D.I.Y Power Supply.

This page contains diagrams for building a simple 5V/12V power supply of your own.

Basic 5V/12V dual output power supply. Not very fancy, but it's still a major improvement over batteries.

Introduction

I've recently found I need a bunch of equipment that I previously did not have. So I'm posting schematics here. If anybody wants any premade versions of these, or if you find these diagrams useful, just drop me a line (address on front page) and let me know.

Benchtop Power Supply

This is just a basic 5V/12V dual-voltage linear regulated power supply. It can deliver about 1A continuous current from either output (in theory, anyway). The transformer is a 13V center-tapped model. Diodes D4 and D5 steer the current to C3 and C3, where it is regulated by U3 and U4.

Diodes D2 and D3 provide power-off protection for U3 and U4. Capacitors C4 and C5 act to debounce the final output.

Component values are almost irrelevant. The diodes should be standard rectifier types (1N4001 work well). C2 and C3 should be large electrolytics rated for 10V or higher. C4 and C5 are ceramic discs. The only critical value in the circuit is R1, which limits the current in the LED. This should be somewhere between 220 and 470 Ohms, depending on the color of the LED and the brightness you desire.

Construction

Tools. Lots of tools. From left to right: nibbler tool, rubber mallet, cordless drill, safety goggles, Dremel rotary tool, power supply base, various electronic components, metal-cutting drillbits, 24lb anvil, bolt cutters.

While finding components to build my power supply, I found that I didn't have any metal project enclosures left. So I went looking around for ideas.

Inspiration struck in a Canadian Tire store (hardware store, for anyone who's not Canadian), when I found auto body metal (apparently 20 mil mild steel, or so someone told me later). So I bought a sheet and took it home.

Having never worked with this material before, I tried a few things. I took out a pair of aviation snips and tried cutting it. It worked, but it was tough to cut. Eventually I cut out the outline of the base (a simple rectangle shape).

I then tried to bend it. Well, I found out quickly enough that steel sheet is *NOT* fun to bend by hand (while it's bendable, if you really try, it won't give you a nice crease). Since I can't afford a sheet-metal brake, I decided to try this the old-fashioned way. A year earlier, while experimenting with circuit resist ink thermal transfer, I had picked up a 24-lb anvil. Realizing that, historically, metal wasn't always bent with a brake, I looked over at my rubber mallet.

One good solid migraine later, I had bent the metal into the shape I wanted, and was even starting to get the hang of shaping steel with a mallet. I used a mallet, instead of a steel hammer, because while I wanted to shape the metal, I didn't want to distort/flatten it. The extra give of the rubber (so I guessed) would prevent such things from happening. It seemed to work well enough in practice.

The base of the power supply. Small round holes were drilled. Large round holes were drilled and then enlarged with a reamer. Square holes were drilled, then enlarged/squared with a nibbler.

Once I had the basic shape, I made some estimations of where everything would fit. I layed out where all the holes should go, and then drilled them. My drill is only 3/8", so some holes were beyond its capability. In these cases, I took a simple tapered hand-reamer and enlarged them.

The square hole for the switch and the shaped hole for the computer power connector were started with a drill, then shaped with a nibbler tool. Much to my surprise, the nibbler cut through the steel without much trouble!

Now, after all this cutting and drilling, the steel was starting to feel pretty sharp. I attached a grinder wheel via a flex shaft to my Dremel rotary tool. I ground the edges down, and deburred the holes/slots.

That left the painting. While I probably could have gotten by without painting it, corrosion would have been a problem (the humidity where I live is extreme). Besides, a nice paint job makes anything look better. I am a loyal Tremclad fan, since a really positive experience I had with it during my time experimenting with printed circuit boards. However, all I had was machine blue. While that may be appropriate for screen-printing equipment, it doesn't look right on electronics. So I went to the hardware store and bought a can of "Recreational White" (off-white), and one of "Low-Gloss Black".

The power supply, with basic layout added. On the front panel, from left to right: power LED, ground plug, +12V plug, +5V plug, power switch.

A rear view of the power supply. On the rear panel, from left to right: computer power cord socket, fuse holder.

After letting the paint dry, I mounted the components to test the fit. The perfboard is a standard prototyping board, which I cut a notch out of (using the nibbler tool) to make room for the transformer. As is shown, the power supply is designed to use a standard computer power cord (I found a connector in my junk bin).

Power supply, with electronics installed. This is a view from after testing, right before the lid was attached.

After that, it was a simple matter of populating the circuit board, wiring the 110V routes, and adding finishing touches like connector blocks, wire ties, and pin headers.

It should be noted that the schematic shown above is *NOT* the original design used in this power supply. The original design didn't work, thanks to a short circuit caused by a couple of extra diodes. I'm lucky I used a fuse. Once I pulled those diodes, everything worked flawlessly.

I built a lid using the same techniques as the base. Now that I had some practice, this didn't take a lot of time. The most time-consuming aspect was waiting for the paint to dry.

The final product.

In the end, I was left with a cute little bench power supply, and a new skill. It was well worth it.

All material on these pages is Copyright (c) Jennifer E. Elaan.