Extra Problems for BJT
Faculty of Information Engineering & Technology
Semiconductors (ELCT503)
IET Department
Dr. Hany Bastawrous
Winter 2011
Eng. Ahmed Ragheb
____________________________________________________________________________________
Problem Set 9
1. (a) The transistor shown on the right in the circuit has a very high β. Find
VE and VC for VB (i) +2 V, (ii) +1 V, and (iii) 0 V. Assume VBE = 0.7 V. (b)
Find the highest value of VB for which the transistor still operates in the active
mode. Also, find the value of VB for which the transistor operates in saturation
with a forced β of 1.
2. For the transistor shown on the left, assume α =1.
What are the values of VE and VC for VB = 0 V? For
what value of VB does the transistor cut off? Saturate?
In each case, what values of VE and VC result?
3. In the circuit shown on the right the transistor has β = 30. Find
the values of VB, VE, and VC. If RB is raised to 270 kΩ, what
voltages result? With RB = 270 kΩ, what value of β would return
the voltages to the values first calculated?
All the problems in the problem set are taken from Microelectronic Circuits 5th edition by Sedra/Smith.
4. For the circuits shown below, find values for the labelled node voltages and branch currents. Assume β
to be very high and VBE= 0.7 V for npn and VEB= 0.7 V for pnp transistors. (b) Repeat the analysis of the
circuits for β = 100. Find all the labelled node voltages and branch currents.
5. In the circuit shown on the right, VBE is adjusted so that VC = 2V.
If VCC = 5V, RC = 3 kΩ, and a signal vbe = 0.005sinωt volts is
applied, find expressions for the total instantaneous quantities iC(t),
vC(t), and iB(t). The transistor has β = 100. What is the voltage
gain?
All the problems in the problem set are taken from Microelectronic Circuits 5th edition by Sedra/Smith.
6. For the circcuit shown below,
b
α = 0.99. Usingg the
brid-π modeel, draw an AC
A equivaleent of the cirrcuit
hyb
sho
own. What is
i the input resistance
r
Rin
e the
i ? Calculate
overall voltagee gain (vo/vs).
he circuit shhown on thee left, the traansistor
7. In th
has a β of 200. W
What is the dc voltage at the
collecto
or? Find thee input resisstances Ri1 and
a Ri2
and thee overall vooltage gain (vo/vs). For output
signal of
o ± 0.4 V, what
w value of
o vs is requirred?
mitter-followeer circuit shhown
8. For the em
t BJT used
d is specifieed to
on the right, the
00 (a
havve β values in the rangee of 40 to 20
disstressing situation fo
or the ciircuit
dessigner). For the two extrreme values of β
(β = 40 and β = 200), find::
(a)) IE, VE, and VB.
(b)) the voltagee gain vo/vs.
All the
t problems inn the problem set are taken frrom Microelecctronic Circuitss 5th edition byy Sedra/Smith.