# BJT problem

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

1. ### rthexton Thread Starter New Member

Sep 8, 2008
5
0
Hi

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!

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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
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
790
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?