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Simple power circuit question

Discussion in 'General Electronics Discussion' started by jj2012, Apr 2, 2013.

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  1. jj2012


    Apr 2, 2013
    Hello, I have a simple question (I am not an expert on electronics and electronics components).

    I have a micro-switch that is acting as a power supply on button for a PC motherboard, however, for the board to function correctly, a seperate 12V DC supply must be plugged in first (as it provides power for hard drives and so on, that the mainboard uses)

    1) Is there a way that I can have the micro-switch so that it cannot complete the "power on" circuit if the 12v supply is not connected (pressing it would just do nothing, forcing the other power connector to be plugged in first)

    2) Is there a way to have power to the mainboard cut off immediately if the 12v power supply goes off for any reason (for example, accidentally pulling out the DC plug)

    Any help would be appreciated, I can wire up a basic circuit, but I don`t have any idea how to solve this particular problem.

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    What does this switch do? Why do you have 2 different power supplies?

    A simple (although wasteful) way of doing this is to have the 12V rail drive a relay that is in series with the microswitch.

    There are probably simpler and more elegant ways, but we'd need to know more.
  3. jj2012


    Apr 2, 2013
    Thanks for the reply Steve. The switch is a temporary push to make style switch, that is part of the standard set of PC switches and lights (two LEDS, one power, one reset switch). All it does is temporarily make a circuit that informs the motherboard the power button on the front of the PC has been pressed once.

    There are two power supplies as the motherboard takes 19v but there is another board in the system that takes a 12v supply, and I did not want to overload the 12v rail from the motherboard. Both of these supplies are DC adapters.

    I was wondering, would this circuit be possible with a simple transister? I tried it in a online testing applet, and it seemed to prevent the power signal being sent if there was no power going on the other circuit. Would there be a problem because of the two different voltages?
  4. jj2012


    Apr 2, 2013
    just did some investigating, looks like a relay is exactly what I need.
  5. gregfox


    Mar 25, 2013

    Use a SSR?
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