Power Semiconductor Devices and Their Applications MCQs

Question 1

Select the correct statement(s)

Accepted Answer

All of these

Answer

The triac is a five-layer device.

Answer

The traic may be considered to consist

Answer

An additional lateral n-region serves p2 and pi ? n2 ? p2 ? n3. of two parallel section ni ? p1 ? n2 ?as control gate.

Question 2

There are only silicon controlled rectifiers and not germanium because

Accepted Answer

only Si has as stable off state

Answer

Si is avilable as compared to Ge

Answer

Ge is very temperature sensitive

Answer

None of the above

Question 3

In a single-phase' full-wave SCR circuit with R,L load

Accepted Answer

the negative dc voltage is maximum at a= 180?

Answer

power is delivered to the source for delay angles of less than 90?

Answer

the SCR changes from inverter to converter at a = 90?

Answer

to turn off the thyristor, the maximum delay angle must be less than 1800

Question 4

A triac and SCR are compared

Accepted Answer

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

Answer

Both are unidirectional devices

Answer

A triac has less time for turn off than SCR

Answer

Both are aviiable with comparable voltage and current ratings

Question 5

Once SCR starts conducting a forward current, its gate losses controlover

Accepted Answer

anode circuit voltage and current

Answer

anode circuit voltage only

Answer

anode circuit current only

Answer

anode circuit voltage, current and time

Question 6

In a thyristor, the magnitude of anode current will

Accepted Answer

not change with any variation in gate current

Answer

increase if gate current is increased

Answer

decrease if gate current is decreased

Answer

increase if gate current is decreased

Question 7

Turn-on time of an SCR in series with RL circuit can be reduced by

Accepted Answer

decreasing L

Answer

increasing circuit resistance R

Answer

decreasing R

Answer

increasing circuit inductance L

Question 8

Specification sheet for a SCR gives its maximum rms on-state current as 35 A. This rms rating for a conduction angle of 120? would be

Accepted Answer

35 A

Answer

more than 35 A

Answer

less than 35 A

Answer

52.5 A

Question 9

For a UJT employed for the triggering of an SCR, stand-off ratio n = 0.64 and dc source voltage V 20 V. The UJT would trigger when the emitter votlage is

Accepted Answer

13.1V

Answer

12.8 V

Answer

10 V

Answer

5 V