Quiz: Electrical Engineering
Exam: UPPSC AE
Topic: Power electronics (electrical engineering)
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute
Q1. A thyristor equivalent of thyratron tube is
(a) SCR
(b) UJT
(c) Diac
(d)Traic
Q2. An SCR is considered to be a semi-controlled device because
(a) it can be turned OFF but not ON with a gate pulse
(b) it conducts only during one half cycle of an alternating current wave.
(c) It can be turned ON but not OFF with a gate pulse.
(d) It can be turned ON only during one half cycle of an alternating voltage wave
Q3. In forward bias portion of the thyristor’s i-v characteristics, the number of stable operating region is
(a) One
(b)Two
(c) Three
(d) None
Q4. Turn-on of a thyristor takes place when
(a) anode to cathode voltage is positive
(b) anode to cathode voltage is negative
(c) there is a positive current pulse at the gate
(d) the anode to cathode voltage is positive and there is a positive current pulse at the gate
Q5. In the forward blocking region of a silicon-controlled rectifier, the SCR is
(a) In the off-state
(b) In the on-state
(c) reverse biased
(d) at the point of breakdown
Q6. Once an SCR is turned on, it remains so until the anode current goes below
(a) Triggering current
(b) Breakover current
(c) Threshold current
(d) Holding current
Q7. After firing an SCR, the gate pulse is removed. The current in the SCR will
(a) remain the same
(b) immediately fall to zero
(c) rise up
(d) rise a little and then fall to zero
Q8. When a thyristor is in ON state, its gate drive be
(a) removed to save power
(b) removed or may not be removed
(c) not removed as it will turn OFF the thyristor
(d) removed to avoid increased losses and higher junction temperature
Q9. In a thyristor the minimum current required to maintain the device in the ON state is called
(a) latching current
(b) ignition current
(c) holding current
(d) Avalanche current
Q10. In a thyristor the relation between the Holding current and latching current,
(a) more than latching current
(b) less than latching current
(c) equal to latching current
(d) equal to zero
Solutions
S1. Ans. (a)
Sol. SCR
S2. Ans. (c)
Sol. It can be turned ON but not OFF with a gate pulse.
S3. Ans. (b)
Sol. Two
S4. Ans. (d)
Sol. Turn-on of a thyristor takes place when the anode to cathode voltage is positive and there is a positive current pulse at the gate.
S5. Ans. (a)
Sol. In the forward blocking region of a silicon-controlled rectifier, the SCR is in the off-state.
S6. Ans. (d)
Sol. Once an SCR is turned on, it remains so until the anode current goes below Holding current.
S7. Ans. (a)
Sol. After firing an SCR, the gate pulse is removed. The current in the SCR will remain the same.
S8. Ans. (d)
Sol. removed to avoid increased losses and higher junction temperature
S9. Ans. (c)
Sol. Holding current
S10. Ans. (b)
Sol. less than latching current (IL)
