Power Electronics Solved Objective Questions: Part-6

[1] The reverse recovery time of the diode is defined as the time between the instant diode current becomes zero and the instant reverse recovery current decays to
(a) Zero
(b) 10% of the reverse peak current (IRM)
(c) 25% of (IRM)
(d) 15% of (IRM)

Ans: C

[2] The cut-in voltage and forward-voltage drop of the diode are respectively
(a) 0.7V, 0.7V
(b) 0.7V, 1V
(c) 0.7V, 0.6V
(d) 1V, 0.7V

Ans: C

[3] The softness factor for soft-recovery and fast-recovery diodes are respectively
(a) 1, >1
(b) <1, 1
(c) 1, 1
(d) 1, <1

Ans: D

[4] Reverse recovery current in a diode depends on
(a) Forward field current
(b) Storage charge
(c) Temperature
(d) PIV

Ans:A

[5] The three terminals of power MOSFET
(a) Collector, Emitter, base
(b) Drain, source, base
(c) Drain, source, gate
(d) Collector, emitter, gate

Ans: C

[6]The three terminals of IGBT
(a) Collector, emitter, base
(b) Drain, source, base
(c) Anode, cathode, gate
(d) Collector, emitter, gate

Ans:D

[7] The three terminals of MCT
(a) Anode, cathode, gate
(b) Collector, emitter, gate
(c) Drain, source, base
(d) Drain, source, gate

Ans: A

[8] Compared to Power MOSFET, the Power BJT has
(a) Lower switching losses but higher conduction loss
(b) Higher switching losses and higher conduction loss
(c) Higher switching losses but lower conduction loss
(d) Lower switching losses and lower conduction loss

Ans:C

[9] Which one of the following statement is true
(a) MOSFET has positive temperature coefficient whereas BJT has negative temperature coefficient
(b) Both MOSFET and BJT have positive temperature coefficient
(c) Both MOSFET and BJT have negative temperature coefficient
(d) MOSFET has negative temperature coefficient whereas BJT has positive temperature coefficient

Ans:A

[10] Which one of the following statement is true
(a) Both MOSFET and BJT are voltage controlled devices
(b) Both MOSFET and BJT are current controlled devices
(c) MOSFET is a voltage controlled device and BJT is current controlled device
(d) MOSFET is a current controlled device and BJT is voltage controlled device

Ans: C . MOSFET operation is controlled by gate voltage and the BJT operation is controlled by base current

[11] Practical way of getting static voltage equalization in series connected SCRs is be the use of
(a) One resistor across the string
(b) Resistors of different values across each SCR
(c) Resistors of the same value across each SCR
(d) One resistor in series with the string
OPTIONS:
1) A & D
2) A
3) C
4) B
5) None of the above options

Ans: 3

[12] For series connected SCRs, dynamic equalizing circuit consists of
(a) Resistor R and capacitor C in series but with a diode D across C
(b) Series R and D circuit but with C across R
(c) Series R and C circuit but with D across R
(d) Series C and D circuit but with R across C
OPTIONS:
1) A
2) B
3) C
4) D
5) None of the above options

Ans: 3

[13] During forward blocking of two series connected SCRs, a thyristor with
(a) High leakage impedance shares lower voltage
(b) High leakage impedance shares higher voltage
(c) Low leakage impedance shares higher voltage
(d) Low leakage impedance shares lower voltage
OPTIONS:
1) B
2) D
3) B, D
4) A, C
5) None of the above options

Ans:3

[14] Thyristors A has rated gate current of 1A and thyristor B rated gate current of 100mA
(a) A is a GTO and B is a conventional SCR
(b) B is a GTO and A is a conventional SCR
(c) A may operate as a transistor
(d) B may be operate as a transistor
OPTIONS:
1) A
2) B
3) C
4) A, C
5) B, D

Ans: 4

[15] A resistor connected across the gate and cathode of an SCR increases its
(a) dv/dt rating
(b) Holding current
(c) Noise immunity
(d) Turn-off time
OPTIONS:
1) A, C
2) A, B
3) B, C
4) A, B, C
5) D

Ans: 4

Hint for Questions 5, 6, 7:
MOSFET:

IGBT

Remember that for IGBT we can represent the terminals either Drain, Source, Gate or Collector, Emitter, Gate.


MCT: