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ECE :: Power Electronics

  1. In a semi converter feeding a resistive load, the firing angle is a. Each thyristor conducts for

  2. A.
    p radians
    B.
    (p - a) radians
    C.
    (p + a) radians
    D.
    (p - 0.5 a) radians

  3. Between which points does UJT exhibit negative resistance characteristics

  4. A.
    between peak and valley points
    B.
    before peak point
    C.
    after peak point
    D.
    after valley point

  5. 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

  6. A.
    2° C/W
    B.
    1.4° C/W
    C.
    0.7°C/W
    D.
    2.2° C/W

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

  8. A.
    25% of maximum
    B.
    50% of maximum
    C.
    75% of maximum
    D.
    none of the above

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

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

  11. When thyristors are connected in series and parallel, it may be necessary to have :

  12. A.
    current derating
    B.
    voltage derating
    C.
    both current and voltage derating
    D.
    none of the above

  13. A single phase half wave regulator uses

  14. A.
    2 diodes and 2 thyristors
    B.
    2 thyristors
    C.
    1 diode and 1 thyristor
    D.
    2 diodes

  15. A Shockley diode can be used

  16. A.
    in place of SCR
    B.
    as a trigger switch for SCR
    C.
    in place of UJT
    D.
    both in place of SCR and as a trigger switch for SCR

  17. An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about

  18. A.
    2 μs
    B.
    5 μs
    C.
    20 μs
    D.
    50 μs

  19. In a multiphase chopper, the different choppers operate in

  20. A.
    series and all simultaneously
    B.
    parallel and one at a time
    C.
    parallel and simultaneously
    D.
    either (b) or (c)