Question About Computer ATX PSU

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Question About Computer ATX PSU

Post by fine-tune » Sun May 26, 2019 9:05 pm

In this article (and many others) there is a wire color chart for ATX power supplies: ... -Supplies/

I want to add a switch that will temporarily disable the automatic power-off
feature provided on most mobos (motherboards). Just to be clear, the operating
system shuts down and almost immediately after the PSU powers down. That's
the auto power-off feature.

I've built many desktops, but I never had a reason to change how the PSU operates.
I don't want to make a mistake and damage the mobo or PSU.

Here is a quote from the wire color chart:

"Connecting this wire to the black (ground) wire will pull the green wire's +5v signal
low, signaling the PSU to turn on. If you want an on/off switch, it should be this

I assume there is a control pin on the mobo that is normally low. This would keep
the green wire at ground and the PSU powered up. After operating system shutdown
the control pin flips high, powering down the PSU.

The question is, how to implement manual control of auto power-off. Something
very simple like adding an inline SPST switch to the green wire? I can't afford to
guess with a very expensive desktop. How should it be done?

(After googling about this topic I found some really uninformed suggestions, like
disabling Power Management ACPI in the BIOS. Not a good idea!)

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Re: Question About Computer ATX PSU

Post by dyarker » Mon May 27, 2019 4:30 am

In Windows under "Settings" then "Power and Sleep" change Time to Sleep to "never".

Some types of power supply can not regulate the logic supply (often +5V)((or 3.3V on newer)) when the current goes below a minimum. If forced to stay on, the voltage climbs till the mobo is fried.

I've also heard of software that simulates mouse movements, that prevents Windows from shutting down or sleeping.

Dale Y

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Re: Question About Computer ATX PSU

Post by Janitor Tzap » Mon May 27, 2019 8:23 am

Not sure what it is your asking? :?

If I understand right.....
You want the computer Motherboard too be shut down, but not the ATX-PSU.

I can see several problems with this.
With the Power Supply constantly on, it will be sending power to drives, Fans, Video Cards,
and anything else on the +12V,-12V,+5V,-5V,+3.3V lines.
This would possibly fry the Mobo, the drives, and damage cards that are in the computer.

What do you need too power, that you want to use the ATX-PSU?

Signed: Janitor Tzap

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Re: Question About Computer ATX PSU

Post by haklesup » Tue May 28, 2019 12:57 pm

For the most part "Auto Power off" is controlled either by the OS or by BIOS, all you can do in hardware is disable the ability of the MB to turn off the PSU so you can keep something else alive that you can't keep powered with the low current 5V that normally stays on all the time. Check your BOIS settings, you might be able to disable that without wiring changes. Aside from BIOS, tieing the control line to the active state seems reasonable. I think it can shut down and still be powered

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