Power Electronics Question and Answers – Power Transistor-1 and Answers

Power Electronics Multiple Choice Questions on “Power Transistors – 1”

1. Which of the following devices does not belong to the transistor family?
A. IGBT
B. MOSFET
C. GTO
D. BJT
Answer: C
Clarification: GTO is gate turn off transistor, it belongs to the Thyristor family. All the other devices belong to the transistor family.

2. A power transistor is a
A. three layer, three junction device
B. three layer, two junction device
C. two layer, one junction device
D. four layer, three junction device
Answer: B
Clarification: It has three layers p-n-p or n-p-n forming two p-n junctions.

3. In a power transistor, ____ is the controlled parameter.
A. V_BE
B. V_CE
C. I_B
D. I_C
Answer: D
Clarification: The collector current is the controlled parameter.

4. A power transistor is a _________ device.
A. two terminal, bipolar, voltage controlled
B. two terminal, unipolar, current controlled
C. three terminal, unipolar, voltage controlled
D. three terminal, bipolar, current controlled
Answer: D
Clarification: Power transistor is simply many BJT’s connected in series parallel on a single silicon chip for power applications. It is a three terminal, bipolar, current controlled device.

5. In a power transistor, _________ is the controlling parameter.
A. V_BE
B. V_CE
C. I_B
D. I_C
Answer: C
Clarification: The base current controls the collector current. Hence, the base current Ib is the controlling parameter.

6. In a power transistor, the I_B vs V_BE curve is
A. a parabolic curve
B. an exponentially decaying curve
C. resembling the diode curve
D. a straight line Y = I_B
Answer: C
Clarification: The B-E junction of a BJT resembles a p-n junction diode, hence the curve.

7. For a power transistor, if the base current I_B is increased keeping V_CE constant, then
A. I_C increases
B. I_C decreases
C. I_C remains constant
D. none of the mentioned
Answer: A
Clarification: Ic is directly proportional to Ic.

8. The forward current gain α is given by
A. I_C/I_B
B. I_C/I_E
C. I_E/I_C
D. I_E/I_B
Answer: B
Clarification: Collector current by emitter current is the current gain, its value is close to one but never greater than.

9. The value of β is given by the expression
A. I_C/I_B
B. I_C/I_E
C. I_E/I_C
D. I_E/I_B
Answer: A
Clarification: Collector current by the base current is beta, its value is in the range 50 to 300.

10. A power BJT is used as a power control switch by biasing it in the cut off region (off state) or in the saturation region (on state). In the on state
A. both the base-emitter & base-collector junctions are forward biased
B. the base-emitter junction is reverse biased, and the base collector junction is forward biased
C. the base-emitter junction is forward biased, and the base collector junction is reversed biased
D. both the base-collector & the base-emitter junctions are reversed biased
Answer: A
Clarification: When base-emitter & base-collector junctions are forward biased only than both the p-n junctions are forward biased and the device is on.