Posts Tagged ‘tech’

Power Supply Design

July 26, 2010 5 comments

I’m starting out with a highly useful project.

Realising that i need a decent power supply for my projects, and a place to work from, I looked at getting myself a bench top power supply, but at £100+ for a decent one, I looked into building one and came across this instructable. It looks like i can build one for less than the cost of buying and it should give me more output options and more current. Since the whole point of this adventure is to start building stuff from scratch too, it makes sense to make it myself.

The principle looks fairly simple and the only circuits required seem quite basic so i jumped in and started ordering parts.

While i was waiting for parts, i set about designing my new power supply in google sketchup (free):

(download .skp file)

The power supply is based on an old pc ATX power supply. This is great because they are cheap, efficient and provide a huge amount of current on demand. I didn’t have any spare power supplies lying around so i asked a few friends and managed to get a nice 550w supply for free. This has a huge 12cm fan on top which will be useful for cooling my electronics as well as the supply itself.

The supply has a bundle of wires coming from it. All wires of the same colour provide the same function and so can be bundled together.
the voltages provided are:
-12v: blue wire
3.3v: orange wire
5v: red wire
12v yellow wire
as usual the black wires are ground
There are a number of other wires coming from the supply and these have special functions that i’ll explain later. If you’re curious you can look at the wikipedia page

in addition to these outputs I’m adding a variable output by using a variable low drop out, linear voltage regulator on the 12v line. This should give me from 1.4v to 11.6v with a couple of amps.

ATX power supplies have had a number of revisions and some older ones include a -5v output on a white wire. Unfortunately this one doesn’t but I don’t think I’ll miss it much.

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