Do anyone know how to convert atx psu to varible power supply?

Alec_t

Joined Sep 17, 2013
12,456
on mine psu there are 4 optocouplers so those that mean that i should bridge all of them or i should bridge the one that is responsable for the safty future
Without a schematic and an understanding of the circuit it would not be safe to bridge any of them.
A problem with simply varying the output voltages (they are probably all arranged to vary in unison with a common preset adjustment) is that the voltage or current ratings of certain components will be exceeded, risking destruction/fire.
 

Papabravo

Joined Feb 24, 2006
17,562
Now the only remaining problem is to verify that the DTK schematic is close to or identical to the one possessed by the TS. In particular the TS mentioned that his supply was old. To me that means no 3.3 VDC section. There is still the problem of identifying all the resistors connected to pin 2 of the TL494.
 
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Thread Starter

Dzoro

Joined Feb 1, 2019
194
The output rails are 3.3v 19A 5v24A 12v8A also it has like any other atx -12 and on the old ones -5 that is the white wire.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
And for the ressistors pin 2 is going to a voltage devider of two 4k7 ressistors.One ressistor goes to gnd and the other one is going to pins 15,14,13
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
Yes it's easy with a TL494, you need to ground pin 4 to override the cutout, then pins 1,2 are for votage regulation control.


http://www.pavouk.org/hw/en_atxps.html


Pin 1 is the reference input, and Pin 2 is the output feedback pin, looking at this diagram they have set the output using fixed resistors on pin 2. If you remove all resistors on pin 2, and connect a 10K potentiometer across the 12V rail (yellow black) and put the wiper to pin 2, you will have a Variable output.

If all is working it should go from 5V to 28V on the 12V rail, replace the output capacitors to 35V or 63V..
I saw the chematic and mine is very similar to yours
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
And i need just to diseable the safty future when i lower the ressistance on the pot it's turning itself off.
And that as i saw can be achiwed by bridging the optocoupler on the primary side
Guide me if i am wrong
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
WRONG!! You need to ground pin 4 to 7, this disables the shutdown, like i said in post #20.
The both methodes work i tryed the thing that you sead and now i have varible psu.
Just one more question.
Every atx have +12 and -12 and when they are combined i get 24 volts on my multimeter so can i make it so varies the output from 0 to 24 or is it going to be just from 12 to 24
 

Dodgydave

Joined Jun 22, 2012
10,139
If you have +12vand -12v, you wont be able to draw over 1amp on the -12v rail, so a combination of both of them will give a total variable voltage of approx 9V to 55V .
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
If you have +12vand -12v, you wont be able to draw over 1amp on the -12v rail, so a combination of both of them will give a total variable voltage of approx 9V to 55V .
That is quite reasonable for me beacose for high voltage i wont exceed 1A
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
And also thank you for the help i realy wanted varible atx and with your help i achived what i wanted thanks a lot :):)
 

Papabravo

Joined Feb 24, 2006
17,562
Yes and i know how to build an ajustable switcher
For example i could use two lm371 one to regulate the voltage and one to regulate the current.I could use biger transistor on the current side beacose lm 371 can output 1A and i use more than 1A in my projects and i don't even have to spend money beacose i have all this components in my workbench beacose i work with electronics for 4 years and i ghaterd a lot of components over the years
I have a lot of knowlege about some circuits like that but i wanted to do something whit the main chip of the psu and i found this on the internet
Did you mean LM317. I don't think LM371 exists as a common part.
 

MisterBill2

Joined Jan 23, 2018
10,500
Unless things have changed a lot, using a computer power supply required adding a load resistor to the 5 volt line to draw quite a few amps, perhaps 5 amps. Then the other two terminals to connect to make it start. At that point you have +5 volts, +3.3 volts, and +12 volts ate worth while power levels, and negative voltages, -5 and -12, at much lower power levels. Adjusting the supply may be a challenge without some clue as to what resistors to change.
But having the three voltages available will make a lot of experimenting possible.
AND, No insults or criticisms from me! The method I describe has been repeated lots of times with all sorts of claims, and it seems reasonable.
And since all computer power supplies are switchmode, adjusting them is not simple to figure out.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
194
Unless things have changed a lot, using a computer power supply required adding a load resistor to the 5 volt line to draw quite a few amps, perhaps 5 amps. Then the other two terminals to connect to make it start. At that point you have +5 volts, +3.3 volts, and +12 volts ate worth while power levels, and negative voltages, -5 and -12, at much lower power levels. Adjusting the supply may be a challenge without some clue as to what resistors to change.
But having the three voltages available will make a lot of experimenting possible.
AND, No insults or criticisms from me! The method I describe has been repeated lots of times with all sorts of claims, and it seems reasonable.
And since all computer power supplies are switchmode, adjusting them is not simple to figure out.
I did manage to get varible output frok my atx psu with help from dodgydave
 
I would like to convert my old atx power supply to give varible output but i don't want to put buck or boost converter or some other pcb in it.
It will be easier to make water flow up hill in attempt to modify an ATX power supply, it would also be easier designing a new power supply to achieve what you are asking.
 

MisterBill2

Joined Jan 23, 2018
10,500
I achived what i asked for
OK, if you were able to add an adjustment function to this power supply I would very much appreciate if you would share that information. My examination of several computer power supplies left me thinking that I had no idea as to where to add an adjusting function. So if you can provide any information I would really appreciate it.
 
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