BJT problem

Discussion in 'Homework Help' started by sportguy98, Nov 10, 2013.

  1. sportguy98

    Thread Starter New Member

    Sep 10, 2013
    5
    0
    Hello,

    I am having difficulty with this particular problem involving a BJT circuit. I was able to solve all other BJT problems except for this one.

    The teacher does give the solutions in hints, but I would like to understand why it is solved this way.

    Here is the problem:

    [​IMG]

    I wrote all the KVL equations... so KVL for base-emitter, KVL for base-collector and KVL for emitter-collector.

    I also know all the formulas like IE = IB + IC, IC = B*IB, IC = A * IE, etc.

    My problem is with the R1 and R2 resistances. If one them was grounded I would not have any trouble, but since they are, I do not know how to proceed or what simplifications to be made.

    Thanks again !
     
  2. LvW

    Active Member

    Jun 13, 2013
    674
    100
    My problem is with the R1 and R2 resistances. If one them was grounded I would not have any trouble, but since they are, I do not know how to proceed or what simplifications to be made.

    The two resistors form a voltage divider - if one of them is grounded or not.
    There is - in principle - no difference in the calculation method.
    However, you should be aware that you are free to choose a suitable impedance niveau for both resistors. A common rule of thumb is that the current through R1 is selcted to be approximately 10*Ib=10*Ic/80.
     
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