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Power Supply Design

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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  1. March 27, 2012 at 5:51 am

    Simply wish to say your article is as astonishing. The clearness for your post is simply spectacular and i could think you’re a professional on this subject. Fine with your permission allow me to take hold of your feed to stay updated with drawing close post. Thank you one million and please keep up the rewarding work. Drop by my page . thanks.!

  2. BrAtKo
    March 18, 2013 at 9:29 pm

    Thank you for publishing SKP file, I have tried SketchUp and it is damn easy. You helped me with your skp Ive used the binding posts and LCD in my project.

  3. October 24, 2013 at 5:34 pm

    I am working on setting up my electronics’ lab in my home office and am looking at getting / making a bench top power supply. I found a programmable one that I like but I would want some changes. I would like for it to have 2 separate adjustable voltage / amperage outputs along with 2.5V, 3.3V, 5V, +12V and -12 V from 0-3 Amps. For the power supply I think that 30 volts at 3 amps would do anything that I would want.
    If you could ever help me out with this idea I would be able to do the sheet metal fabrication for you with some sketchs of the heatsinks, digital meters, hole patterns and stuff… you would not have to draw everything, I could fill in the blanks with my CAD system.
    Here is another nice power supply that is programmable that you may be able to use the software from to operate the design you may come up with if you are up to the challange. This project is a bit over my head right now or I would not be asking for your assistance if you ever have the time to mess with it… if you are like me you probably have enough projects to last a life time.

    Thanks for your time and have a great day!
    Rick Linnabary Jr.

  4. CristiMC
    November 20, 2014 at 12:29 pm

    Your article was very helpful for me. Can you re-publish the SKP file (or send it by email) ?
    Thank you !

  5. Lee Frost
    January 3, 2016 at 12:17 am

    hi, love your psu conversion, just a query – in your parts list you have one rotary switch and two dpdt swiches, but your schematic shows 2 rotary swiches and one dpdt switch, am i missing something, the only other thing is both 4 position rotaries only seem to use 2 positions each..?

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