1
An SCR is turned off when its turn-off time is
A)
less than the circuit time constant
B)
greater than the circuit time constant
C)
less than the circuit turn-off time
D)
greater than the circuit turn-off time
Answer & Solution
Answer: Option
C
2
Which one of the following statements is NOT true?
A)
For SCRs to be in the conduction state, the forward anode current must be greater than the latching current
B)
For SCRs to be in the forward blocking state, the forward anode current must be lower than the holding current
C)
When SCRs are in the conduction state, they can be turned off by applying suitable gate pulses
D)
When avalance breakdown takes place, SCRs, enter into the conduction state
Answer & Solution
Answer: Option
C
3
The average on state current for an SCR is 20 A for a conduction angle of 120°. The average on-state current for 60° conduction angle will be
A)
20 A
B)
Less than 20 A
C)
10 A
D)
40 A
Answer & Solution
Answer: Option
B
4
Match
List-I with
List-II and select the correct answer.
List-I (Device)List-II (Property/item associated with it)
a. BJT
1. Pinch-off effect
b. FET
2. Controlled rectification
c. SCR
3. Negative resistance characteristics
d. Tunnel diode
4. Punch-through effect
A)
a-1, b-3, c-2, d-4
B)
a-1, b-2, c-3, d-4
C)
a-4, b-1, c-2, d-3
D)
a-1, b-4, c-3, d-2
Answer & Solution
Answer: Option
C
5
Which semiconductor power device out of the following is not a current triggered device?
A)
Thyristor
B)
GTO
C)
Triac
D)
MOSFET
Answer & Solution
Answer: Option
D
6
The purpose of connecting a Zener diode in a UJT circuit, used for triggering thyristors, is to
A)
expedite the generation of triggering pulses
B)
delay the generation of triggering pulses
C)
provide a constant voltage to UJT to prevent erratic firing
D)
provide a variable voltage to UJT as the source voltage changes
Answer & Solution
Answer: Option
C
7
When the pnpn diode is biased such that the p side is more positive than the n side, the junction J1 and J3 are:
A)
Forward biased
B)
Reverse biased
C)
Control biased
D)
Feedback biased
Answer & Solution
Answer: Option
A
8
A six pulse thyristor rectifier bridge is connected to a balanced 50 Hz, three phase AC source. Assuming that the DC output current of rectifier is constant, the lowest frequency harmonic component in the AC source line current is
A)
100 Hz
B)
150 Hz
C)
250 Hz
D)
300 Hz
Answer & Solution
Answer: Option
C
9
The triac can be used only in
A)
inverter
B)
rectifier
C)
chopper
D)
amplifier
Answer & Solution
Answer: Option
C
10
The turn-off time of thyristor is 30 µ sec at 50°C its turn-off time at 100°C will be
A)
same
B)
15 µ sec
C)
60 µ sec
D)
100 µ sec
Answer & Solution
Answer: Option
C
