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how can I turn on ATX power supply without PC?

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Advanced Member level 4
May 17, 2002
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aatx power supply schematic


I want to turn on and Off a ATX power supply but without pc(standalone)

please give your solutions.


You also can find detailed explanation on No need to build schematic.I can't remember clearly but you should connect power good pin (green) to vcc.(I'm not sure please have reference)

Normaly the grounding of the inpulse line will bring on an atx power supply.One thing to remember is that you have to load the +5 volt rail and allso the +12-12 rails.

just short green wire to GND (black ones)

A tricky piece of information:

This type of power supplies needs "Minimum Load Current" to be drawn from the +5V & +12V concurrently in order to sope the o/p current range to it's full range. i.e., if you load the +5V only you will get only about 500-600 mA before the o/p voltage starts to drop down dramatically.

This is my own experience with this type of SMPS. I had to draw 2A of the +5V and 2A from the +12V to supply my 1.5A@5VDC uC based circuit.

Hope this helps.

First I recommend you read ATX spec, and then Just short the PIN PS_ON and GND of ATX connector.

Yes,You need a short between pin14 (PWR_ON,green) and pin15(GND,black). Most of ATXPSU have voltage feedback only from 5V output. If you apply a load only 12V out, the PSU switched off,because the overvoltage circuit detect a failure.In this case apply abot 1...2A dummy load to 5V out.(as busmaster wrote) I`ve made a 14V 15A accu charger from old AT supply (better construction as today...).

Hi Sebi,

tell me more about this accumulator charger - how can I obtain 14V from

Is it possible to increase the voltage from standart ATX power suply?

Yes, megamicro see this:**broken link removed** ,
In this circuit the output voltage depend from voltage divider on TL494 pin1. R20 and R21 go to GND. When You decrease R21 the output voltages increased. R25 and R26 feedback resistors from 5V and 12V outputs.(here is some drawing failure.)
If You want modify to accu-charger, apply feedback only from one output(12V) and remove the components for other outputs and overvoltage protection.

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