PROJECT No. 20: power supply with adjustable Uout from an ATX block
I have repeatedly paid attention to recommendations on the Internet for converting computer power supplies into laboratory ones with adjustable output voltage. And so I decided to try to upgrade the ATX unit with minimal intervention in the circuit. Because I've accumulated enough stuff RADIOshabara, then financial costs should be minimal.
1. I took the ATX block out of storage:
2. It says: 
I am somewhat skeptical about these parameters. But God be with them, with the parameters. I will be quite satisfied if they are at least half correct.
3. Don’t forget to turn on the unit from the rear: 
according to the color coding of the power connector 
closed the green wire “PsON” and the black wire “Gnd” - the unit turned on: 
4. I checked the voltages at the +12V and +5V outputs: 
5. I begin the autopsy. I sweep away dust and other debris with a brush: 
6.Disconnect the input ~
220V, unscrew the screws securing the board and fan and remove them from the case: 
7. I unsolder the extra wires and the fan (for now, so as not to interfere): 
8. I’m trying to determine which PWM controller is in this block. The inscription is difficult to read: KA7500V 
9. Bottom view of the controller wiring: 
10. Remaking the power supply is quite simple - you need to find a resistor R34
(shown by an arrow) connecting the 1st leg of the microcircuit and the +12V bus, and unsolder it: 
It is also highlighted in the diagram yellow:
True, the nominal value on the diagram is 3.9 kOhm, and measurements show that not everything that is written on the diagram is true... In reality, the resistance of this resistor was about 39 kOhm. 
11. In place R34
you need to solder a variable resistor. Without bothering myself with a long search, I took a 47 kOhm + 4.3 kOhm variable in series with it (I believe you can use slightly different values): 
12. Turned on the power supply - nothing unnecessary sounds, odors, sparks, fires, etc. – it worked immediately: 
13. Measured the ranges of voltage changes: 
+12V: 4.96…12.05V
+5V: 2.62…5.62V
+3.3V: 1.33…3.14V
This suits me, since I did not set any GLOBAL goals for upgrading this power supply.
14. To indicate the output voltage, I will use a regular analog voltmeter: 
His readings agree quite well with the digital ones: 
15. The block must be given the appearance of a finished structure. I think that the PSU case is already good enough. Only the front panel will have to be decorated. To do this, I will connect terminals and a switch to it (I just want to say “TUMBLE SWITCH type” by analogy with the “SORTER type” toilet located strictly to the north, indicated on the plan by the letters “ME” and “JO” - see photo from my favorite comedy ), 
voltmeter, ammeter and, of course, LED.
Like that: 
However, as an estimate showed, I had gone too far. I don’t have enough miniature instruments, so there’s nowhere to put an ammeter! And if you install it, then there will be no place to place all the other elements, if you make the front panel no larger than the actual size of the front side of the block.
This is how it looks in FrontDesigner 3.0. You can download it from HERE, or you can search it on the Internet. 
16. After thinking a little, I decided to replace the previous voltmeter with another one that I wouldn’t mind redoing. This voltmeter is also designed to work in a horizontal position, and if it is placed vertically, the scale angle will be negative - this is not very convenient for observations. This is the device I will modernize a little. 
The device is open: 
I measure the resistance of the additional resistor: 
The new measurement limit will be 15V. Based on the fact that the voltage U is proportional to the resistance R (and vice versa), i.e. according to Ohm's law for the section of the circuit U=IR and R=U/I, a simple proportion follows Rd/x=6V/15V, from which x=Rd×15/6, where Rd=5.52 kOhm is the old additional resistor, x is the new one additional resistor, 6V – previous limit, 15V – new voltmeter limit.
So, x = 5.52x15/6 = 13.8 kOhm. This is elementary physics and mathematics.
I made up a new resistor from two: 
The body of the device had to be “shortened” somewhat to match the height of the power supply: 
I made a new scale in the same FrontDesigner 3.0 program. The voltmeter will have to work in extreme conditions: upside down and vertically, and the countdown will be “reverse” - from right to left! 
17. This is approximately how everything will be located on the front panel: 
I mark the panel: 
And I make holes in it: 
I install the elements: 
The panel will be attached to the PSU case using U-shaped brackets: 
Looking out the window, I discovered that, as always, the first snow had unexpectedly fallen - Oct 26, 2016: 
18. I begin final assembly. Once again I estimate the placement: 
I first install the voltmeter and the front panel on the PSU case: 
I inserted the fan in reverse so that it would blow air inside the case, inserted the board, connected “GND”, the switch (“PsON” and “Gnd”), turned it on - the power supply started up. The output voltage is also adjusted in the opposite direction - counterclockwise. I checked the voltage change on the +12V bus: 
I soldered all the wires, installed and connected the voltmeter, installed the front panel, turned it on - the LED blinked, the voltmeter needle jumped to the left (I have it installed “in reverse”) and that’s it! Turned it off, turned it on - the same thing! I checked if there were any short circuits on the back of the front panel - everything was fine. What's the matter? I turned the variable resistor down (it was at maximum), turned it on, and the power supply started working. I smoothly rotate the regulator - everything is fine again: the voltage at the outputs increases and decreases, the unit does not turn off. Turned it off. Turned it up to maximum, turned it on - it won’t turn on again! Turned it off. I set it to an intermediate position, turned it on - the power supply started up. That. The error is not in the installation, but somewhere deeper. But the power supply works! 
I finally assemble the structure and turn it on again to check: 
Here is the finished design: 
I'll call it "BP-ATX v2.0".
Financial costs are ZERO. I only used parts and materials that I had.
The computer serves us for years, becomes a true family friend, and when it becomes outdated or hopelessly breaks down, it is such a pity to take it to the landfill. But there are parts that can last a long time in everyday life. This and
numerous coolers, a processor radiator, and even the case itself. But the most valuable thing is the power supply. Thanks to its decent power and small dimensions, it is an ideal object for all kinds of modernizations. Transforming it is not such a difficult task.
Converting a computer into a regular voltage source
You need to decide what type of power supply your computer has, AT or ATX. As a rule, this is indicated on the body. Switching power supplies only work under load. But the design of the ATX type power supply allows you to artificially imitate it by shorting the green and black wires. So, by connecting the load (for AT) or closing the necessary terminals (for ATX), you can start the fan. The output appears 5 and 12 Volts. The maximum output current depends on the power of the power supply. At 200 W, at a five-volt output, the current can reach about 20A, at 12V - about 8A. So, without extra costs, you can use a good one with good output characteristics.
Converting a computer power supply into an adjustable voltage source
Having such a power supply at home or at work is quite convenient. Changing a standard block is easy. It is necessary to replace several resistances and remove the inductor. In this case, the voltage can be adjusted from 0 to 20 Volts. Naturally, the currents will remain in their original proportions. If you are satisfied with the maximum voltage of 12V, it is enough to install a thyristor voltage regulator at its output. The regulator circuit is very simple. At the same time, it will help to avoid interference with the inside of the computer unit.
Converting a computer power supply into a car charger
The principle is not much different from a regulated power supply. It is only advisable to change to more powerful ones. A charger from a computer's power supply has a number of advantages and disadvantages. The advantages primarily include small dimensions and light weight. Transformer chargers are much heavier and more inconvenient to use. The disadvantages are also significant: criticality to short circuits and polarity reversal.
Of course, this criticality is also observed in transformer devices, but upon failure pulse block alternating current with a voltage of 220V tends to the battery. It’s scary to imagine the consequences of this for all devices and people nearby. The use of protection in power supplies solves this problem.
Before using this charger, take the design of the protection circuit seriously. Moreover, there are a large number of their varieties.
So, don’t rush to throw away spare parts from your old device. Remaking a computer power supply will give it a second life. When working with a power supply, remember that its board is constantly under 220V voltage, and this poses a mortal threat. Follow personal safety rules when working with electric current.
Regulated power supply from an ATX computer power supply
If you have an unnecessary power supply from an ATX computer, then it can be easily turned into a laboratory switching regulated power supply, with regulation of not only voltage, but also current, which means that it can be used, for example, for charging or restoring batteries.
The power supply has the following parameters:
- Voltage - adjustable, from 1 to 24V
- Current - adjustable, from 0 to 10A
Any block is suitable for conversion ATX power supply, assembled on a TL494 PWM controller. An analogue of this microcircuit, the KA7500, is often used in power supplies.
The circuits of most power supplies are similar, and even if you couldn’t find a circuit diagram specifically for yours, that’s okay. The primary task is to remove the secondary circuits from the board after power transformer, as well as circuits that control the operation of the TL494 chip. In the diagram below, these areas are highlighted in red. Before soldering, mark the terminals of the secondary winding of the power transformer along the 12 volt bus. We'll need them.
Click on the diagram to enlarge
This will free up a lot of space on the board. Printed tracks can also be removed by running a heated soldering iron over them. Some printed tracks coming from the pins of the microcircuit, which we will use later, can be left for convenience and soldered to them.
Now it is necessary to assemble new output circuits and current and voltage control circuits. An assembly of two Schottky diodes with a common cathode must be soldered to the previously marked windings of the 12-volt bus transformer. The assembly can be taken from the +5V bus, usually it has the following parameters: voltage - 30V, current - 20A. Schottky diodes have a very low voltage drop, which is important in this case. At this type The rectifier can power most loads.
If you need high current at maximum voltage, this option not enough. In this case, it is necessary to remove the middle point of the transformer, and make the rectifier from four diodes according to the classical scheme.
Then you need to wind the choke. To do this, you need to take the soldered group stabilization choke and wind all the windings from it. The throttle core is yellow, one end side is painted white. It is necessary to wind 20 turns on this ring with two wires with a diameter of 1 mm in parallel. If there is no such thick wire, then you can connect several strands of thinner wire together and wind them in parallel. With this winding, all leads at both ends of the winding must be tinned and connected. A choke with such parameters will provide a current of about 3A. If you need more current, then the inductor should be wound with ten parallel wires with a diameter of 0.5 mm.
After this, you can begin assembling that part of the circuit that is responsible for the adjustments. The authorship of this method belongs to the user DWD, link to the discussion topic:
http://pro-radio.ru/power/849/
The adjustment is very simple. Consider the voltage regulation circuit. A voltage divider with two resistors is connected to the comparator input (pin 1) of the TL494 microcircuit. The voltage at their midpoint should be approximately 4.95 volts. If you want to change the upper limit of power supply voltage regulation, you need to recalculate this divisor. The second input of the comparator (pin 2) is connected to the midpoint of the variable resistor, thus also creating a voltage divider. If the voltage at pin 1 of the comparator is less than the voltage at pin 2, then the microcircuit will increase the pulse width until the voltages are equalized. This is how the output voltage of the power supply is adjusted.
Current regulation works similarly, only here the voltage drop across the shunt Rsh is used to control the current flowing in the load. Almost any shunt with a resistance of 0.01-0.05 Ohm can be used as a shunt, for example, a section of a conductive path, a shunt from a milliammeter, or several SMD resistors. The upper limit of adjustment is set by a tuning resistor with a resistance of 1 kOhm. If adjustment of the upper limit is not needed, then this resistor should be replaced with a constant resistance of 270 Ohms, which will provide adjustment up to 10A.
A photo of the power supply is shown below. On the front panel there is an ampere-voltmeter screen, under which there are knobs for voltage and current regulators. The output terminals are made of RCA sockets glued inside with epoxy. It is very convenient to attach alligator clips to such terminals. The large yellow LED is an indicator that the power supply is turned on, which is carried out by the large red switch.
Due to the fact that the case chosen for the power supply is very compact (16*12cm), the installation turned out to be dense with an abundance of wires. In the future, the wires can be assembled into bundles.
To cool the power supply, a thermostat is used on the K157UD1 microcircuit, which cools the assembly of Schottky rectifier diodes and turns on automatically as needed, then turns off. Its design will be discussed separately.
If you have an old computer power supply (ATX) at home, you shouldn’t throw it away. After all, it can be used to make an excellent power supply for home or laboratory purposes. Minimal modification is required and in the end you will get an almost universal power source with a number of fixed voltages.
Computer power supplies have a high load capacity, high stabilization and short circuit protection.
I took this block. Everyone has such a plate with a number of output voltages and maximum load current. The main voltage for constant operation is 3.3 V; 5 V; 12 V. There are also outputs that can be used for a small current, these are minus 5 V and minus 12 V. You can also get the voltage difference: for example, if you connect to “+5” and “+12”, then you get a voltage of 7 V. If you connect to “+3.3” and “+5”, you get 1.7 V. And so on... So the voltage range is much larger than it might seem at first glance.
Pinout of computer power supply outputs
The color standard is, in principle, the same. And this color connection scheme is 99 percent suitable for you too. Something may be added or removed, but of course everything is not critical.
The rework has begun
What do we need?- - Screw terminals.
- - Resistors with a power of 10 W and a resistance of 10 Ohms (you can try 20 Ohms). We will use composites of two five-watt resistors.
- - Heat shrink tube.
- - A pair of LEDs with 330 Ohm quenching resistors.
- - Switches. One for networking, one for management
Computer power supply modification diagram
Everything is simple here, so don't be afraid. The first thing to do is to disassemble and connect the wires by color. Then, according to the diagram, connect the LEDs. The first one on the left will indicate the presence of power at the output after switching on. And the second one from the right will always be on as long as the mains voltage is present on the block.
Connect the switch. It will start the main circuit by shorting the green wire to common. And turn off the unit when opened.
Also, depending on the brand of the block, you will need to hang a 5-20 Ohm load resistor between the common output and plus five volts, otherwise the block may not start due to the built-in protection. Also, if it doesn’t work, be prepared to put the following resistors on all voltages: “+3.3”, “+12”. But usually one resistor per 5 Volt output is enough.
Let's get started
Remove the top cover of the casing.We bite off the power connectors going to motherboard computer and other devices.
We untangle the wires by color.
Drill holes in the back wall for the terminals. For accuracy, we first go through with a thin drill, and then with a thick one to match the size of the terminal.
Be careful not to get any metal shavings on the power supply board.
Insert the terminals and tighten.
We put together the black wires, this will be common, and strip them. Then we tin it with a soldering iron and put on a heat-shrinkable tube. We solder it to the terminal and put the tube on the solder and blow it with a hot air gun.
We do this with all the wires. Which you don’t plan to use, bite them off at the root of the board.
We also drill holes for the toggle switch and LEDs.
We install and fix the LEDs with hot glue. Solder according to the diagram.
We place the load resistors on the circuit boards and screw them in with screws.
Close the lid. We turn on and test your new laboratory power supply.
It would be a good idea to measure the output voltage at the output of each terminal. To be sure that your old power supply is fully functional and the output voltages are not outside the permissible limits.
As you may have noticed, I used two switches - one is in the circuit, and it starts the block. And the second, which is larger, bipolar, switches the input voltage of 220 V to the input of the unit. You don't have to install it.
So friends, collect your block and use it to your health.
Watch a video of making a laboratory block with your own hands
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 put electrolytic capacitors voltage exceeding 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. Datasheet and Google help better than forums, if you have advanced “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 schemes from powerful car amplifiers low frequency - 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!
Loading...
