Connect with us

Push button start-stop computer psu without motherboard

Discussion in 'Power Electronics' started by Bobsone, Jan 3, 2016.

Scroll to continue with content
  1. Bobsone


    Jan 3, 2016
    First the disclaimer, I am a novice, I have a little experience with building circuits so I can claim enough knowledge to get myself into trouble...

    I thought I could use a tiny ITX case with an onboard 60w power supply to hold and power a phono preamp and a headphone preamp (both 12v). I still have to check the wattages but I am still at the idea stage and I don’t think they will exceed the PSUs 12v rail(s).

    My problem-question;
    How can I use the push on-push off button on the front of the case to start the internals. I know that starting a PSU without a motherboard requires the grounding of the green (5v) wire in the 20/24 connecter, but how to do this with the front panel push button and no motherboard.

    My online searches have lead me to push-on push-off latching circuits which would be great... Unfortunately I think it won’t work in this instance because I am wanting to ground the positive supply that is also powering the circuit.
    E.g. or a transistor based version
    I then thought about using a latching circuit (powered from the input side of the PSU) to provide power to a relay which would ground the 5v start circuit. However, I suspect I would then need to have some other circuit working in conjunction with the relay to control any “bounce” associated with the relay operation.

    My third idea was to permenately ground the 5v start wire and use a latching circuit to switch the PSUs input. But this isn’t a 5v milli amp circuit anymore..... and what will the PSU start up supply look like?
    E.g. something like this; Driving capacitive loads, Figure4,
    I don’t currently have access to the case/power supply so I can’t be more specific or do any tests like will it start and continue running without a motherboard, does the power supply have feedback circuits. I know some PSUs need a constant load to prevent an auto shut down and have seen people use a 10w 10 ohm resistor across a 5v rail to solve the problem.

    Is my plan viable, possible, is there a better solution (I can’t be the first to try something like this). I would appreciate your advice, tips, cautions etc.

  2. Martaine2005


    May 12, 2015
    Hi Bobsone,
    Does the psu have a purple wire?
    That would have powered a constant 5v USB port as long as the main plug is plugged in.
    So the latching circuit would work with that.
    Failing that, most people switch the green wire. But obviously that would need to be an on/off switch.
    You may be able to find or alter a switch to go behind the casing switch.

    CDRIVE likes this.
  3. AnalogKid


    Jun 10, 2015
    One option is a toggle switch. Flip up = on, flip down = off. If you really want a push-on/push-off button, you need an alternate action pushbutton switch. Either way, grounding the control wire (pin 16, often a green wire) enables the supply. Switch bounce is handled inside the supply. Note, some ATX supplies require as much as a 10% load on the +5 V output before the rest of the outputs regulate reliably. Also, you are using a very noisy supply to power an audio circuit that is very susceptible to noise.

  4. Bobsone


    Jan 3, 2016

    Oh beeep (bother), power supply noise;
    Here I was thinking I had a good plan, alas I didn’t consider PSU ‘noise’.....

    Thanks Martin and AK for the responses.

    I collected the case yesterday and for reference I have found it online here
    The good news is that it does have a purple 5v wire and I have found a circuit that should do what I want.
    I would need to leave out the relay/diode, connect the switching 5v (green wire) to T1s collector and use the constant 5v (purple) to power the circuit.

    As for maintaining some load on the supply I was thinking (hoping) that because this is only a 60w supply, if it does need some extra load then it won’t be a huge amount.

    But noise...
    Oh dear.... If this is a problem, is there a downstream solution or is it better to scrap the PSU idea in favour of a different 12v and perhaps a 5v power source?

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day