Assertion (A): Power transistor has lower switching time than SCR Reason (R): Po

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Question
Assertion (A): Power transistor has lower switching time than SCR
Reason (R): Power transistor has greater switching time than SCR
Options
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

Correct Answer

A is wrong but R is correct

Explanation

Power transistor does not have high

Assertion (A): Power transistor has lower switching time than SCR Reason (R): Power transistor has g

rating.

Power Electronics problems

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1. A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is I_s and rms value of load current in I_rms. Then
Options
A. I_s = I_rms irrespective of the value of firing angle
B. I_s = 0.5 I_rms irrespective of the value of firing angle
C. I_s = I_rms if firing angle is less than 30�
D. I_s = I_rms if firing angle is more than 30�

2. In a step down chopper using pulse width modulation, T_on = 3 x 10^-3 and T_off = 1 x 10^-3 s. The chopping frequency is
Options
A. 333.33
B. 250
C. 500
D. 1000

3. For a 12 pulse operation, the two 6 pulse units are fed by
Options
A. Y - Y and Y - Y transformers
B. ? - ? and ? - ? transformers
C. Y - Y and Y - ? transformers
D. Y - ? and Y - ? transformers

6. In a single phase full wave converter (M-2 connection) feeding on R - L load, the input voltage is v = V_m sin ?t. The expression for dc output voltage is
Options
A.
B.
C.
D.

7. An SCR is triggered at 40� in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80�, the average anode current is likely to be
Options
A. 50 A
B. 25 A
C. less than 50 A but more than 25 A
D. less than 25 A

8. Assertion (A): The surge current which an SCR can withstand is much higher than rms on state current.
Reason (R): The duration of surge current is very small.
Options
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

9. 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
Options
A. a < ?t < p and p < ?t < (2p + a)
B. a < ?t < p and p < ?t < 2p
C. a < ?t < (p + a) and (p + a) < ?t < 2p
D. a < ?t < p and p < ?t < (2p - a)

10. A thyristor has a turn on time of 6 ?s. If the anode circuit is inductive, the turn on time will be
Options
A. 6 ?s
B. less than 6?s
C. more than 6 ?s
D. either 6 ?s or less

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