodes, without experiencing problems with “flashing lights” and without worrying about the electrical wiring. The power supply for such a welding machine can be any household outlet, and during operation such a device will practically not spark.
By making a welding inverter with your own hands, you can significantly save on purchasing a new device, but this approach will require a significant investment of both effort and time. After assembling the finished sample, you can try to make your own changes to the welding machine from the computer unit and its circuit, to make lightweight models of greater power. And by making such devices for friends to order, you can provide yourself with a good additional income.
MoiInstrumenty.ru
Let's make a charger from a computer power supply
Many people, when purchasing new computer equipment, throw their old system unit into the trash. This is rather short-sighted, because it may still contain functional components that can be used for other purposes. In particular, we are talking about a computer power supply, from which you can make a charger for a car battery.
It is worth noting that the cost of making it yourself is minimal, which allows you to significantly save your money.
- 1 Charging from the computer's power supply
- 2 Rework process
- 3 Some nuances
Charging from the computer's power supply
The computer power supply is a switching voltage converter, respectively +5, +12, -12, -5 V. Through certain manipulations, you can make a completely working charger for your car from such a power supply with your own hands. In general, there are two types of chargers:
Chargers with many options (engine starting, training, recharging, etc.).
A device for recharging the battery - such charges are needed for cars that have a short mileage between runs.
We are interested in the second type of chargers, because most vehicles are used for short distances, i.e. the car was started, driven a certain distance, and then turned off. Such operation leads to the car battery running out of charge quite quickly, which is especially typical in winter. Therefore, such stationary units are in demand, with the help of which you can very quickly charge the battery, returning it to working condition. The charging itself is carried out using a current of about 5 Amps, and the voltage at the terminals ranges from 14 to 14.3 V. The charging power, which is calculated by multiplying the voltage and current values, can be provided from the computer power supply, because its average power is about 300 -350 W.
Converting a computer power supply into a charger
Rework process
Before proceeding with the list of certain modifications to the computer's BM, you need to keep in mind that its primary circuits contain a rather dangerous voltage that can harm human health.
Therefore, you need to pay close attention to basic safety standards when working with this device.
So, you can get to work. We take your existing power supply of the required power (in our case, we are considering the PSC200 model, whose power is 200 W). Let us describe the entire algorithm of actions step by step:
- First you need to remove the cover from the computer's power supply by unscrewing several bolts. Next you need to find the core of the pulse transformer.
- Next, you need to measure this core, and multiply the resulting value by two. This value is individual; using the device in question as an example, the value obtained was 0.94 cm2. In practice, it is known that 1 cm2 of a core is capable of dissipating about 100 W of power, i.e. our unit is quite suitable (based on the calculation - 14 V * 5 A = 60 W needed to charge the battery).
- The power supplies use a fairly standard TL494 chip, common to many models.
We only need +12 V circuit elements. Therefore, everything else just needs to be unsoldered. For convenience, two diagrams are shown - on one, a general view of the microcircuit, and on the second, the circuits that need to be desoldered are highlighted in red:
In other words, we are not interested in the -5, +5, -12 V circuits, as well as the start signal circuit (Power Good) and the 110/220 V voltage switch. To make it even clearer, let’s highlight the piece that interests us:
R43 and R44 are reference resistors. The value of R43 can be adjusted, which allows you to change the value of the output voltage on the +12 V circuit. This resistor must be replaced with a constant resistor R431 and a variable resistor R432. The output voltage can be adjusted within 10-14.3 V, and the current passing through the battery can be adjusted.
Additionally, we suggest looking at converting an ATX power supply into a charger
The capacitor located at the output of the +12 V circuit rectifier was also replaced. In its place, a capacitor with a higher voltage rating was installed (in our case, C9 was used).
The resistor located next to the blower fan must be replaced with a similar one, but with a slightly higher resistance.
The fan itself must be positioned in such a way that the air from it flows inside the power supply unit, and not outside, as was the case before. To do this, rotate it 180 degrees.
It is also necessary to remove the tracks that connect the mounting holes of the board to the chassis and the ground circuit.
It is worth noting that the resulting charger from the power supply must be connected to an alternating current network through an ordinary incandescent lamp with a power of 40 to 100 W.
This must be done at the stage of assembly and performance testing, then there is no need for this. This is necessary so that nothing in our power supply burns out due to power surges.
When selecting the ratings of R431 and R432, it is necessary to monitor the voltage in the Upit circuit - it should not exceed 35 V. The optimal indicators, in our case, will be an output voltage of 14.3 V with a low resistance of resistor R432.
Another modification option
Some nuances
After testing our homemade power supply charger in operation, you can add some useful little things to it.
To see the charge level clearly, you can install pointer-type or digital indicators in this charger. In our case, we used two devices with arrows from old tape recorders. The first will show the charging current level, and the second will show the voltage at the battery terminals.
In principle, this completes the assembly process. Some craftsmen complement it with other decorations (LED indicators, an additional case with handles, etc.), but this is not at all necessary, because the main purpose of this device is to charge the car battery, which it successfully does.
The feasibility of making your own charger from a computer power supply can hardly be questioned, because in this case there are practically no monetary costs.
The only caveat is that self-assembly from a power supply is not accessible to everyone, because you need to have a good understanding of electronics in order to competently and consistently complete the entire assembly.
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generatorexperts.ru
Adjustable power supply 2.5-24V from the computer's power supply
In contact with
How to make a full-fledged power supply yourself with an adjustable voltage range of 2.5-24 volts is very simple; anyone can repeat it without any amateur radio experience. 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, every home has already accumulated a sufficient amount of old computer hardware and a power supply unit is probably also there, so the cost of homemade products will be insignificant, and for some masters it will be zero rubles .
I got this AT block for modification.
The more powerful you use the power supply, 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, the output voltage drops completely. Look what is written on the case.
Therefore, see for yourself what kind of current you plan to receive from your regulated power supply, this potential of the donor and lay it in right away. There are many options for modifying a standard computer power supply, but they are all based on a change in the wiring of the IC chip - TL494CN (its analogues DBL494, KA7500, IR3M02, A494, MV3759, M1114EU, MPC494C, etc.). 
Fig No. 0 Pinout of the TL494CN microcircuit and analogues. Let's look at several options for designing computer power supply circuits, perhaps one of them will be yours and dealing with the wiring will become much easier.
Scheme No. 1. 
Let's get to work.
First you need to disassemble the power supply housing, unscrew the four bolts, remove the cover and look inside. 
We are looking for a microcircuit on the board from the list above, if there is none, then you can look for a modification 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 wiring and the location of unnecessary parts that need to be removed. 
For ease of operation, first completely unscrew the entire board and remove it from the case. 
In the photo there is a 220v power connector. Let's 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 immediately when plugged into the outlet. If the unit is ATX, 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 a switch in the gap of this wire. 
Now you need to look at how many volts the large output capacitors cost, if they say less than 30v, then you need to replace them with similar ones, only with an operating voltage of at least 30 volts. 
In the photo there are black capacitors as a replacement option for the blue one. This is done because our modified unit will produce not +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; increasing it is always recommended.
The most important part of the job.
We will remove all unnecessary parts in the IC494 harness and solder other nominal parts so that the result is a harness like this (Fig. No. 1).Fig. No. 1 Change in the wiring of the IC 494 microcircuit (refinement circuit). We will only need these legs of the microcircuit No. 1, 2, 3, 4, 15 and 16, do not pay attention to the rest. 
Rice. No. 2 Option for improvement using the example of diagram No. 1 Explanation of symbols. 
You need to do something like this: we find leg No. 1 (where the dot is on the body) of the microcircuit and study what is connected to it, all circuits must be removed and disconnected. Depending on how the tracks will be located and the parts soldered in your specific modification of the board, the optimal modification option is selected; this may be desoldering 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 remodeling process according to the revision scheme. 
The photo shows replacing resistors with the required value. 
In the photo - by lifting the legs of unnecessary parts, we break the circuits. Some resistors that are already soldered into the wiring diagram can be suitable without replacing them, for example, we need to put a resistor at R=2.7k with a connection to the “common”, but there is already R= 3k connected to the “common”, this suits us quite well and we leave it there unchanged (example in Fig. No. 2, the green resistors do not change). 
On the photo, we cut the tracks and added new jumpers, write down the old values with a marker, it may be necessary to restore everything back. Thus, we look through and redo all the circuits on the six legs of the microcircuit. This was the most difficult point in the rework.
We make voltage and current regulators.
We take variable resistors of 22k (voltage regulator) and 330Ohm (current regulator), solder two 15cm wires to them, solder the other ends to the board according to the diagram (Fig. No. 1). Install on the front panel. Voltage and current control.
To 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: www.ebay.com) 
I used my own ammeter, from old USSR stocks.
IMPORTANT - inside the device there is a Current resistor (Current sensor), which we need according to the diagram (Fig. No. 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 a homemade RC is made, a wire D = 0.5-0.6 mm is wound around a 2-watt MLT resistance, turn to turn for the entire length, solder the ends 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 scraps, they are easier to drill and cut. 
On the front board we place devices, resistors, regulators, and sign the designation. 
We make the sides and drill them. 
We drill mounting holes, assemble, and fasten with screws. 
Small legs are obtained by processing the laminate on a sharpener. 
The assembled device, we will check what happened. Let's see a little test.
There is a lot of information on the Internet about converting ATX-AT computer power supplies into laboratory power supplies and chargers. I have read dozens of articles about conversions, but there is practically no information about self-assembly from parts of these same PC power supplies. 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-handed PWM, it can always be replaced with a TL494, on a neat new board. And most importantly, your payment
My ATX 400W power supply burned out. I added him to five more brothers, and realized that I needed to do something with them. I decided to start with the extreme 400W power supply; I was attracted by its two 12V buses 12A and 15A, which gave a total of 27A. But it turned out that both buses are connected to one 12V output and it’s unlikely that the required Amps will be collected there. But maybe I’ll get at least 20A, I thought, and decided to assemble a power supply.
Assembly conditions:
- make AT from ATX
- universal board for further modifications
- minimum details
— we only sew TL494
— voltage stabilization 12V, 14.4V and current up to 20A
Having searched online for AT power supply diagrams, I chose the diagram and modified it a little
I didn't do anything special to the block.
— Eliminated unnecessary wiring 5V 3.3V, etc.
— Remade 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 to TL494. One thing that bothered me was what frequency the donor was working at. But then it turned out that the frequency calculation formula for the 3528 is the same as for the TL494 F=1.1/RC. According to the scheme, the frequency is 73 kHz
I began to pay the fee. After hours of torment, the result was this board.
The board is currently final and has never been assembled. The first version of the board is a little lighter, it does not have circuits around the error amplifiers, but control is carried out from another board through an optocoupler transistor from the 14th Vref leg to the 4th DT leg. The second version eliminates the optocoupler and control is carried out through dividers on an additional board, through TL494 legs 1,2,3,15,16. The first and second versions of the power supply board are working and one hundred percent tested. Therefore, be careful to check the new version of the board before production. If there are errors, write through the form, I will correct everything.
And a few words about the launch. went through the traditional 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. The voltage dropped by 0.2V
When connecting 14.4V stabilization to the load it gave 8.4A, the voltage dropped by 0.2V. Unfortunately I didn't take a photo.
It also responds normally to current limitation. I haven’t loaded it with more than 10A yet, nothing to do with it. No photo yet
Well, a couple more photos of the assembled board before the first tests
Video of the assembled power supply - ATX charger
That's all for now. Next photos and updates as time permits
With uv. Admin check
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:
- disassemble and rewind for specific voltages;
- solder the windings in series, adjusting the output voltage using PWM
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 the wrong 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 :)
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