BJT experts answer please...

Discussion in 'Homework Help' started by nPab, Sep 21, 2014.

  1. nPab

    Thread Starter New Member

    Sep 16, 2014
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    0
    The question is to find Ve, Vc1and Vc2 in the circuit below....I have no idea whatsoever on how to begin...please explain step by step...
    Thanks!
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Notice that Q2 base is connected directly to GND and Q1 base to 0.5V. If we assume that Vbe = 0.7V we immediately see that if we assume that Q1 is ON the Ve voltage must by equal to Vb + Veb = 0.5V + 0.7V = 1.2V and this implies that VebQ2 = 1.2V.
    But you should know that |Vbe| = 1.2V cannot happen without destroying the transistor. This implies that our assumption (about Q1 is turn on) was wrong. From here we see that Q1 is cut-off (VebQ1 = 0.7V - 0.5V = 0.2V) and Q2 is in active region or in saturation. So, now we can easily find all the voltage in the circuit. Can you do it ?
     
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  3. nPab

    Thread Starter New Member

    Sep 16, 2014
    5
    0
    Got it! thanks loads..:D
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    Just what I was gonna say. :)
     
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