This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “BJT DC biasing – Fixed Bias and Emitter Bias”.
1. Which of the following is the correct relationship between base and emitter current of a BJT?
a) IB = β IE
b) IB = IE
c) IB = (β + 1) IE
d) IE = (β + 1) IB
View Answer
Explanation: For a BJT, the collector current IC = βIB and IE = IC + IB
Hence, IE = (β + 1) IB.
2. For best operation of a BJT, which region must the operating point be set at?
a) Active region
b) Cutoff region
c) Saturation region
d) Reverse active region
View Answer
Explanation: Operating point for a BJT must always be set in the active region to ensure proper functioning. Setting up of Q-point in any other region may lead to reduced functionality.
3. From the given circuit, using a silicon transistor, what is the value of IBQ?
a) 47.08 mA
b) 47.08 uA
c) 50 uA
d) 0 mA
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=12-0.2/2.2k=5.36 mA
And IB=12-0.8/240k=0.047 mA
IBMIN=ICSAT/β=5.09/50=0.1072mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=12-0.7/240=47.08μA
4. From the given circuit, using a silicon BJT, what is the value of VCEQ?
a) 7 V
b) 0.7 V
c) 6.83 V
d) 7.17 V
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=12-0.2/2.2k=5.36 mA
And IB=12-0.8/240k=0.047 mA
IBMIN=ICSAT/β=5.09/50=0.1072mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=12-0.7/240=47.08μA
IC=50×47.08=2.354 mA
VCE=VCC-ICRC=12-2.354*2.2=12-5.178=6.83V.
5. From the given circuit, using a silicon BJT, what is the value of VBC?
a) 6.13 V
b) -6.13 V
c) 7 V
d) -7 V
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=12-0.2/2.2k=5.36 mA
And IB=12-0.8/240k=0.047 mA
IBMIN=ICSAT/β=5.09/50=0.1072mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=12-0.7/240=47.08μA
IC=50×47.08=2.354 mA
VCE=VCC-ICRC=12-2.354*2.2=12-5.178=6.83V
Hence VBC = 0.7-6.83 = -6.13V.
6. From the given circuit, using silicon BJT, what is the value of the saturation collector current?
a) 5 mA
b) 5.36 mA
c) 5.45 mA
d) 10.9 mA
View Answer
Explanation: To obtain an approximate answer, undersaturation the BJT is ON and hence acts as a short circuit. However, ideally a drop exists for the transistor which is a fixed value. For an exact answer, if the BJT is a Silicon transistor, then drop VCE = 0.2V and current is 12-0.2/2.2=5.36 mA.
7. In the given circuit, what is the value of IC if the BJT is made of Silicon?
a) 2.01 mA
b) 2.01 uA
c) 10.05 mA
d) 10.05 uA
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=20-0.2/2k=9.9 mA
And IB=20-0.8/430k=0.044 mA
IBMIN=ICSAT/β=5.09/50=0.198mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=20-0.7/430=44.88μA
IC=50×44.88=2.24 mA.
8. In the given circuit, using a silicon BJT, what is the value of VCE?
a) 20 V
b) 15.52 V
c) 14.98 V
d) 13.97 V
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=20-0.2/2k=9.9 mA
And IB=20-0.8/430k=0.044 mA
IBMIN=ICSAT/β=5.09/50=0.198mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=20-0.7/430=44.88μA
IC=50×44.88=2.24 mA
VCE=20-2.24*2=15.52V.
9. In the given circuit, what is the value of VE when using a silicon BJT?
a) 2.01 V
b) 0.28 V
c) 0 V
d) 2.28 V
View Answer
Explanation: Consider the BJT to be in saturation. Then IC=20-0.2/2k=9.9 mA
And IB=20-0.8/430k=0.044 mA
IBMIN=ICSAT/β=5.09/50=0.198mA which is greater than above IB.
Hence transistor is in the active region.
Thus IC=βIB.
VBE=0.7V
IB=20-0.7/430=44.88μA
IC=50×44.88=2.24 mA
VCE=20-2.24*2=15.52V
VE=IERE=(1+β)IBRE=51*44.88*1=2.28V.
10. In the given circuit using a silicon BJT, what is the value of saturation collector current?
a) 10 mA
b) 8.77 mA
c) 6.67 mA
d) 5 mA
View Answer
Explanation: To obtain an approximate answer, under saturation the BJT is ON and hence acts as a short circuit. However, ideally a drop exists for the transistor which is a fixed value. For an exact answer, if the BJT is a Silicon transistor, then drop VCE = 0.2V and current is 20-0.2/2.2=9.9 mA.
Sanfoundry Global Education & Learning Series – Analog Circuits.
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