85.  In a single-phase converter with discontinuous conduction and extinction angle p > 7T, free-wheeling diode conducts for
A. a
B. 13 ? rc
C. 71 + a
D.13

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86.  In a single-phase converter with discontinuous conduction and extinction angle 13< TC, the free-wheeling diode conducts for
A. a
B.13?it
C. p ? TC
D. zero degree

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87. In single-phase semiconverter with continuous conduction, free-wheeling diode conducts for
A. a radians
B. (Tr ? a) radians
C. it radians
D. (it + a) radians

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88. In a single-phase semiconverter, for discontinu-ous conduction and extinction angle 13 < n, each SCR conducts for
A. a
B.13
C. it - a
D. - a

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89. In a single phase semiconverter, for discontinuous conduction and extinction angle 3> 71, each SCR conducts for
A. it ? a
B. (3 ? rc
C. a
D.13

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90. A free-wheeling doide is placed across the dc load
A. to prevent reversal of load voltage
B. to premit transfer of load current away from the source
C. both (a) and (b) above
D. none of the above

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91. An SCR fires at a minimum current of 80 mA at 65 ?C. The minimum current required to fire at 25 ?C is
A. < 80 mA
B. = 80 mA
C.> 80 mA
D. 40 mA

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