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Homework Help: BJT analysis

  1. Oct 31, 2016 #1
    1. The problem statement, all variables and given/known data
    Find Vc, Vb, Ve, Ib, Ic, and Ie
    Vbe is 0.7V


    2. Relevant equations

    3. The attempt at a solution
    Vb = (10*30k)/(80k) = 3.75V
    Ve = Vb-Vbe = 3.05V
    Ie = Ve/Re = 0.305A
    Icmax = 10/(1010) = 9.9mA
    Ie is much greater than 9.9mA, so this circuit is saturated. Is this correct?

    Attached Files:

  2. jcsd
  3. Oct 31, 2016 #2


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    Staff: Mentor

    This is true iff the base current is zero or negligible.

    It is better to apply Thévenin and say VB = 3.75 – IB×30k||50k

    Q still turns out to be saturated, yes.
  4. Nov 3, 2016 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    1. Substitute labels for the resistors, like R1, R2 etc. Substitute actual values only at the end.
    2. Write Σi = 0 at the base and emitter junctions. Let Ve = Vb - 0.75V. Gives you 4 independent equations in 4 unknowns.
    3. Assume no saturation and solve for ib, Vb, Ve and Vc. If Vc turns out to be < Ve your equations were invalid and you have saturation.
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