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Transistor question

Discussion in 'Hobby Electronics' started by DAC, Feb 16, 2006.

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  1. DAC

    DAC Guest

    I need to make a circuit and only have PNP transistors available at the smd
    size I am working with.
    I have 12V power and a input signal that is either 5V or 0V. I want to use
    the transister to make an output that is 12V when the input is 5V and 0V
    when 0V (or 12V when 0V and 0V when 5V is acceptable). How do I bias it to
    do this? I put resistor at base to 5V and resistor at collector to gnd, and
    emitter to 12V. But base is at 12V still. How do I calculate the resistor
    size values?? Output current not important (<1mA).
  2. Thats actually quite difficult - at least 2 transistors and 3 resistors.
    Are you *absolutely* sure you cant source an NPN transistor ? Even in
    a bigger size, would still be smaller overall than doing it with PNP only.


    Adrian Jansen adrianjansen at internode dot on dot net
    Design Engineer J & K Micro Systems
    Microcomputer solutions for industrial control
    Note reply address is invalid, convert address above to machine form.
  3. DAC

    DAC Guest

    The device ended up to accept 12V for logic high and about upto 9V for
    logic low. So I was able to use 1 transistor as a zener to swing the 12V
    with 5V no enough for the zener and full 12V enough.
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