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Using Transistor as Momentary Switch

Discussion in 'General Electronics Discussion' started by sall, May 16, 2011.

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  1. sall


    Jan 29, 2010
    I am trying to figure out how to use a transistor to operate as a momentary switch. Right now I am using a relay, a cap and a resistor. I would just like to be able to make the circuit a bit smaller than using a relay.

    TIA! :D
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, so you need to explain more.

    What will cause this "switch " to close?

    Do you want it to stay closed for a brief period then open again?

    What is this period?

    What is the load that you are controlling?
  3. sall


    Jan 29, 2010
    Yes, I apologize for the lack of information and hasty post. I have a relay setup so that it receives signal from 12V switched wiring in my vehicle and in turn acts as a momentary switch to power on my laptop any time the ignition is in accessories/run.


    I would like to do something similar with a transistor if possible to reduce the size of the circuit, but am unsure how to accomplish. I am planning on combining this along with other small circuits on one board for a carpc project.

    Attached Files:

    Last edited: May 16, 2011
  4. davenn

    davenn Moderator

    Sep 5, 2009
    by the time you have a transistor or 2 and associated components on a cct board and then mount that board in an insulated case its probably going to end up being bigger in size than the relay system you are currently using.

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