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ATX power supply on/off

Discussion in 'Electronic Repair' started by ee_design, Aug 6, 2006.

  1. ee_design

    ee_design Guest

    Can any one tell me how to effect a simple on/off control of a standard
    ATX type power supply to use it on bench or for other projects? How
    does motherboard control this function?
  2. Ralph Mowery

    Ralph Mowery Guest

    From the url below:

    While we're at it, you can power up an ATX power supply by shorting the
    green wire with any black ground wire. As you know, the ATX power supply
    will not turn on normally without a motherboard connected to it. There are
    times when you may want to test an ATX power supply or use the voltage from
    one but don't really want to hook up a motherboard. There's only one green
    wire and there are plenty of ground wires so it's easy to do. To use a bent
    paper clip and insert one end in the green wire connector and bend it around
    and put it into a black wire connector.

    Also you usually need a load on the output of the supply before it will
    start or stay on .
  3. It's usually a 'soft' logic switch. A momentary contact closure
    toggles a flip-flop in the supply which turns it on. A continuous
    closure of more than ten or so seconds usually turns it off.

    With that said: Using a PC supply for any type of serious bench
    work is a poor idea, IMO. They are often very (electrically) noisy, in
    terms of RF emissions, their outputs are rarely variable, and most of
    them need a minimum load on the +5V line to even regulate properly.

    There are plenty of very decent and affordable 'lab' type variable
    power supplies that show up at ham radio swap meets and electronic
    surplus places, to say nothing of Greed-bay. If you're serious about
    clean experiment power for your bench, or something noise-critical like
    servicing radio equipment, you should seriously consider investing in

    Happy hunting.
  4. Franc Zabkar

    Franc Zabkar Guest

    The logic is on the motherboard. The PS_ON signal is 'hard', ie there
    is no flip-flop in the PSU.

    - Franc Zabkar
  5. zack

    zack Guest

    for load you could use a light bulb 12v or a resistor
    accross ground and 5vline 50-100ohm.
    and a led on the power good se if it lights.
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