How to Add Variable Voltage to Your ATX Based Bench Power Supply

Last Updated: February 6, 2023

If you've built a bench power supply using an old ATX power supply, you may feel limited by the choice of voltages. We'll show you how to expand your options by building an add-on variable voltage module for your ATX-based bench power supply.

Steps

1
Gather the materials required and construct the circuit from the circuit diagram. It would be a good idea to get the datasheet for the regulator from the manufacturers website.
2
Get some banana leads and connect the +12V and -12V outputs from your modded ATX supply and connect it to the input of your variable module. Use a multimeter to measure the output voltage.

Advertisement
3
Once you have built the circuit test it carefully and measure the output voltage. You should be able to vary the voltage from about 1.5V up to 22V by turning the variable resistor. If you are using the LM317 the output current will be restricted to 1.5A, if using the LM338K it should be slightly higher check the datasheet for exact information.

Warnings

If you've already built an ATX Power Supply based bench/lab supply, you've already run the risks - this project is less dangerous. Soldering irons can burn you, hand tools can cut you; don't drink and hack.

⧼thumbs_response⧽
Helpful 1 Not Helpful 0
Since any part on your circuit isn't really 0v(gnd) when you put it into your ATX case don't let any part touch anything, even the case.

⧼thumbs_response⧽
Helpful 3 Not Helpful 4
Use common sense. If you find the regulator gets hot use a heatsink.

⧼thumbs_response⧽
Helpful 0 Not Helpful 0

Things You'll Need

You will need the following materials:
1x LM317 or LM338K Voltage regulator (With heatsink and heatsink paste)
1x 100nF Capacitors (ceramic or tantalum)
1x 1uF Capacitors Electrolytic
1X 1N4001 or 1N4002 Power Diode
1X 120 Ohm resistor
1x 5k Ohm variable resistor
Optional
- Some Veroboard or a matrix board and some suitably thick wire for connecting the circuit.
- A small enclosure about the size of a wall wart to put the circuit in.
Indispensable
- An ATX power Supply already modded to provide +12V, -12V, +5V and -5V