Modifying an ATX power supply

[boylesg]

How practical is it to modify only the 12V output of an ATX power supply such that it is adjustable to any voltage from say 5V to 12V?

Am am envisaging replacing a fixed resistor with a 25 turn trim pot.

 

[KlausST]

Hi,

If it is a flyback, then it may become difficult, because there is only one regulation loop, for all output voltages in common.
If one voltage becomes smaller, all others will follow.

Klaus

 

[andre_luis]

...moreover, not infrequently the feedback resistor is on the high frequency side of the switching circuit, so that its replacement by a trimpot would surely cause EMI issues. By the way, it is more certain that the 5V is the reference voltage for the others, so that in order to adjust the 12V you would have to handle with the 5V circuitry.

 

[Relayer]

Hello boylesg,
Check this place out:

ATX Mods

I haven't personally tried doing what the guy suggests in the link, but I have used
another modder to raise my output to 16 volts to which I need for a DCC controller,
which boosts the output current on a model train controller.
The only stipulation is that the PSU you want to modify, MUST have a SMPS Controller
IC either TL494 or the Korean clone KA7500.
I hope the above helps.
Regards,
Relayer

 

[FvM]

Check this place out

The article is about converting an ATX device into a single output variable voltage supply. That should work under circumstances.

But it's not possible to make the 12V output variable and keep the 3.3 and 5V output, at least not without adding a buck converter.