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Power Electronics problems

  • 1. Assertion (A): An ideal rectifier should have unity harmonic factor

    Reason (R): An ideal rectifier should have unity displacement factor.


  • 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
    • Discuss
  • 2. A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is

  • Options
  • A. 20 W
  • B. 50 W
  • C. 92 W
  • D. 128 W
    • Discuss
  • 3. The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes

  • Options
  • A. about 100 times
  • B. about 10 times
  • C. about 3 times
  • D. about twice
    • Discuss
  • 4. The number of leads in an SCR are :

  • Options
  • A. 2
  • B. 3
  • C. 4
  • D. 5
    • Discuss
  • 5. Thyristors are not suitable for logic circuits.

  • Options
  • A. True
  • B. False
    • Discuss
  • 6. A cycloconverter can be

  • Options
  • A. step down
  • B. step up
  • C. step down or step up
  • D. none of the above
    • Discuss
  • 7. 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
    • Discuss
  • 8. In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is

  • Options
  • A. 333.33
  • B. 250
  • C. 500
  • D. 1000
    • Discuss
  • 9. 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 Is and rms value of load current in Irms. Then

  • Options
  • A. Is = Irms irrespective of the value of firing angle
  • B. Is = 0.5 Irms irrespective of the value of firing angle
  • C. Is = Irms if firing angle is less than 30°
  • D. Is = Irms if firing angle is more than 30°
    • Discuss
  • 10. 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
    • Discuss

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