Power Supply build Part 1: requirements


Building a power supply is a rite of passage for electronics experimenters. I grew up in an age where all power supplies, even “wall warts,” had heavy iron transformers. In the last decade or two, better power transistors have become available, making possible switching power supplies, which are much lighter. (Think of your laptop power converter, or one of those tiny USB power adapters.)

So, there’s more than a bit of nostalgia in play here. I can build something better than what I’ve gazed at longingly during my school years. It’s also a good example of an end-to-end design process, and a time to reflect on how far along technology–and my life–have progressed.

Every project starts with requirements:

1) I want dual, independent supplies. I like to play around with op-amp circuits, many of which require separate positive and negative power lines.

2) A reasonable maximum current, but with adjustable current limiting and short-circuit protection.

3) Fine adjustment. I want to dial in exact voltages and currents, down to the hundredth of a volt or amp.

4) Digital display. Analog meters look cool, but I want the precision of digital.

5) Prominent earth ground connectors up front. When building radio circuits, you often need an earth ground connection handy. And many components are static-sensitive and require protective equipment, which includes a path to ground to dissipate any charges.

6) Repairability: My prior supply was a (single-ended) cheapo box from Fry’s. One day, it started spewing smoke every time I powered it on. I didn’t get very far in troubleshooting what went wrong. I want something made out of cleanly-separated components, which I’ve hand-picked. I want to be able to upgrade or repair anything, as I wish.

Just satisfying 1-5 would put things in the $4-to-$500 range. And the last requirement can only be met by building something yourself. Add to that the satisfaction of using a tool you designed and built with your own hands. The answer is clear. We’re going to build this thing.

Up next: component selection.

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