250+ TOP MCQs on BJT DC biasing – Fixed Bias and Emitter Bias and Answers

Analog Circuits Multiple Choice Questions 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. I_B = β I_E
B. I_B = I_E
C. I_B = (β + 1) I_E
D. I_E = (β + 1) I_B

Answer: D
Clarification: For a BJT, the collector current I_C = βI_B and I_E = I_C + I_B
Hence, I_E = (β + 1) I_B.

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

Answer: A
Clarification: 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 I_BQ?

A. 47.08 mA
B. 47.08 uA
C. 50 uA
D. 0 mA

Answer: B
Clarification: Consider the BJT to be in saturation. Then I_C=12-0.2/2.2k=5.36 mA
And I_B=12-0.8/240k=0.047 mA
I_BMIN=I_CSAT/β=5.09/50=0.1072mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=12-0.7/240=47.08μA

4. From the given circuit, using a silicon BJT, what is the value of V_CEQ?

A. 7 V
B. 0.7 V
C. 6.83 V
D. 7.17 V

Answer: C
Clarification: Consider the BJT to be in saturation. Then I_C=12-0.2/2.2k=5.36 mA
And I_B=12-0.8/240k=0.047 mA
I_BMIN=I_CSAT/β=5.09/50=0.1072mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=12-0.7/240=47.08μA
I_C=50×47.08=2.354 mA
V_CE=V_CC-I_CR_C=12-2.354*2.2=12-5.178=6.83V.

5. From the given circuit, using a silicon BJT, what is the value of V_BC?

A. 6.13 V
B. -6.13 V
C. 7 V
D. -7 V

Answer: B
Clarification: Consider the BJT to be in saturation. Then I_C=12-0.2/2.2k=5.36 mA
And I_B=12-0.8/240k=0.047 mA
I_BMIN=I_CSAT/β=5.09/50=0.1072mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=12-0.7/240=47.08μA
I_C=50×47.08=2.354 mA
V_CE=V_CC-I_CR_C=12-2.354*2.2=12-5.178=6.83V
Hence V_BC = 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

Answer: B
Clarification: 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 V_CE = 0.2V and current is 12-0.2/2.2=5.36 mA.

7. In the given circuit, what is the value of I_C if the BJT is made of Silicon?

A. 2.01 mA
B. 2.01 uA
C. 10.05 mA
D. 10.05 uA

Answer: A
Clarification: Consider the BJT to be in saturation. Then I_C=20-0.2/2k=9.9 mA
And I_B=20-0.8/430k=0.044 mA
I_BMIN=I_CSAT/β=5.09/50=0.198mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=20-0.7/430=44.88μA
I_C=50×44.88=2.24 mA.

8. In the given circuit, using a silicon BJT, what is the value of V_CE?

A. 20 V
B. 15.52 V
C. 14.98 V
D. 13.97 V

Answer: b
Clarification: Consider the BJT to be in saturation. Then I_C=20-0.2/2k=9.9 mA
And I_B=20-0.8/430k=0.044 mA
I_BMIN=I_CSAT/β=5.09/50=0.198mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=20-0.7/430=44.88μA
I_C=50×44.88=2.24 mA
V_CE=20-2.24*2=15.52V.

9. In the given circuit, what is the value of V_E when using a silicon BJT?

A. 2.01 V
B. 0.28 V
C. 0 V
D. 2.28 V

Answer: D
Clarification: Consider the BJT to be in saturation. Then I_C=20-0.2/2k=9.9 mA
And I_B=20-0.8/430k=0.044 mA
I_BMIN=I_CSAT/β=5.09/50=0.198mA which is greater than above I_B.
Hence transistor is in the active region.
Thus I_C=βI_B.
V_BE=0.7V
I_B=20-0.7/430=44.88μA
I_C=50×44.88=2.24 mA
V_CE=20-2.24*2=15.52V
V_E=I_ER_E=(1+β)I_BR_E=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

Answer: C
Clarification: 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 V_CE = 0.2V and current is 20-0.2/2.2=9.9 mA.