+ 12volt and -12volts from pc psu. Can I get 24 volts?

I have an unused pc atx psu. I want to make a bench power supply. The usual ebay breakouts give 3v 5v and +12v and -12v. Can I use an LM317 and make a variable output up to 24v? Any advice gratefully received.

• you can, but the total current would be limited by the -12 V supply current, which is very low ... you would also not be able to use the resulting 24 V output in the same circuit as the 5 V output Feb 28, 2021 at 21:07
• If you look at the manual for your power supply, there is usually a list of the power supply's rails and if the supply is modular, often a list of which ports connect to which rail so you can balance loads better between the rails. You might be better off running an isolated 12-24V boost converter off of a decently powerful 12V rail.
– K H
Feb 28, 2021 at 22:12
• I'm a noob and tried to help a friend with his home-brew 3D printer. I suggested we re-purpose an ATX and while we learned a lot there was a heck of a lot of workarounds and he ended up buying a non-ATX. In my experience you'd be getting yourself a bunch of unexpected problems. If you can afford the \$20 buy something designed for your project's needs. Mar 1, 2021 at 19:24

Can I use an LM317 and make a variable output up to 24v?

No. The LM317 has a voltage drop of ~2V, so the maximum you will get is ~22 V.

A better solution would be to boost the +12 V to +26 V using eg. an XL6009 based module, then regulate down to the voltage you want with the LM317.

To reduce power dissipation in the LM317 at lower output voltages you could turn the booster output voltage down, eg. to 14 V when the LM317 is regulating down to 12 V, or 12 V (minimum possible booster output) when regulating down to 10 V and lower.

• I'm experimenting with TI MSP430 microcontrollers for which the power requirements are modest. But there is often a need to do something real such as automate my house climate control so higher power is required. It's interesting that you can play around with electronics at a signal level ie microcontrollers and get some useful results without really understanding the fundamental electrical properties. Sometimes you just want to experiment with a coil of wire and see what happens so this is where the higher voltage comes in. Mar 6, 2021 at 19:17