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555 timer circuit help

Discussion in 'General Electronics Discussion' started by stevenc_hmfc, Aug 25, 2011.

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  1. stevenc_hmfc


    Aug 25, 2011
    Hi, iv built this circuit but the relay is constantly closed. I want it to be closed for a set amount of time. Any ideas if somethings wrong? Thanks

  2. JoeyAVR


    Aug 25, 2011
    Are you sure that the relay isn't wired wrong and staying permanently open?

    With the load on the low side of the mosfet the gate shouldn't be getting enough volts to turn on in the first place.

    Put the relay between the mosfet and 12V instead.

    There's no smoothing capacitor on the supply rail, which won't help either. use at about 100uF, close to the 555,

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