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NC transistor?

Discussion in 'Electronic Basics' started by Kevin Doney, Nov 9, 2003.

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  1. Kevin Doney

    Kevin Doney Guest

    I want to control a 3.2V 20mA normally closed circuit with a normally open
    circuit.When the NO circuit becomes closed I want to open the NC circuit. I
    want to do this by using the 3.2V power from the NC circuit. Is there such a
    thing as a NC transistor?
     
  2. Lord Garth

    Lord Garth Guest


    Look up 'depletion mode MOSFET'
     
  3. There are various ways to do this kind of thing. A JFET works this way,
    where it passes current when the gate is near the source in voltage. When
    the gate diverges from the source voltage (for an N channel, when it gets
    more negative, or for a P channel, when it gets more positive) the
    transistor will pinch off the current through it.

    If you hook up the base of an PNP transistor to the gnd side of the NO
    switch (through a 1k resistor), it'll pass current until the NO switch is
    closed. If the potential of the base then goes positive, it'll turn off the
    transistor.

    View with monospaced font:


    VCC
    +----------+
    | |
    | |
    | o |
    |=|> NO |
    | o |
    | |
    | ___ |<
    +-|___|--| PNP
    | 10k |\
    | |
    | |
    .-. .-.
    | | | |
    | |Load1 | | Load2
    '-' '-'
    | |
    | |
    +----+-----+
    |
    ===
    GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    When the pushbutton is open, Load2 will be powered. When the pushbutton is
    closed, Load1 will be powered, but Load2 will not be.

    Regards,
    Bob Monsen
     
  4. Kevin Doney

    Kevin Doney Guest

    Thank you. I used the PNP transistor and it works fine.
     
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