Every electronics workbench needs a power supply. Depending on your experience and type of projects, you might even need multiple power supplies. Converting a PC power supply to bench use is one option, but I needed something smaller with variable output voltage. A variable output of 0-15 vdc @ 1 amp and a built in voltmeter, to more more specific. So off to eBay I went looking for a project case, panel mount voltmeter and some other small parts. One of my eBay searches turned up a new tattoo power supply for $6. Well here was my case, digital voltmeter, switches and power cord for a fraction of the price of the individual parts. If I was lucky, some of the internal parts could also be used.

While waiting for this unit to arrive, I found two more tattoo power supplies for under $6. Neither was as nice as the first unit, but would be a good starting point for additional bench supplies. When the unit arrived I found the front jacks were 1/4 in. phone jacks. It would be simple to replace them with binding post banana jacks. Out comes four screws and off comes the cover.

The circuit board to the left is a switching power supply. It converts the incoming 110-220 vac to 20 vdc @ 2 amps. On some tattoo supplies this board is replaced with a transformer and a full wave bridge rectifier. The circuit board to the right is a standard variable voltage regulator which uses a LM317 regulator. As luck would have it, only a few mods would be needed for bench use.

The binding post banana jacks went in first. Removal of the phone jacks was simple, just unsolder them from the circuit board. The holes in the front panel were the perfect size for my new jacks. Next up was increasing the size of the output capacitor. Tattoo guns don’t require good filtering but having a good output filter capacitor is important when powering electronics. The factory unit was an off-brand capacitor rated at 1000uf @ 25vdc. For a replacement I used a Panasonic FM series capacitor rated at 2200uf @ 25vdc.

The cooling on the LM317 voltage regulator also needed upgrading. The factories choice of a heatsink was the painted steel case. There was plenty of room to add a heatsink to the back center of the case. Moving the LM317 required adding a few inches of wire to the leads.

That was simple and cheap! The cost of the bench power supply, including all parts, was under $10. The result is a professional looking bench power supply with an output of 1.25 – 15 vdc @ 1.5 amp. The LM317 features over current and over temperature shutdown. A fuse in the panel mount IEC C14 power jack provides additional protection and safety. Here are a couple more pics of the finished power supply.

More on this topic

3 Responses to “A Mini Benchtop Power Supply”