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ECE :: Power Electronics

  1. In a single phase full wave ac regulator feeding R-L load, the gate pulses

  2. A.
    are always of short duration
    B.
    may be of short duration
    C.
    should be rectangular with width (p - a)
    D.
    cannot be rectangular with width (p - a)

  3. In a semi converter feeding a resistive load,

  4. A.
    the waveshapes of input voltage and input current are always similar
    B.
    the waveshapes of input voltage and input current can never be similar
    C.
    the waveshapes of input voltage and input current are similar only if firing angle is zero
    D.
    the waveshapes of input voltage and input current are similar only if firing angle is high

  5. In a single phase semi-converter the number of thyristors is

  6. A.
    16
    B.
    8
    C.
    4
    D.
    2

  7. A dc chopper is feeding an RLE load. The current can become discontinuous if

  8. A.
    is high
    B.
    a is low
    C.
    E is high
    D.
    none of the above

  9. Which of these commutation methods uses two leads?

  10. A.
    Class A
    B.
    Class B
    C.
    Class C
    D.
    Class D

  11. A single phase half wave rectifier is feeding a resistive load. As firing angle is increased

  12. A.
    dc output voltage and rms output voltage decrease in the same proportion
    B.
    dc output voltage and rms output voltage decrease
    C.
    dc output voltage and rms output voltage increase
    D.
    dc output voltage and rms output voltage increase in the same proportion

  13. A cycloconverter for single phase operation has

  14. A.
    one positive group and one negative group converters
    B.
    two positive group and two negative group converters
    C.
    three positive group and three negative group converters
    D.
    any of the above

  15. A chopper is a high efficiency circuit.

  16. A.
    True
    B.
    False

  17. The difference between resonant commutation and self commutation is

  18. A.
    both these methods are based on entirely different principles
    B.
    in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current
    C.
    resonant commutation uses L and C but self commutation uses only capacitor
    D.
    none of the above

  19. If 0.5 T is the time period of oscillations and Toff is the time between turn off of one thyristor and turn on of second thyristor, the frequency of output f of a series inverter is