Computers & Mobile Technology

Phil Levchenko shot this tutorial showing how to turn an ATX power supply into a DPS.

Small tutorial on Computer ATX Power Supplies. How to use them, how to connect them in series, in parallel. What is 12V rails? Is it possible to connect 12V rails together? ATX connector wiring explained. What is difference between old computer power supplies and new ones? And finally how to make Lab Bench Power Supply from Computer ATX Power Supply.

24 thoughts on “Turn a Computer Power Supply Into a Desktop Power Supply

    1. I think it was just for aesthetics. Personally I like the heat shrink over mini zip ties any day. I have made similar but it looks like I’ve not quite got mine set up right so off to go get some resisters. It explains why mine is not so stable when I turn things off and so on. Excellent post/write up.

      1. I think so as well. While tying all of the 12 and 5v lines together is a good fool-proof way to get all of the current limiters in parallel you could probably trace the lines to eliminate some of those extra wires or even just jumper them on the board and tie it to a single larger guage wire as well. Whatever floats your boat really. Still very well done.

  1. I’ve done this but was trying to be cheap and not buy anything.  Instead
    of the 10 watt resistor I used an automotive turn signal bulb I had laying around. I just soldered directly to the bulb because the sockets are rather expensive plus way too bulky.  It works great!  That was with an older supply where I needed the load on the 5V rail.  Since the bulb was rated for 13.5 or so car voltage it doesn’t get too hot and will probably last far longer than it would in an actual turn signal.

  2. I’ve done this but was trying to be cheap and not buy anything.  Instead
    of the 10 watt resistor I used an automotive turn signal bulb I had laying around. I just soldered directly to the bulb because the sockets are rather expensive plus way too bulky.  It works great!  That was with an older supply where I needed the load on the 5V rail.  Since the bulb was rated for 13.5 or so car voltage it doesn’t get too hot and will probably last far longer than it would in an actual turn signal.

  3.  With a little research (Google “ATX power supply schematic”), you can tweak these supplies to produce either one output at higher current, or a variable output voltage.  By measuring the voltage across a series resistor, you can add current limiting. If it runs off a TL494 chip, the voltage on the feedback pin can be varied to change the regulated output voltage.  You’ll need to defeat the overvoltage protection circuit, though.

    I once got myself a bunch of three  350 watt AT power supplies, and discovered that they were all based on the same design. I modified one of them to put out 13.8 VDC at around 25A and used it to power a land mobile 50MHz transceiver converted to ham radio frequencies.  To purchase a new 13.8V 360W DC supply would have been over $500.

    If you want to learn about switching supplies, grab a few of these old supplies and try to identify the regulator chip used in them.  Then search for application circuits on the chip maker’s website. Odds are very good that the supply you have will be based on that circuit.  Identifying the voltage feedback pin is key…vary the voltage on that pin and the output voltage will change. 

    Be careful messing with these, there’s high voltage in the primary that can kill you.  Treat them with respect, but use the fact that these supplies are plentiful and almost free.  If you blow one up, chuck it in the bin and use what you learned to work on the next one!

  4. So where does the gray “power OK” wire go? i’m assuming on an l.e.d.? And my box already has a switch, that runs through a breaker and fuse. This isn’t going to change the project right? I don’t see it being an issue… really just curious as to the positioning of the “power ok” wire… (Can I just use this as the 5 volt connected to the l.e.d.? you have a red wire it appears…

  5. If I am right, it’s OK to make combinations connecting diferrent output in series. I mean -12 and 12 = 24v, 3.3 and 5 = 8.3v. It’s that possible?

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My interests include writing, electronics, RPGs, scifi, hackers & hackerspaces, 3D printing, building sets & toys. @johnbaichtal nerdage.net

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