The ATX power supply for PC base server requires the front panel switch to trigger in order to make it funtioning. However for nonUPS server, when power failed and power on again, we need to press the front panel switch to turn on the power supply. I have seen the method to use enable signals of the ATX power supply by shorting the GREEN wire to the BLACK wire. However some of the ATX supply may not provide such enable pins. Here is another approach, using the 555 IC to provide trigger signal when power ON automatically. The method is quite safe and reliable. I have tested it with Ubuntu server made with the Compaq PC.
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The circuit is a monostable built with the popular 555 timer IC. This circuit provides a pulse trigger period approx. 2s.The output is open collector type, so we can tie the collector pin to the power trigger switch safely and easily. The collector will pull logic at the POWER SWITCH signal to LOW approx. 2s.
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As shown above picture, we can build it with universal PCB. Q1 can be any small signal NPN transistor. Testing is done by turn off the main AC plug and then turn the power on. After approx. 2s the server will be booting.
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