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Largest resistor value such that BJT remains in active mode

  1. Mar 9, 2014 #1
    1. The problem statement, all variables and given/known data
    We are given that the transistor has β = 30. The BJT is shown below (along with the solution). Every value in the figure is given with the exception of the equation I circled in red:

    3. The attempt at a solution
    What I don't get is how they got the inequality Vc - Vb > 0.4V? Where does this come from? I thought saturation occurs when Vce reaches 0.2V, so shouldn't our inequality be Ve - Vc > 0.2V?
  2. jcsd
  3. Mar 9, 2014 #2
    Assume that the magnitude of the base-emitter voltage for the BJT is largely constant. What value might you choose?
  4. Mar 9, 2014 #3


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    Staff: Mentor

    You are probably right. So at saturation what would be the voltage between C and B? Work it out for a silicon transistor.
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