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Power Electronics

51.

In a circuit using a full wave converter (M - 2 connection) the PIV of each thyristor is 400 V. For the same output voltage and fully controlled bridge converter, PIV will be

Answer: C

In bridge connection PIV is half of that in M-2 connection.

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52.

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

Answer: B

No Explanation.

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53.

A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is

Answer: B

Conduction occurs only during 50% of wave.

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54.

Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V.

Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

Answer: C

Junction temperature is about 120°C. Hence R is wrong.

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55.

Assertion (A): A TRIAC is a bidirectional SCR.

Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions.

Answer: A

Since a TRIAC can conduct in both directions it is bi directional SCR.

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Answer: B

Each thyristor conducts for 50% of time.

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57.

Which of these commutation methods is used in AC-DC converters?

Answer: D

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

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Answer: B

Value of C is proportional to maximum difference between reverse charge of SCRs in series.

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59.

A thyristor is reverse biased. A positive gate pulse is applied. The thyristor

Answer: C

Thyristor can turn on only when it is forward biased.

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60.

The waveshape of output voltage of half bridge inverter is

Answer: B

No answer description available for this question.

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