Power Semiconductor Devices and Their Applications MCQs

Question 1

A voltage source 200 sin 314t supplies resistive load of 50 ohms through a controlled thyristor which performs half-wave rectification. If the firing angle is 30? with respect to supply voltage waveform, the average poiver in the load is

Accepted Answer

76.6 watts

Answer

90.3 watts

Answer

80.3 watts

Answer

65.3 watts

Question 2

Snubber circuit is used to limit the rate of

Accepted Answer

rise of voltage across SCR

Answer

rise of current

Answer

conduction period

Answer

none of these

Question 3

The provision of a freewheeling diode across an indcutive load is

Accepted Answer

to avoid negative reversal voltage drop

Answer

to restore conduction angle on phase

Answer

to reduce the PRV

Answer

none of these

Question 4

In single-phase full-wave controlled bridge rectifier, maximum output voltages is obtained at ____ conduction angle and ____minimum at conduction angle?

Accepted Answer

0?, 180?

Answer

180?, 00

Answer

0?, 0?

Answer

180?, 180?

Question 5

A single-phase AC regulator with an inductance load has the following details Source voltage, 230 V, at a frequency of 50 Hz and coL = 5 ohms. The control range of the firing angle is

Accepted Answer

? < a < 71 2 ?

Answer

0 < a < TC

Answer

0 a < ?2

Answer

it < a < 2

Question 6

In a SCR,

Accepted Answer

the holding current is less or greater than latching current

Answer

the holding current is five times the latching current

Answer

the two currents are equal

Answer

the latching current is about 3 times the holding current

Question 7

A thyristor and transistor as a switch are compared. The true ones are

Accepted Answer

Thyristor requires turn off circuit while transistor does not.

Answer

The voltage drop of thyristor is less than transistor.

Answer

?Thyristor draws continuously base current.

Answer

none of the above

Question 8

A thyristor is in the forward blocking state. Then

Accepted Answer

the anode and cathode junctions are forward baised but the gate junction is reverse biased

Answer

all the 3 junctions are reverse biased

Answer

the anode junction is forward biased but the other two, cathode and gate junctions are reverse biased

Answer

the anode and gate junctions are forward biased but the cathode junction is reverse biased.

Question 9

The turn-off tune of a lhyristor is 30 sec at 50?C. It's run off time at 100? is

Accepted Answer

60p sec

Answer

same

Answer

l5 .t sec

Answer

100p sec