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Homework Help: NPN Transistor

  1. Apr 23, 2008 #1
    Is the voltage drop across the emitter in an NPN transistor equal to 0?
    What is the purpose of RE (found immediately after the emitter?)
    Last edited: Apr 23, 2008
  2. jcsd
  3. Apr 23, 2008 #2
    I think you're picturing the collector-emitter junction, and one or more resistors in the collector and/or emitter paths, spanning the range between the positive and negative terminals of a power supply. The transistor needs to accomodate two opposite states. If the base current goes high, the transistor conducts, the collector-emitter junction doesn't have much voltage across it, and then the resistors bear most of the power supply voltage. If the base current goes low, the collector-emitter junction stops conducting and takes up a lot more of the power supply voltage, and then the resistors won't don't get the voltage. You're expecting to go back and forth between the situation big X + small Y = constant and the situation small X + big Y= constant.
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