For the transistor circuit shown in figure, evaluate VE,RB,RE, given IC=1mA,VCE=3V,VBE=0.5VandVCC=12V,β=100.

               

Hint: IC(RC+RE)+VCE=VCC and VB=VE+VBE
Step 1: Find the emitter resistance.
Consider the fig. (b) given here to solve this problem
ICIE[Asbasecurrentisverysmall.]
R=7.8
From the figure,
IC(RC+RE)+VCE=12
(RE+RC)×1×10-3+3=12
Step 3: Find the emitter voltage.
RE+RC=9×103=9
R=9-7.8=1.2
VE=IE×R
=1×10-3×1.2×103=1.2V
Step 3: Find the base voltage.
Voltage VB=VE+VBE=1.2+0.5=1.7V
CurrentI=VB20×103=1.720×103=0.085mA
Step 4: Find the base resistance.
ResistanceRB=12-1.7ICβ+0.085=10.30.01+0.085[Given,β=100]
=108