I want to turn a PSU into a variable power supply, I need the schematics/parts list to do so.

Ideally I want to drop the 450v or so from the capacitors to 100v (the max my digital voltmeters can read) and have that variable from 0-100 volts.

If that is not possible, I'd like to have a 24v variable source (would taking two 12v lines in series work in a PSU?) from 0-24v.

And, if that does not work, I want to make 12v variable from 0-12v.


I am looking for simple schematics I can make on a breadboard (can't print circuit boards), and need to be fairly small, and a full parts list.

I have an xl file here with all the parts I have salvaged from other PSUs, would any of those voltage regulators work?

 

What kind if "PSU" do you have ?

 

What kind if "PSU" do you have ?

just an ordinary desktop one. I've been making them into bench PSUs for quite some time but never variable ones.

 

Gee Whizz.. where do you get 450 Volts across capacitors from?

 

I want to turn a PSU into a variable power supply, I need the schematics/parts list to do so.

It's almost impossible to get the schematics of ATX power supplies and it's dangerous to start modifying them if, as it sounds, you don't really know what you are doing.

Ideally I want to drop the 450v or so from the capacitors to 100v (the max my digital voltmeters can read) and have that variable from 0-100 volts.

The mains is rectified as soon as it enters the power supply so on 240VAC you get approximately 340VDC across the capacitors. This voltage can give you quite a kick so care is needed. Why would you want to make this variable? I think it's time you bought a new DMM as well?

If that is not possible, I'd like to have a 24v variable source (would taking two 12v lines in series work in a PSU?) from 0-24v.

No. All the 12V rails come from the same source.

And, if that does not work, I want to make 12v variable from 0-12v.

Modifying the power supply isn't feasible so you could leave the power supply alone and add extra circuitry outside the box to make the 12V rail varible although the best you could get out is probably 10~10.5V.

I am looking for simple schematics I can make on a breadboard (can't print circuit boards), and need to be fairly small, and a full parts list.

I have an xl file here with all the parts I have salvaged from other PSUs, would any of those voltage regulators work?

Your XL file is empty!

You're better off leaving the ATX power supply well alone and building from scratch.

 

Gee Whizz.. where do you get 450 Volts across capacitors from?

I've seen some with that much for the caps, but I opened the one I have and it only has 200v for the caps (probably just older ones have higher voltage) so that makes it easier.

Your XL file is empty!

You're better off leaving the ATX power supply well alone and building from scratch.

Eh, supposed to be xml, anywys dropbox messed it up I guess.

And I'm not talking about schematics for the power supply itself, I'm talking about a variable voltage regulator circuit I can hook the 12v or whatever from the power supply into.

Also I said digital voltmeter, not multimeter. I am using a digital voltmeter as a display for the voltage,search them on ebay and you'll see.

Also in the many power supplies I have taken apart I have not seen one that uses the capacitors to recity the AC (120 in my area fyi), and even if they do, I don't think this one does because there are a couple diode bridges before the capacitors.

 

Basic Bench Top Power Supplies

 

Basic Bench Top Power Supplies

Ahh, that schematic is great, are you aware of a voltage regulator that can take up to 100 volts? (and one that is not variable that would limit 200v to 100).

 

Are you trying to regulate 450V down to 12V?

Sorry, it is not clear to me.

 

Are you trying to regulate 450V down to 12V?

Sorry, it is not clear to me.

No, a power supply has 12v, 5v and 3.3v outputs, but I'd like to have a variable one as well. The power supply which I have has 200v on the caps, I need to halve that and then use a variable voltage regulator so that I can have a variable output from 0-100v.

 

I want to turn a PSU into a variable power supply, I need the schematics/parts list to do so.
...
If that is not possible, I'd like to have a 24v variable source (would taking two 12v lines in series work in a PSU?) from 0-24v.
...

If your current doesn't need that much, you can using +12V and -12V → LM317 → 21V (Adjustable), if you want to get some more voltages, then you need to adjust inside of PSU.

If you need more current then you can using two atx power as +12V-0V in series with +12V-0V → LM338 → 21V (Adjustable), if you want to get some more voltages, then you need to adjust inside of PSU.

other IC:
LM1085 -- 3A
LM1084 -- 5A

ATX Based Bench Power Supply to LM317.
http://www.wikihow.com/Add-Variable-Voltage-to-Your-ATX-Based-Bench-Power-Supply

Here is a variable power 0~330V.
http://www.oocities.org/tjacodesign/300vsup/300vsup.html