1. In a single-phase full converter feeding a highly inductive load, the current is
A) Sinusoidal
B) Constant
C) Pulsating
D) Discontinuous
Answer: B) Constant
2. In a three-phase half-wave converter, the output voltage ripple frequency is
A) Same as supply frequency
B) Twice supply frequency
C) Thrice supply frequency
D) Six times supply frequency
Answer: C) Thrice supply frequency
3. The conduction period of each thyristor in a 3-phase full converter is
A) 60°
B) 90°
C) 120°
D) 180°
Answer: D) 180°
4. The main function of freewheeling diode in a converter is to
A) Improve commutation
B) Reduce harmonics
C) Maintain current continuity
D) Reduce output voltage
Answer: C) Maintain current continuity
5. In a step-down chopper, if duty cycle is 0.4 and input is 200 V, output voltage is
A) 80 V
B) 120 V
C) 200 V
D) 400 V
Answer: A) 80 V
6. For a buck converter, the output voltage increases if
A) Duty cycle increases
B) Duty cycle decreases
C) Frequency decreases
D) Inductance decreases
Answer: A) Duty cycle increases
7. In a boost converter, the output voltage is
A) Less than input
B) Equal to input
C) Greater than input
D) Same as input
Answer: C) Greater than input
8. A chopper working at 2 kHz with 50% duty ratio is supplied with 100 V. Average output is
A) 25 V
B) 50 V
C) 100 V
D) 200 V
Answer: B) 50 V
9. In class-C chopper, the direction of load current is
A) Unidirectional
B) Bidirectional
C) Zero
D) Alternating
Answer: B) Bidirectional
10. The purpose of commutation in power electronics is
A) To turn off SCR
B) To reduce harmonics
C) To limit current
D) To change polarity
Answer: A) To turn off SCR
11. The maximum efficiency of a class-E inverter is achieved when
A) Load is purely resistive
B) Load is inductive
C) Load is capacitive
D) Resonance condition is met
Answer: D) Resonance condition is met
12. In a single-phase inverter, if the frequency is doubled, the output RMS voltage
A) Doubles
B) Halves
C) Remains same
D) Becomes zero
Answer: C) Remains same
13. The main control variable in PWM inverter is
A) Amplitude
B) Frequency
C) Pulse width
D) Phase angle
Answer: C) Pulse width
14. The main advantage of sinusoidal PWM is
A) Reduced lower order harmonics
B) Increased losses
C) Simplicity
D) High voltage stress
Answer: A) Reduced lower order harmonics
15. The function of snubber circuit across SCR is
A) Limit di/dt
B) Limit dv/dt
C) Reduce heat
D) Increase conduction time
Answer: B) Limit dv/dt
16. The main cause of thermal runaway in BJT is
A) High current
B) Negative temperature coefficient
C) Positive temperature coefficient
D) Overvoltage
Answer: C) Positive temperature coefficient
17. In MOSFET, conduction losses are due to
A) Rds(on)
B) Leakage current
C) Switching loss
D) Thermal loss
Answer: A) Rds(on)
18. In IGBT, tail current occurs due to
A) Stored charge in drift region
B) Gate resistance
C) Inductive load
D) Temperature variation
Answer: A) Stored charge in drift region
19. GTO can be turned off by
A) Reverse voltage
B) Negative gate current
C) Positive gate current
D) Line commutation
Answer: B) Negative gate current
20. The voltage across a thyristor during turn-off time is
A) Zero
B) Forward
C) Reverse
D) Alternating
Answer: C) Reverse
21. In AC voltage controllers, firing angle controls
A) RMS output voltage
B) Frequency
C) Power factor
D) Current direction
Answer: A) RMS output voltage
22. The power factor of a single-phase full converter is low because
A) Supply current is lagging
B) Supply voltage is low
C) SCRs operate at high frequency
D) Reactive load
Answer: A) Supply current is lagging
23. The main advantage of a current source inverter (CSI) is
A) Constant current output
B) Constant voltage output
C) Low cost
D) Simple commutation
Answer: A) Constant current output
24. The speed of a DC motor in a chopper drive is controlled by
A) Duty cycle
B) Supply voltage
C) Armature resistance
D) Field current
Answer: A) Duty cycle
25. In a dual converter, circulating current occurs due to
A) Difference in average voltages
B) Phase shift
C) Inductive load
D) Overlap angle
Answer: A) Difference in average voltages
26. In a single-phase AC regulator, if α = 90°, RMS output voltage is
A) Maximum
B) Zero
C) Half
D) 70% of input
Answer: B) Zero
27. The converter operating in inversion mode is
A) α < 90°
B) α = 90°
C) α > 90°
D) α = 0°
Answer: C) α > 90°
28. The control circuit of SCR provides
A) Proper gate pulse
B) DC supply
C) Commutation voltage
D) Output smoothing
Answer: A) Proper gate pulse
29. The duty cycle (D) in a chopper is defined as
A) Ton / (Ton + Toff)
B) Toff / Ton
C) Toff / T
D) 1 / T
Answer: A) Ton / (Ton + Toff)
30. The main reason for using PWM techniques is
A) Voltage regulation
B) Harmonic reduction
C) Cost reduction
D) Thermal management
Answer: B) Harmonic reduction
31. A TRIAC can conduct current in
A) One direction
B) Both directions
C) Only negative direction
D) Depends on firing
Answer: B) Both directions
32. The holding current of an SCR is
A) Greater than latching current
B) Equal to latching current
C) Less than latching current
D) Independent of latching current
Answer: C) Less than latching current
33. In a cycloconverter, output frequency is always
A) Higher than input
B) Equal to input
C) Lower than input
D) Unrelated
Answer: C) Lower than input
34. The main advantage of a voltage source inverter over current source inverter is
A) High efficiency
B) Low cost
C) Better voltage control
D) Simplicity
Answer: C) Better voltage control
35. In a DC chopper, ripple current decreases with
A) Increase in inductance
B) Decrease in frequency
C) Increase in load resistance
D) Increase in duty ratio
Answer: A) Increase in inductance
36. The best device for high-frequency low-power switching is
A) SCR
B) BJT
C) MOSFET
D) GTO
Answer: C) MOSFET
37. The dv/dt rating of an SCR indicates its
A) Voltage blocking ability
B) Turn-on capability
C) Turn-off capability
D) Sensitivity to transient
Answer: D) Sensitivity to transient
38. In an inverter, dead-time is introduced to
A) Avoid short circuit
B) Increase voltage
C) Improve waveform
D) Reduce switching losses
Answer: A) Avoid short circuit
39. A single-phase cycloconverter is generally used for
A) High frequency
B) Low frequency
C) Constant frequency
D) Variable voltage
Answer: B) Low frequency
40. The main limitation of SCR is
A) Cannot turn off by gate
B) Cannot handle high current
C) High on-state loss
D) High cost
Answer: A) Cannot turn off by gate
No comments:
Post a Comment