Power Semiconductor Devices MCQs

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1. What is the main advantage of a switching power supply compared to a linear power supply?
A) Higher efficiency
B) Lower cost
C) Smaller size
D) Lower electromagnetic interference
Answer: A) Higher efficiency

2. Which component in a switching power supply is responsible for converting DC voltage to high-frequency AC voltage?
A) Transformer
B) Diode
C) Capacitor
D) Inductor
Answer: A) Transformer

3. The duty cycle of a switching power supply refers to:
A) The ratio of on-time to total period
B) The maximum current it can supply
C) The frequency of the switching waveform
D) The efficiency of the power conversion
Answer: A) The ratio of on-time to total period

4. Which topology is commonly used in low-power switching power supplies due to its simplicity?
A) Flyback
B) Push-pull
C) Forward
D) Half-bridge
Answer: A) Flyback

5. The term “ripple voltage” in a switching power supply refers to:
A) The AC component superimposed on the DC output
B) The voltage drop across the diode
C) The voltage loss in the inductor
D) The voltage across the switching transistor
Answer: A) The AC component superimposed on the DC output

6. Which parameter is crucial for determining the maximum current output of a switching power supply?
A) Input voltage range
B) Output voltage regulation
C) Output capacitance
D) Power transistor rating
Answer: D) Power transistor rating

7. In a forward converter topology, which component is used to store energy during the switching cycle?
A) Transformer
B) Diode
C) Capacitor
D) Inductor
Answer: D) Inductor

8. The purpose of the snubber circuit in a switching power supply is to:
A) Filter out high-frequency noise
B) Protect the transformer from overcurrent
C) Prevent voltage spikes
D) Increase efficiency
Answer: C) Prevent voltage spikes

9. Which type of switching power supply topology typically provides galvanic isolation between input and output?
A) Buck
B) Boost
C) Flyback
D) SEPIC
Answer: C) Flyback

10. Which control method is commonly used in modern switching power supplies to regulate output voltage?
A) Pulse-width modulation (PWM)
B) Phase-locked loop (PLL)
C) Frequency modulation (FM)
D) Amplitude modulation (AM)
Answer: A) Pulse-width modulation (PWM)

11. The switching frequency of a power supply is primarily determined by:
A) The load current
B) The input voltage
C) The power transistor
D) The controller IC
Answer: D) The controller IC

12. A switching power supply operates in discontinuous conduction mode (DCM) when:
A) The load current is very high
B) The output voltage is regulated
C) The inductor current drops to zero during the switching cycle
D) The switching transistor is turned off
Answer: C) The inductor current drops to zero during the switching cycle

13. Which parameter is NOT typically a disadvantage of switching power supplies?
A) EMI generation
B) Complexity
C) Ripple voltage
D) High cost
Answer: D) High cost

14. The main advantage of a flyback converter over a forward converter is:
A) Higher efficiency
B) Lower EMI
C) Simpler design
D) Multiple outputs
Answer: D) Multiple outputs

15. Which component is essential for energy storage and transfer in a boost converter?
A) Transformer
B) Diode
C) Capacitor
D) Inductor
Answer: D) Inductor

16. The efficiency of a switching power supply is calculated as:
A) (Output power – Input power) / Output power
B) (Output power + Input power) / Input power
C) (Output power / Input power) × 100%
D) (Input power / Output power) × 100%
Answer: C) (Output power / Input power) × 100%

17. Which topology is known for its bidirectional capability, making it suitable for applications requiring both step-up and step-down conversions?
A) Flyback
B) SEPIC
C) Buck-boost
D) Push-pull
Answer: C) Buck-boost

18. In a half-bridge converter, how many switches are used?
A) One
B) Two
C) Three
D) Four
Answer: B) Two

19. The term “soft start” in switching power supplies refers to:
A) Gradually ramping up the output voltage
B) Reducing the switching frequency
C) Adding a snubber circuit
D) Improving the efficiency at low loads
Answer: A) Gradually ramping up the output voltage

20. Which type of control loop is used to regulate the output voltage of a switching power supply?
A) Current feedback
B) Voltage feedback
C) Phase-locked loop
D) Frequency modulation
Answer: B) Voltage feedback

21. The main advantage of a resonant converter compared to traditional switching converters is:
A) Higher efficiency
B) Lower output ripple
C) Smaller size
D) Lower cost
Answer: A) Higher efficiency

22. Which type of switching power supply is typically used in battery-operated devices to step up or step down the voltage?
A) Buck
B) Boost
C) Flyback
D) Push-pull
Answer: B) Boost

23. The primary purpose of the input filter in a switching power supply is to:
A) Prevent output voltage spikes
B) Reduce conducted EMI
C) Improve power factor
D) Stabilize the output voltage
Answer: B) Reduce conducted EMI

24. Which parameter is critical in determining the maximum output power of a switching power supply?
A) Input voltage range
B) Output voltage regulation
C) Output current rating
D) Switching frequency
Answer: C) Output current rating

25. Which component is used to rectify the AC output of the transformer in a flyback converter?
A) Diode
B) Capacitor
C) Inductor
D) Transformer
Answer: A) Diode

26. Which topology allows for seamless transition between step-up and step-down conversions without a change in polarity?
A) Buck
B) Boost
C) Buck-boost
D) Flyback
Answer: C) Buck-boost

27. The term “load regulation” in a switching power supply refers to:
A) The ability to maintain constant output voltage despite changes in load
B) Minimizing electromagnetic interference
C) Maximizing efficiency at full load
D) Adjusting the duty cycle of the switching waveform
Answer: A) The ability to maintain constant output voltage despite changes in load

28. Which parameter indicates the ability of a switching power supply to maintain a constant output voltage with varying input voltage?
A) Line regulation
B) Load regulation
C) Efficiency
D) Ripple voltage
Answer: A) Line regulation

29. A buck-boost converter is capable of:
A) Stepping up voltage only
B) Stepping down voltage only
C) Both stepping up and stepping down voltage
D) Generating multiple output voltages simultaneously
Answer: C) Both stepping up and stepping down voltage

30. Which control method is used in resonant converters to achieve high efficiency?
A) PWM
B) Phase control
C) Zero voltage switching (ZVS)
D) Hysteresis control
Answer: C) Zero voltage switching (ZVS)

31. The term “power factor correction (PFC)” in switching power supplies refers to:
A) Maximizing the power output
B) Reducing harmonic distortion in the input current
C) Improving efficiency at light loads
D) Stabilizing the output voltage
Answer: B) Reducing harmonic distortion in the input current

32. Which topology is preferred in applications requiring high power output due to its ability to handle large currents?
A) Buck
B) Boost
C) Full-bridge
D) Flyback
Answer: C) Full-bridge

33. Which component in a switching power supply stores energy during the on-time of the switching transistor?
A) Transformer
B) Capacitor
C) Inductor
D) Diode
Answer: C) Inductor

34. The primary advantage of a phase-shifted full-bridge converter is:
A) Higher efficiency
B) Lower EMI
C) Better thermal management
D) Simpler control circuitry
Answer: B) Lower EMI

35. Which type of feedback is essential for stable operation in a switching power supply?
A) Voltage feedback
B) Current feedback
C) Phase feedback
D) Frequency feedback
Answer: A) Voltage feedback

36. The term “duty cycle” in a switching power supply refers to:
A) The percentage of time the switching transistor is on
B) The ratio of inductance to capacitance
C) The frequency of the switching waveform
D) The efficiency of power conversion
Answer: A) The percentage of time the switching transistor is on

37. In a SEPIC converter, the primary benefit is:
A) Step-up conversion only
B) Step-down conversion only
C) Step-up and step-down conversion with non-inverted output
D) High-frequency operation
Answer: C) Step-up and step-down conversion with non-inverted output

38. The output capacitor in a switching power supply is primarily used to:
A) Filter high-frequency noise
B) Store energy during the switching cycle
C) Regulate the switching frequency
D) Provide isolation between input and output
Answer: A) Filter high-frequency noise

39. In a switching power supply, what is the main function of the control loop?
A) To manage the input voltage
B) To regulate the output voltage
C) To filter out noise
D) To control the switching frequency
Answer: B) To regulate the output voltage

40. A common disadvantage of switching power supplies compared to linear power supplies is:
A) Lower efficiency
B) Higher cost
C) More complex design
D) Larger size
Answer: C) More complex design

41. The term “EMI” in the context of switching power supplies stands for:
A) Electronic Magnetic Interference
B) Electromagnetic Interference
C) Electronic Management Interface
D) Electrical Magnetic Insulation
Answer: B) Electromagnetic Interference

42. Which control technique helps to improve the transient response of a switching power supply?
A) Pulse-width modulation
B) Digital signal processing
C) Voltage-mode control
D) Current-mode control
Answer: D) Current-mode control

43. In a resonant converter, the term “resonant” refers to:
A) The use of a high switching frequency
B) The operation at a specific resonant frequency
C) The use of a transformer for isolation
D) The integration of multiple control loops
Answer: B) The operation at a specific resonant frequency

44. Which component in a switching power supply is most affected by thermal stress?
A) Diode
B) Capacitor
C) Transformer
D) Inductor
Answer: A) Diode

45. The primary purpose of a rectifier in a switching power supply is to:
A) Convert AC voltage to DC voltage
B) Filter out high-frequency noise
C) Store energy during the switching cycle
D) Regulate the output voltage
Answer: A) Convert AC voltage to DC voltage

46. Which control method is commonly used for high-precision applications in switching power supplies?
A) Voltage-mode control
B) Current-mode control
C) Digital control
D) Analog feedback
Answer: C) Digital control

47. The main advantage of using a full-bridge converter is:
A) Simplicity in design
B) High efficiency and power capability
C) Low EMI
D) Smaller size
Answer: B) High efficiency and power capability

48. A critical factor affecting the stability of a switching power supply is:
A) Switching frequency
B) Input voltage
C) Load current
D) Control loop bandwidth
Answer: D) Control loop bandwidth

49. In a boost converter, the energy is stored in which component during the switching cycle?
A) Capacitor
B) Transformer
C) Inductor
D) Diode
Answer: C) Inductor

50. Which topology is characterized by the use of a transformer to provide isolation and voltage conversion in a single stage?
A) Buck
B) Flyback
C) Boost
D) Forward
Answer: B) Flyback

51. The primary function of the output filter in a switching power supply is to:
A) Smooth out the output voltage
B) Protect the power transistor
C) Increase the efficiency
D) Regulate the input current
Answer: A) Smooth out the output voltage

52. Which type of converter topology would be ideal for a scenario requiring both high power density and isolation?
A) Buck
B) Boost
C) Flyback
D) Buck-boost
Answer: C) Flyback

53. The main disadvantage of using a linear power supply compared to a switching power supply is:
A) Higher efficiency
B) Smaller size
C) Lower cost
D) Lower efficiency
Answer: D) Lower efficiency

54. In a switching power supply, “duty cycle” directly influences:
A) The efficiency of power conversion
B) The switching frequency
C) The output voltage
D) The input voltage
Answer: C) The output voltage

55. The term “peak current limiting” in a switching power supply refers to:
A) Limiting the maximum allowable input current
B) Controlling the peak value of the switching transistor current
C) Reducing the output voltage ripple
D) Minimizing the switching losses
Answer: B) Controlling the peak value of the switching transistor current

56. The purpose of a current sense resistor in a switching power supply is to:
A) Measure the output voltage
B) Monitor the load current
C) Filter high-frequency noise
D) Regulate the switching frequency
Answer: B) Monitor the load current

57. Which type of converter is used when precise voltage regulation is required in low-power applications?
A) Flyback
B) Buck
C) Boost
D) SEPIC
Answer: B) Buck

58. In a switched-mode power supply, what is the role of a “feedback loop”?
A) To provide isolation between input and output
B) To regulate the output voltage or current
C) To filter out high-frequency noise
D) To convert AC voltage to DC voltage
Answer: B) To regulate the output voltage or current

59. Which type of switching power supply topology is known for its ability to provide multiple outputs with high efficiency?
A) Flyback
B) Full-bridge
C) Buck-boost
D) Forward
Answer: A) Flyback

60. The term “dead time” in a switching power supply refers to:
A) The time when no switching occurs
B) The time between switching transitions
C) The time required for the power supply to stabilize
D) The time the output is disconnected
Answer: B) The time between switching transitions

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