Power Semiconductor Devices and Their Applications MCQs

Question 1

Comparing a triac & SCR,

Accepted Answer

triac requires more current for turn on than SCR at a particular voltage

Answer

both are unidirectional devices

Answer

a tric a has less time for turn off than SCR

Answer

both are bidirectional devices

Question 2

In a thyristor

Accepted Answer

the turn-on time isless turn-off time

Answer

the turn-off time of a thyristor is less than turn-on time

Answer

the turn-off time for the line commutation is less than forced commutation

Answer

none of the above

Question 3

In a three phase halfwave diode rectifier, the ratio of average output voltage to per phase maximum ac voltage is

Accepted Answer

0.827

Answer

1

Answer

1.169

Answer

1.571

Question 4

Each diode in, half wave diode rectifier conducts for

Accepted Answer

1200

Answer

30?

Answer

60?

Answer

900

Question 5

In a semi converter, for firing angle less than or equal to 60?, wheeling diode conducts for

Accepted Answer

zero degree

Answer

30?

Answer

(b) 45?

Answer

75?

Question 6

In a full converter, 6 SCRs are fired at an interval of

Accepted Answer

120?

Answer

0?

Answer

60?

Answer

180?.

Question 7

The function of connecting a zener diode in a UJT circuit used for triggering of SCRs is to

Accepted Answer

provide a constant voltage to UJT to prevent erratic firing

Answer

expedite the generation of triggering pulses

Answer

delay the generation of triggering pulses

Answer

provide a variable voltage to UJT as the source voltage changes.

Question 8

The metal oxide variator (MOV) is used for protecting

Accepted Answer

anode circuit against overvoltage

Answer

gate circuit against overcurrents

Answer

gate circuit against overvoltages

Answer

anode circuit overcurrents

Question 9

In a GTO, anode current begins to fall when gate current

Accepted Answer

none of these

Answer

is negative peak at time t = 0

Answer

is negative peak at time t = storage time ts

Answer

just begins to become negative at t = 0