How to Make an Adjustable Bench Power Supply From an Old PC PSU
A practical maker-style guide for converting a spare ATX computer power supply into a useful electronics bench supply.
An old ATX power supply is too useful to leave in a drawer. It already gives a strong 12 V rail, and with a small LM317 regulator board it can also become an adjustable supply for testing circuits on the bench.
Supplies
- Old PC/ATX power supply unit
- LM317 voltage regulator with heat sink
- 10 k ohm resistor, 470 ohm resistor, and 50 k variable resistor
- Mini voltmeter, switch, LED, DC connector, and output jack
- Vero board, soldering tools, drill, cutter, and insulating heat shrink
Step 1: Prepare the power supply
Open the PSU and identify the wires you actually need. The green wire is the enable line, black is ground, yellow provides 12 V, and orange can be used for the indicator LED. Trim unused wires so the final build is easier to service.
Step 2: Cut the enclosure
Mark the panel openings for the switch, voltmeter, output connector, and adjustment knob. Cut slowly and test-fit each part before locking the layout in place.
Step 3: Wire the switch and indicator
Use the switch to connect the green enable wire to ground. Add the LED with its current-limiting resistor so the front panel clearly shows when the supply is on.
Step 4: Build the adjustable regulator
Assemble the LM317 circuit on Vero board and feed it from the 12 V rail. Keep the heat sink clear of loose wiring and check polarity before powering anything.
Step 5: Assemble and test
Mount the fixed 12 V output and the adjustable output, close the enclosure, then bring the supply up with no load first. Turn the knob and confirm the voltmeter tracks the expected output range.
Safety note: ATX power supplies contain mains voltage and large capacitors. Work unplugged, avoid the primary side, and only continue if you are comfortable around power electronics.
Original project reference: DiYmon on Instructables.