Electronics and Communication Engineering - Power Electronics

36. 

A single phase half wave controlled rectifier circuit has a free wheeling diode. The load is a combination of R and L. The firing angle is a. The period of conduction of SCR and free wheeling diode respectively are

A. a < ωt < p and p < ωt < (2p + a)
B. a < ωt < p and p < ωt < 2p
C. a < ωt < (p + a) and (p + a) < ωt < 2p
D. a < ωt < p and p < ωt < (2p - a)

Answer: Option A

Explanation:

SCR conducts from a to p and free wheeling diode from p to (2p + a).


37. 

Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.

Reason (R): Transistor find widespread application in power electronic circuits.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

Answer: Option C

Explanation:

Transistors are used but not very widely.


38. 

In a thyristor the gate current is increased, then

A. anode current will increase
B. anode current will decrease
C. anode current will remain constant
D. anode current may increase or decrease

Answer: Option C

Explanation:

Gate current does not affect the magnitude of anode current.


39. 

Thyristors are not suitable for logic circuits.

A. True
B. False

Answer: Option B

Explanation:

Thyristors can be used for logic circuits.


40. 

A single phase half wave rectifier is feeding a resistive load. Input voltage v = Vm sin ωt. The output dc voltage is Vdc and output rms voltage is Vrms . If firing angle is 180°, Vdc and Vrms respectively are

A. 0 and 0
B.
C. 0 and - Vm
D.

Answer: Option A

Explanation:

Put a = 180° in Eqs

Otherwise also a = 180° means no conduction.

Hence zero output voltage.