relay based power on after failure on pc

Oct 18, 2007 3 Replies

my bios is not doing it..


i think that the trigger has to be the 5 volt from my ATX power supply that "says" (magenta color cable ) to the motherboard that is ready to turn on (and supplies the modem or and the network card if they are waiting a signal to wake up on lan / or wake up on modem)



but here's the problem....



we have to make a circuit that..



.. if there's 5 volt at the input ( and not below that ) then after milliseconds.. the relay ( which is parallel to the on / off switch)



goes to the other position and turns on the computer..



but it can't stay at this position because it is like we hold still the on/off button and you know if you hold it for 5 seconds it turns of the computer.. so after let's say half of a second the relay must go to it's first position and stays there until the circuit loses for a long time eg 10 seconds ( avoid here micro-time-loss of network supply eg during a thunder strike) and then .. having 5 volt input starts triggering / cycling again....


for the 5 volt reference we 've got to have a 5V zener, for delay a capasitor charging or an 555.. a classic relay.. but how the circuit is gonna be?



... here i need your help.. thanks for your time...


well alternatively .. we can trigger it , simple, with the 220 V from the public network, but we must delay it so the ATX is ready to give full power to all the pc parts....



This will give you a ~ 1 second delayed negative at the output after the 220 is restored:

------ | 12V +|-------+----+---[10K]----------+---> output 220===| | | | | | | | [3.3K] | | | | | 6.8V /c | -|--+ [1K] +---[Zd]---[1K]---| NPN ------ | | | \\e | | [100uF] | | | | | +----+----+------------------+

After the power is restored the 100 uF will charge through the 10K. When the charge reaches about 7.4 V (in roughly one time constant [3.3K*100uF seconds]) the transistor will conduct and the output will go negative.

You can couple that to the trigger of a 555 monostable through a capacitor, and have the 555 operate your relay.

Ed

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