colector voltage in Dc analisis

Discussion in 'Homework Help' started by mosfat, Dec 8, 2013.

  1. mosfat

    Thread Starter New Member

    Dec 8, 2013
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    0
    i need to find the Vout voltage.
    i know drain current of M1 is 5mA

    i need to find the collector voltage in Q1
    how to do that?

    thanks
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,720
    4,788
    You need to show YOUR best effort to work YOUR homework problem. That gives us a starting point for discussion as it allows us to see what you are grasping and what you are overlooking.
     
  3. mosfat

    Thread Starter New Member

    Dec 8, 2013
    4
    0
    its like a chane
    my goal is to find Vout

    my work:
    it comes dows to finding the voltage on the collector of Q1
    the voltage on the base of Q1 is 4
    the voltage on the emiter is zero because its DC analises and the small signal is zero.
    the problem is ,if emitter voltage and its in the active state
    VB-VE=0.7
    VE=4 (the voltage sorse bellow)
    so VE cant be zero althogh its active state
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,720
    4,788
    Well, you seem to be struggling with the right things -- or at least realizing that you are struggling with the things where you are not going about it right.

    Yes, the base of Q1 is Vb=4V.

    But if the emitter is 0V, then you have a transistor with a 4V base-emitter voltage. At the very least this would have to be in hard saturation, if not well into the smoke-emitting region of operation.

    Yes, if Q1 is in the active state, the Vb-Ve=0.7V (or close enough for our needs), but then on what basis do you say that Ve=4V. Think about this.

    If Vb=4V and Ve=4V, then wouldn't Vb-Ve be 0V?

    So try again. You are on the right track. One you have the correct Ve, then it should be a simple matter to find Ie for Q1. With Ie, you should be able to find Ic and, from there, Vc very quickly.
     
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