Exercise: Power Electronics

Questions for: Power Electronics

A single phase half wave regulator uses
A:
2 diodes and 2 thyristors
B:
2 thyristors
C:
1 diode and 1 thyristor
D:
2 diodes
Answer: C

Regulation is possible only in positive half cycle.

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When thyristors are connected in series and parallel, it may be necessary to have :
A:
current derating
B:
voltage derating
C:
both current and voltage derating
D:
none of the above
Answer: C

Thyristors in series do not share the voltage equally and require voltage derating. Thyristors in parallel need current derating.

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Which of these commutation methods is used in AC-DC converters?
A:
Class A
B:
Class C
C:
Class D
D:
Class F
Answer: D

Class F is natural commutation AC = DC converter use natural (or line) commutation.

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A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is
A:
25% of maximum
B:
50% of maximum
C:
75% of maximum
D:
none of the above
Answer: B

Conduction occurs only during 50% of wave.

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A thyristor has maximum allowable junction temperature of 110° C and the ambient temperature is 40°C, If the maximum internal power dissipation is 50 W, the thermal resistance is
A:
2° C/W
B:
1.4° C/W
C:
0.7°C/W
D:
2.2° C/W
Answer: B

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