1.If the gating circuits generator negative pulses, then those can be removed by using
a) schmit triggers
b) clippers
c) clampers
d) zener diodes
Explanation: The clippers can be used to clip the negative part.
2. The improved version of the UJT oscillator triggering circuit is the
a) ramp & pedal triggering
b) rc triggering
c) cosine-pulse triggering
d) ramp triggering
Explanation: The ramp & pedal triggering is the improved version of the UJT oscillator triggering circuit.
3. RB1 = 3 kΩ & RB2 = 6 kΩ. Find the intrinsic stand-off ratio (η) of the UJT.
a) 9
b) 1/3
c) 2/3
d) 3
Explanation:
η = RB1/(RB1+RB1).
4. The decaying factor in the wave shape of the output pulses from the pulse transformer is its
a) transformer ratio
b) inductance
c) capacitance
d) resistance
Explanation: L is the decaying factor in the waveform which emerges from the PT.
5. The thyristor turn-off requires that the anode current
a) falls below the holding current
b) falls below the latching current
c) rises above the holding current
d) rises above the latching current
Explanation : For effective turn-off of the SCR the anode current must fall below the holding current value.
6. In case of class A type commutation or load commutation with low value of R load the
a) L is connected across R
b) L-C is connected across R
c) L is connected in series with R
d) L-C is connected in series with R
Explanation: In case of Class A commutation the requirement is that the circuit should be an under-damped RLC circuit.
7. The class A commutation or load commutation is possible in case of
a) dc circuits only
b) ac circuits only
c) both DC and AC circuits
d) none of the above mentioned
Explanation: The nature of the circuit should be such that when energized from the source, current must a a natural tendency to decay to zero for load commutation to occur in a SCR circuit.
8. In case of class B commutation or resonant-pulse commutation with L = 5 μH and C = 20 μC with initial voltage across the capacitor (Vs) = 230 V. Find the peak value of resonant current.
a) 560 A
b) 460 A
c) 360 A
d) 260 A
Explanation: Ip = Vs x √C/L.
9. In case of class B commutation or resonant-pulse commutation with L = 5 μH and C = 20 μC with the initial voltage across the capacitor (Vs) = 230 V. Find the conduction time for auxiliary thyristor.
a) 0.23 μs
b) 6.57 μ
c) 31.41 μs
d) 56 μs
Explanation: Ip = Vs x √C/L
ω = 1/√LC
t = π/ω.
10. An SCR is connected in series with L = 5 mH and C = 20 μF. Find the resonant frequency of the circuit.
a) 2569 rad/s
b) 3162 rad/s
c) 2400 rad/s
d) 7889 rad/s
Explanation: ω = 1/√LC.