Electronics > Projects, Designs, and Technical Stuff

Show your homemade power supply

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TheMG:
My first foray into building a bench power supply (about 10 years ago). Essentially two completely independent linear regulated power supplies in a single enclosure, each capable of 30V up to 3A.

The case, transformers, heatsink, pass transistors, bridge rectifiers, and a few other components are salvaged from e-waste.

In the first picture, modifying the toroidal transformers. I added a couple of taps to the main secondary winding, these are selected by relays to reduce power dissipation in the pass transistor at lower voltage settings or when the power supply is in current limit. I also wound an additional auxiliary winding on top to provide power for the control circuits.

Pic 2: front panel assembly.

Pic 3: once the front panel and transformers were assembled as well as the pass transistors on heatsink, it was time to prototype and test the circuit on breadboard

Pic 4: etching PCBs using the toner transfer method, and extremely caustic hydrochloric acid / hydrogen peroxide mixture as etchant (rather dangerous compared to ferric chloride, but all the necessary chemicals can be obtained at any hardware store, and the only option for me obtaining ferric chloride is to order it online)

Pic 5: assembled PCB. the connectors are of course yet another salvaged part, and they are a much nicer alternative to soldering the wires direct to PCB, in case further modifications or repairs of PCB are ever necessary, it can be easily removed

Pic 6: PCBs mounted above transformers on custom made aluminum brackets, time to finalize the wiring!

Pic 7: with the wiring all cleaned up and rear panel installed

Pic 8: done (except for labelling the controls). big knobs are voltage settings (10-turn pots), small knobs are current limit setting (single turn)

It's not going to win any awards as far as how clean the output is (does have a few mV 120Hz ripple, probably due to using the output of LM7812 as the voltage reference rather than an actual proper voltage reference), but it's good enough for my needs and I still use it fairly regularly even to this day. I could make some improvements to it but just haven't bothered.

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