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Department of Electronics and Communication Engineering
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Question 1 : For an UJT employed for the triggering of an SCR, stand -off ratio n =0.64 and do source voltage V BB os 20 V .The ujt would trigger when the voltage is
Option-1 :12.8 V
Option-2 :13.1 V
Option-3 :10 V
Option-4 :5 V
Question 2 : An SCR can withstand a maximum junction temperature of 120 degree with an ambient temperature of 75degree C, If this SCR has thermal resustance from junction to ambient as 1.5 degree /W,the maximum internal power dissipation allowed is
Option-1 :30 W
Option-2 :60 W
Option-3 :80 W
Option-4 :50 W
Question 3 : For dynamic equalizing circuit used for series connected SCRs,the choice of C is based on
Option-1 :reverse recovery characteristic
Option-2 :turn -on characteristics
Option-3 :turn-off characteristics
Option-4 :rise-time characteristics .
Question 4 : In an UJT,with Vbb as the voltage across two base terminals,the emitter potential at peak point is given by
Option-1 :n V BB
Option-2 :n V D
Option-3 :n V BB+V D
Option-4 :n V D+ V BB
Question 5 : An UJT exhibits negative resistance region
Option-1 :before the peak point
Option-2 :between peak and valley points
Option-3 :after the valley point
Option-4 :both (a) and (c)
Question 6 : In an UJT ,maximum value of charging resistance is associated with
Option-1 :peak point
Option-2 :valley point
Option-3 :any point between peak and valley points
Option-4 :after the valley point .
Question 7 : When an UJT is used for triggering an SCR, the waveshape of the voltage obtained from UJT circuit is a
Option-1 :sinr wave
Option-2 :saw-tooth wave
Option-3 :trapezoidal wave
Option-4 :square wave .
Question 8 : For an SCR di /dt protection is achieved through the use of
Option-1 :R in series with SCR
Option-2 :RL in series with SCR
Option-3 :L in series with SCR
Option-4 :L across SCR .
Question 9 : The function of snubber circuit connected across an SCR is to
Option-1 :suppress du /dt (b)
Option-2 :increase du /dt
Option-3 :decrease du /dt (d)
Option-4 :keep transient overvoltage at a constant value .
Question 10 : The object of connecting resistance and capacitance across gate circuit is to protect the SCR gate against
Option-1 :overvaltages
Option-2 :du /dt
Option-3 :noise signals
Option-4 :overcurrents
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