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Using a transistor as a switch

  1. Jul 26, 2012 #1
    I have a battery operated digital timer circuit board that will control a small motor, via a control board.
    The timer runs on 3.6vdc (batteries). The timers Output Control Signal is 3.6vdc when on, and 0Vdc when off. The timer is replacing an old analogue timer.
    The old timer had normally open switch contacts.
    I think that I will need a transistor to act as a switch, can anyone recommend a transistor and resistor (if needed) that would be suitable for this scenario?
  2. jcsd
  3. Jul 26, 2012 #2


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    What voltage and current levels do you need to switch Christo? You could probably use either a BJT or a low threshold MOSFET.

    Low threshold mofets are designed to allow switching with gate voltages as low as 2.5 volts (some probably even lower). You may get a slightly better approximation to a short circuit with a mosfet compared with a BJT.
  4. Jul 26, 2012 #3
    Thanks for the reply uart

    I will run some tests to check out the current and volts, but to give you an idea of a similar motor see below:

    6 Vdc
    70mA no load
    640mA full load
    700mA stall

    Last edited: Jul 26, 2012
  5. Jul 26, 2012 #4


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    Science Advisor

    A small low threshold mosfet would be ideal. You can usually drive the gate directly directly from the 3.6 volt logic output.
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