0-30V Mini Desktop Power Supply

0-30V Mini Workbench Power Supply

After years of using this ugly and bulky benchtop power supply, I decided it was time to build something better, smaller, and more aesthetically pleasing. It started with a variable power supply based on an LM338 5A voltage regulator and an external power adapter. The LM338 datasheet has several very useful application notes and circuits. I chose one illustrating variable output and including a protection diode. The diode is included to protect the regulator from damage in the event of an accidental short circuit to ground at the input. This is an obvious possibility if it's connected to the power supply using a jumper. Furthermore, the benchtop power supply output could short-circuit if other equipment fails. Without the diode, if this happens, the capacitors would discharge through the regulator. Since current spikes can reach many amperes, the regulator could fail. The diode directs the current around the regulator and into ground, thus protecting it from damage. With sufficient input, the LM338 can make an excellent variable power supply. This small power supply is user-friendly and perfectly suited to my cluttered benchtop.