# Power Electronics Question and Answers – Power Transistor-1

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses 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

Explanation: 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

Explanation: 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) VBE
b) VCE
c) IB
d) IC

Explanation: 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

Explanation: 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) VBE
b) VCE
c) IB
d) IC

Explanation: The base current controls the collector current. Hence, the base current Ib is the controlling parameter.
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6. In a power transistor, the IB vs VBE curve is
a) a parabolic curve
b) an exponentially decaying curve
c) resembling the diode curve
d) a straight line Y = IB

Explanation: 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 IB is increased keeping VCE constant, then
a) IC increases
b) IC decreases
c) IC remains constant
d) none of the mentioned

Explanation: Ic is directly proportional to Ic.

8. The forward current gain α is given by
a) IC/IB
b) IC/IE
c) IE/IC
d) IE/IB

Explanation: 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) IC/IB
b) IC/IE
c) IE/IC
d) IE/IB

Explanation: 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

Explanation: When base-emitter & base-collector junctions are forward biased only than both the p-n junctions are forward biased and the device is on.

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