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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.

    Untitled.jpg




    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

    gneill

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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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