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ECE Objective Questions { Power Semiconductor Devices and Their Applications }

43. A triac
A. conducts when not triggered
B. conducts when not triggered in both directions
C. conducts whentriggered in one direction
D. none of the above

44. A voltage source 200 sin 314t is applied to a thyristor controlled half wave rectifier with resistive load of 50f/. If the firing angle is 30? with respect to supply voltage waveform, the average power in the load is
A. 90.6 watts
B. 86.3 watts
C. 60.8 watts
D. 70.6 watts.

45. RC snubber circuit is used to limit the rate of
A. rise of current in SCR
B. rise of voltage across SCR
C. conduction period
D. all of the above

46. A free wheeling diode is connected across as inductive load is
A. to restore conduction angle on phase
B. to avoid negative reversal voltage drop
C. to reduce the PRV
D. All of the above

47. Equalising circuits are provided across each SCR in series operation to provide uniform
A. current distribution
B. voltage distribution
C. firing of SCRs
D. all of the above

48. The thyristor is turned-off when the node current falls below
A. forward current
B. latching curi-ent
C. holding current
D. break over current

49. In a thyristor circuit, the angle of conduction is changed by changing
A. anode voltage
B. gate current
C. forward currer
D. anode current

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