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ECE :: Power Electronics

  1. If a step down chopper is fed by a dc voltage V with Ton and Toff are on and off periods then is

  2. A.
    average output voltage
    B.
    rms output voltage
    C.
    average or rms output voltage depending on load
    D.
    neither of the above

  3. A voltage VBB is applied across the terminals of a UJT. The emitter voltage at peak point is

  4. A.
    hVBB
    B.
    (h + 1) VBB
    C.
    hVBB + VD
    D.
    VD

  5. A single phase bridge type cycloconverter uses eight thyristors.

  6. A.
    True
    B.
    False

  7. In the circuit of figure, the waveshape of load current when thyristor conducting is

  8. A.
    constant
    B.
    increasing exponentially
    C.
    decreasing exponentially
    D.
    either (b) or (c)

  9. In the basic series inverter circuit, the source supplies load

  10. A.
    only in positive half cycle
    B.
    both in positive and negative half cycles
    C.
    only in part of positive half cycle
    D.
    in positive half cycle and part of negative half cycle

  11. A current source inverter has simple commutation circuit.

  12. A.
    True
    B.
    False

  13. In load commutated chopper, the commutating element

  14. A.
    is capacitor
    B.
    is capacitor and inductor
    C.
    is capacitor, inductor and auxiliary thyristor
    D.
    any of the above depending on load

  15. In a half bridge inverter each thyristor is gated at a frequency f. The output frequency is

  16. A.
    2 f
    B.
    f
    C.
    0.5 f
    D.
    0.25 f

  17. Assertion (A): A transistor has lower voltage drop during conduction as compared to thyristor

    Reason (R): Transistors are manufactured in very high voltage and current ratings.

  18. 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

  19. Assertion (A): Typical value of thermal resistance from source to sink of an SCR is about 0.3° C/W

    Reason (R): Heat sinks of thyristors are generally made of aluminium.

  20. 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