Power Semiconductor Devices and Their Applications MCQs

Question 1

The average on-state current for an SCR is 20 A for a conduction angle of 120?. The average on-state current for 60? conduction angle will be

Accepted Answer

less than 20 A

Answer

20A

Answer

10 A

Answer

40 A

Question 2

The average on-state currentfor an SCR is 20A for a resistive load. If an inductance at 5 mH is included in the load, then average on-state current would be

Accepted Answer

more than 20 A

Answer

less than 20 A

Answer

15 A

Answer

20 A

Question 3

1n a conventional reverse blocking thyristor

Accepted Answer

the p-layers are lightly doped and the n-layer are heavily doped.

Answer

external layers are lightly doped and internal layers are heavily doped.

Answer

external layers are heavily doped and internal layers are lightly dooped

Answer

the p-layers are heavily doped and the n-layers are lightly doped

Question 4

In order to obtain static voltage equalization in series-connected SCRs, connections are made of

Accepted Answer

resistors of the same value across each SCR

Answer

one resistor acrossthe string

Answer

resistors of different values across each SCR

Answer

one resistor in series with the string

Question 5

Consider the following statements : The overlap angle of a phase-controlled converter would in crease on increasing the 1. supply voltage 2. suply frequency 3. load current 4. source inductance Of these statements

Accepted Answer

1, 2 and 4 are correct

Answer

1, 2 and 3 are correct

Answer

2, 3 and 4 are correct

Answer

1, 3 and 4 are correct

Question 6

Analysis of voltage waveform of a single phase bridge converter shows that it contains x% of 6th harmonic. The 6th harmonic content of the voltage waveform of a 3-phase bridge converter would be

Accepted Answer

greater than x% due to changes in the input and output voltages of the converter

Answer

less than x% due to an increase in the number of pulses

Answer

equal to x%, the same as that of the single phase converter

Answer

difficult to predict as the analysis of converters is not governed by any generalised theory

Question 7

Use of a reverse conducting thy ristor in place of antiparallel combination of thyristor and feedback diode in an inverter

Accepted Answer

causes deterioration in the commutation performance

Answer

effectively minimises the peak commutating current

Answer

in the rotor decreases the opeating frequency of operation

Answer

minimises the effects of lead inductances on the commutation performance

Question 8

A voltage source inverter is normally employed when

Accepted Answer

source inductance is small and load inductance is large

Answer

source inductance is large and load inductance is small

Answer

both source and load inductance are small

Answer

both source and load inductances are large

Question 9

Consider the following statements : The diodes in a voltage source inverter (Mc Murry inverter) should be able to 1. withstand a large voltage in the reverse direction 2. carry the commutating*current excess of load current. 3. provide the required reverse bias to the outgoing thyristor. 4. feedback the reactive current to the source Of these statements

Accepted Answer

2,3 and 4 are correct

Answer

1,2 and 3 are correct

Answer

1, 3 and 4 are correct

Answer

1,2 and 4 are correct