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Homework Help: Npn BJT question

  1. Mar 13, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine the mode of operation of this npn BJT, given the terminal voltages.

    E = -0.10 V
    B = 5.0 V
    C = 5.0 V

    2. Relevant equations


    3. The attempt at a solution

    According to the general rules, the EBJ is forward biased and the CBJ is reverse biased, leading to the conclusion that the device is in active mode. However, the values obtained (more below) do not make physical meaning. I just need to confirm my impression.

    V_BE = V_B - V_E = 5.0 - (-0.10) = 5.1 V

    V_CE = V_C - V_E = 5.0 - (-0.10) = 5.1 V

    V_BC = V_BE - V_CE = 0

    A typical V_BE is 0.7 V, and just 0.5 V is enough to forward bias EBJ; 5.1 V is way too much.

    Just over 0.3 V is enough to reverse bias CBJ; 5.1 V is way too much.

    If you plug this into current equations, they blow up to unrealistic values; it's not physical.

    Is this analysis correct?

  2. jcsd
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