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Homework Help: Unable to solve this simple BJT question! Help pls!

  1. Oct 5, 2011 #1
    1. As compared to the circuit as shown in the figure, i applied KCL in the circuit and still couldn't get the right Ic current at the collector as shown in the simulation.


    2. The IC current for XMM2 is 1.64mA but i got 22.12mA instead in my calculation. (I'm using the Ic=βIb where β=175 for the solution.)

    3. Ib= Vcc-Vbe/20k Ib=3-0.7/20k Ib=0.115mA Ic=Ib (175) Ic=22.12mA

    Any idea? Somehow, i need to explain it in my discussion for my report. I screwed up with the calculation and i have no idea of explaining the reason why Vce is approximately equal to 0 when there is a Ib current due to Vb voltage at its base.

    More info, XMM1 shows the voltage of 77.205mV....
  2. jcsd
  3. Oct 5, 2011 #2


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    Staff: Mentor

    You're operating the transistor in a non-linear region. Ic will not be β*Ib there.

    Suppose that the transistor was driven into saturation (turned on as hard as it can go). Then the collector-emitter voltage would be just about zero (looks like an "ON" switch). What would be the voltage across R1? What then its current?
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