BJT problem

Discussion in 'Homework Help' started by rthexton, May 24, 2009.

  1. rthexton

    Thread Starter New Member

    Sep 8, 2008
    5
    0
    Hi

    Can someone please help me with my homework for the attached circuit

    i need to find all the resistor values given the following

    Ic = 1ma
    Vre = 10%Vcc
    Hfe min = 110
    R2 = 0.1hfeminRe
    Vrc= 1/2(Vcc - Ve)

    If someone could show the steps involved it would be much appreciated!

    Cheers!
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    1. Assume Ie = Ic and Hfe = Hfe min
    2. Given Vre (= Ve) & Ie you can find Re
    3. Given Ve and Vcc, you can find Vrc and hence Rc (knowing Ic)
    4. Knowing Re gives you R2 - per question statement
    5. Given Ve and assuming Vbe = 0.65 (say) then you can find Vb
    6. Given Hfe and Ic you can find Ib
    7. Given Vb and R2 you can find Ir2
    8. Given Ir2 & Ib you can find Ir1
    9. Given Vcc, Vb and Ir1 you can find Vr1 and hence R1
     
  3. rthexton

    Thread Starter New Member

    Sep 8, 2008
    5
    0
    Thanks for your help TNK, i got the following values

    R1 = 14.9K
    R2 = 16.5K
    Rc = 12.85K
    Re = 1.5K

    I hope these are right!
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    Re and R2 look correct.

    Show how you got Rc and R1 and I or someone else will make a comment or suggestions.

    Hint:

    Did you use the relationship you were given to find Vrc -

    Vrc= 1/2(Vcc - Ve) ???

    What current values did you get for Ib and Ir2?
     
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