Power Electronics Special MCQ Part Six

Power Electronics Special MCQ Part Six

Power Electronics Special MCQ Part Six

1.In forward bias portion of the thyristor’s I – V characteristics, the number of stable operating regions is
(A) One
(B) Two
(C) Three
(D) None

Answer-B

2.A reverse conducting thyristor (RCT) normally replaces
(A) A pair of anti parallel thyristors in a circuit
(B) A combination of thyristor and an anti parallel diode in a circuit
(C) A thyristor in saturation where it is not required to have reverse blocking capability at all
(D) Conventional conversion grade thyristors having large turn off time

Answer-C

3.A structure obtained by lightly doped n – drift region between the layers of a pn junction, a PIN diode is obtained. This structure is effective in
(A) Making the diode support large reverse blocking voltages
(B) Making reverse recovery process slow
(C) Making the diode have high on state voltage drop
(D) Reducing the voltage spike during turn off due to stray inductance

Answer-A

4.Which of the following statements is not correct for a MOSFET?
(A) Are easy to parallel for higher currents
(B) Leakage current is relatively high
(C) Have more linear characteristics
(D) Overload and peak current handling capability are high

Answer-B

5.For an SCR, the gate cathode characteristic has a straight line slope of 140. For trigger source voltage of 20 V and allowable gate power dissipation of 0.5 W, What is the gate source resistance?
(A) 200 Ω
(B) 255 Ω
(C) 195 Ω
(D) 185 Ω

Answer-C

Power Electronics Special MCQ Part Six

6.When compared to those of a symmetrical thyristor, the turn off time and reverse blocking voltage of an asymmetrical thyristor are respectively
(A) large and large
(B) large and small
(C) small and large
(D) small and small

Answer-D

7.If the amplitude of the gate pulse to thyristor is increased, then
(A) both delay time and rise time increases
(B) the delay time would increase and rise time would decrease
(C) the delay time would decrease and rise time would increase
(D the delay time would decrease and rise time remains unaffected

Answer-D

8.How many SCRs are to be connected in series with 800 V rating to be used for a 3 kV circuit using de rating factor of 15%?
(A) 3
(B) 4
(C) 5
(D) 6

Answer-C

9.The transition capacitance of a diode is 1 nF and it can withstand a reverse potential of 400 V. A capacitance of 2 nF which can withstand a reverse potential of 1 kV is obtained by connecting
(A) two 1 nF diodes in parallel
(B) six parallel branches with branch comprising three 1 nF diodes in series
(C) two 1 nF diodes in series
(D) three parallel branches with branch comprising six 1 nF diodes in series

Answer-B

Power Electronics Special MCQ Part Six

10.An LASCR
(A) can conduct in both directions
(B) has a built in anti parallel diode
(C) is preferred in high voltage and high current applications where optical isolation is used between trigger source and switching device
(D) can be turned off by negative gate signal

Answer-C

11.Match List I with List II and select the correct answer using the codes given below the list

List I
P. TRIAC
Q. RCT
R. GTO
S. Amplifying gate thyristor

List II
1. good di/dt behavior even at low gate currents
2. Normally provided with a small continuous negative
Gate pulse during off state
3. Negative gate current for reverse conduction
4. No gate pulse for reverse conduction

(A) P – 4, Q – 3, R – 1, S – 2 (B) P – 3, Q – 4, R – 2, S – 1
(C) P – 3, Q – 4, R – 1, S – 2 (D) P – 4, Q – 3, R – 2, S – 1

Answer-B

12.SCR is more utilized as compared to a Triac because
(A) more capable in regard to control
(B) more efficient
(C) available with higher ratings
(D) comparatively cheaper

Answer-A,C

13.If a diode is connected in anti parallel with thyristor, then
(A) both turn off power loss and turn off time decreases
(B) turn off power loss decreases and turn off time increases
(C) turn off power loss increases and turn off time decreases
(D) none of the above

Answer-A

Power Electronics Special MCQ Part Six

14.A Darlington pair consisting of two power transistors has an effective b of 125. If the driver BJT has a b of 20, the b of the main transistor is
(A) 5
(B) 25
(C) 65
(D) 100

Answer-A

15.A thyristor (SCR) turns off when
(A) Gate pulse is removed
(B) Gate pulse is applied
(C) Thyristor current is below holding value
(D) Anode voltage is made negative

Answer-C

16.A triac is device which acts as a
(A) Diode in the forward direction and thyristor in reverse direction
(B) Thyristor in both directions
(C) Diode in both directions
(D) Thyristor in the forward direction and diode in reverse direction

Answer-D

17.Which of the following power semi conductor device has bipolar capability?
(A) SCR
(B) MOSFET
(C) IGBT
(D) BJT

Answer-A

Power Electronics Special MCQ Part Six

18.Which of the following transistors is symmetrical in the sense that emitter and collector or source and drain terminals can be interchanged?
(A) JFET
(B) MOSFET
(C) NPN transistor
(D) PNP transistor

Answer-B

19.The snubber circuit used to shape the turn on switching trajectory of thyristor and/or to limit dv/dt during turn off is
(A) L – R snubber polarized
(B) R – C snubber polarized
(C) R – C snubber un polarized
(D) L – R snubber un polarized

Answer-B

20.When a thyristor is in the forward blocking state, then
(A) All 3 junctions are reverse biased
(B) Anode and cathode junctions are forward biased and gate junctions reverse biased
(C) Anode junction is forward biased but other two reverse biased
(D) Anode and gate junctions are forward biased and cathode junction is reverse biased

Answer-B

Power Electronics Special MCQ Part Six