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The collector is a high impedance when compared to the emitter.

  1. Sep 14, 2010 #1
    Good Morning

    can anyone help explain what this statement really means, when refering to a npn transistor in common mode, as an amplifier.

    "The collector is a high impedance when compared to the emitter"

    what's the pratical implication of this statement


  2. jcsd
  3. Sep 14, 2010 #2
    it means that collelctor ckt is reverse biased (during active state of transistor)....so it is having higer resistance in this situation.

    emitter is forward biased (during active situation).so it is having lower resistance....
  4. Sep 14, 2010 #3


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    Science Advisor

    In an emitter follower, the output impedance is very low. It can be around 5 ohms or less.
    This means that you can put a load of this impedance on it and the output voltage will drop to half.
    In practice, this means that the output voltage of an emitter follower is almost the same regardless of normal load variations.

    In a common emitter amplifier, the output impedance is almost equal to the size of the collector resistor and this may be something like 1000 ohms to 10000 ohms. So it is a lot larger than the emitter output impedance.
    It is actually equal to the collector resistor in parallel with the output impedance of the transistor.
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