Power Electronics Trivia Quiz

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| By Kingfaisalrahman
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Kingfaisalrahman
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Quizzes Created: 1 | Total Attempts: 472
Questions: 20 | Attempts: 472

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Power Electronics Quizzes & Trivia

Questions and Answers
  • 1. 

    Modern ac-dc converters employ self commutated devices like GTOs of IGBTs instead of thyristors inorder to achieve

    • A.

      Low reactive power loading on the source

    • B.

      Better efficiency in conversion

    • C.

      Low switching frequency operation of devices

    • D.

      Cost reduction in converter realization

    Correct Answer
    A. Low reactive power loading on the source
    Explanation
    Modern ac-dc converters employ self commutated devices like GTOs or IGBTs instead of thyristors in order to achieve low reactive power loading on the source. This is because self commutated devices have the ability to control the power flow and reduce reactive power consumption, resulting in a more efficient conversion process. By reducing the reactive power loading on the source, the converter can operate more efficiently and effectively, leading to improved overall performance.

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  • 2. 

    Power electronic device with poor turn-off gain is

    • A.

      A symmetrical thyristor

    • B.

      A conventioanal thyristor

    • C.

      Power bipolar junction transistor

    • D.

      Gate turn-off thyristor

    Correct Answer
    D. Gate turn-off thyristor
    Explanation
    A gate turn-off thyristor (GTO) is a power electronic device that has poor turn-off gain. This means that it is not very efficient at turning off the current flowing through it when the gate signal is applied. GTOs are commonly used in high power applications where fast switching is required. They have a higher voltage rating and lower on-state voltage drop compared to conventional thyristors, making them more suitable for certain applications. However, their poor turn-off gain means that they are not as efficient at turning off the current, which can result in higher power losses and reduced overall performance.

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  • 3. 

    In a 3-phase semi-converter, for firing angle less than or equal to 60degrees, free wheeling diode conducts for 

    • A.

      30 degrees

    • B.

      60 degrees

    • C.

      90 degrees

    • D.

      0 degrees

    Correct Answer
    D. 0 degrees
    Explanation
    In a 3-phase semi-converter, the free wheeling diode conducts when the firing angle is less than or equal to 60 degrees. This means that the diode conducts for the entire 360 degrees of the input waveform, including the zero degrees phase angle. Therefore, the answer is 0 degrees.

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  • 4. 

    In a 1-phase full converter, if load current is I and ripple free, than average thyristor current is

    • A.

      1/2*I

    • B.

      1/3*I

    • C.

      1/4*I

    • D.

      I

    Correct Answer
    A. 1/2*I
    Explanation
    In a 1-phase full converter, the average thyristor current can be determined by considering the conduction intervals of the thyristors. In this case, since the load current is ripple-free, each thyristor conducts for half of the input cycle. Therefore, the average thyristor current is half of the load current (1/2 * I).

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  • 5. 

    When an UJT is used for triggering an SCR, the waveshape of the voltage obtained from UJT  circuit is a

    • A.

      Sine wave

    • B.

      Saw-tooth wave

    • C.

      Trapezoidal wave

    • D.

      Square wave

    Correct Answer
    B. Saw-tooth wave
    Explanation
    When an UJT (Unijunction Transistor) is used for triggering an SCR (Silicon Controlled Rectifier), the waveshape of the voltage obtained from the UJT circuit is a saw-tooth wave. A saw-tooth wave is characterized by a linear rise in voltage followed by a sudden drop to its original value, resembling the teeth of a saw. This waveshape is suitable for triggering the SCR as it provides the necessary voltage variation to turn on the SCR at the desired timing.

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  • 6. 

    Which one of the following is used as the main switching element in a switched mode power supply operating in 20khz to 100khz range?

    • A.

      Thyristor

    • B.

      MOSFET

    • C.

      TRIAC

    • D.

      UJT

    Correct Answer
    B. MOSFET
    Explanation
    A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as the main switching element in a switched mode power supply operating in the 20kHz to 100kHz range. This is because MOSFETs have fast switching speeds, low on-resistance, and high efficiency, making them ideal for high-frequency applications like switched mode power supplies. Thyristors, TRIACs, and UJTs are not commonly used as switching elements in this frequency range, as they have different characteristics and are better suited for other types of circuits.

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  • 7. 

    Turn-on and Turn-off times of transistor depend on

    • A.

      Static characteristics

    • B.

      Junction capacitance

    • C.

      Current gain

    • D.

      None of these

    Correct Answer
    B. Junction capacitance
    Explanation
    The turn-on and turn-off times of a transistor are influenced by the junction capacitance. Junction capacitance refers to the capacitance between the different regions of a transistor, such as the base-emitter and base-collector junctions. During turn-on and turn-off, the junction capacitance affects the charging and discharging of these junctions, which in turn affects the time required for the transistor to switch between on and off states. Therefore, the junction capacitance directly impacts the turn-on and turn-off times of a transistor.

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  • 8. 

    IGBT is use for applications in 

    • A.

      Low power

    • B.

      Medium power

    • C.

      High power

    • D.

      None of these

    Correct Answer
    B. Medium power
    Explanation
    IGBT stands for Insulated Gate Bipolar Transistor. It is a type of power semiconductor device that combines the advantages of both MOSFET and bipolar junction transistor. IGBTs are commonly used in medium power applications due to their ability to handle moderate voltage and current levels. They are widely used in various applications such as motor drives, power supplies, renewable energy systems, and industrial automation. IGBTs offer high efficiency, fast switching speed, and low conduction losses, making them suitable for medium power applications.

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  • 9. 

    A 4-quadrant chopper cannot be operated as

    • A.

      1-quadrant chopper

    • B.

      Cyclo converter

    • C.

      Inverter

    • D.

      Bi-directional rectifier

    Correct Answer
    B. Cyclo converter
    Explanation
    A 4-quadrant chopper is a device that can control the direction and magnitude of power flow in both the positive and negative directions. It is capable of operating as a 1-quadrant chopper, inverter, and bi-directional rectifier. However, it cannot function as a cyclo converter. A cyclo converter is a device that converts AC power to a different frequency without changing its magnitude. Since a 4-quadrant chopper does not have the necessary circuitry to perform this conversion, it cannot be operated as a cyclo converter.

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  • 10. 

    Power diodes has characteristics of 

    • A.

      High power,high speed

    • B.

      Low power,low speed

    • C.

      Low power,high speed

    • D.

      High power,low speed

    Correct Answer
    D. High power,low speed
    Explanation
    Power diodes are designed to handle high levels of electrical power, making them suitable for applications that require high power capabilities. However, they have a slower switching speed compared to other diodes. This slower speed is due to their larger size and construction, which results in higher capacitance and longer recovery times. Therefore, power diodes are ideal for applications that prioritize power handling over speed, such as power supplies, rectifiers, and motor control circuits.

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  • 11. 

    The most suitable device for high frequency inversion in SMPS is

    • A.

      BJT

    • B.

      IGBT

    • C.

      MOSFET

    • D.

      GTO

    Correct Answer
    C. MOSFET
    Explanation
    MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is the most suitable device for high frequency inversion in Switch Mode Power Supplies (SMPS). This is because MOSFETs have fast switching speeds and low on-resistance, making them ideal for high frequency applications. They also have a higher efficiency and can handle higher power levels compared to other devices like BJT, IGBT, and GTO. Therefore, MOSFETs are commonly used in SMPS designs to efficiently convert and regulate power at high frequencies.

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  • 12. 

    Which of the following doesnot cause permanent damage of an SCR

    • A.

      High current

    • B.

      High rate of rise of current

    • C.

      High temperature rise

    • D.

      High rate of raise of voltage

    Correct Answer
    B. High rate of rise of current
    Explanation
    A high rate of rise of current does not cause permanent damage to an SCR. An SCR, or Silicon Controlled Rectifier, is a type of electronic switch that can handle high currents and voltages. However, it is sensitive to sudden changes in current and voltage. A high rate of rise of current refers to a rapid increase in the current flowing through the SCR. While this can cause temporary stress on the SCR, it does not cause permanent damage because the SCR is designed to handle high currents. On the other hand, high currents, high temperature rise, and high rate of rise of voltage can all potentially cause permanent damage to an SCR.

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  • 13. 

    A converter which can operate in both 3-phase and 6-pulse modes is a

    • A.

      1-phase full converter

    • B.

      3-phase half wave converter

    • C.

      3-phase semi converter

    • D.

      3-phase full converter

    Correct Answer
    C. 3-phase semi converter
    Explanation
    A 3-phase semi converter is a converter that can operate in both 3-phase and 6-pulse modes. In the 3-phase mode, it converts the input AC power into DC power using three thyristors. In the 6-pulse mode, it uses six thyristors to convert the input AC power into DC power. This flexibility allows the converter to adapt to different power requirements and provide efficient conversion in both modes.

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  • 14. 

    In d.c choppers per unit ripple is maximum when duty cycle alpha is

    • A.

      0.1

    • B.

      0.3

    • C.

      0.5

    • D.

      0.7

    Correct Answer
    C. 0.5
    Explanation
    The maximum ripple in a d.c. chopper occurs when the duty cycle alpha is 0.5. This is because at a duty cycle of 0.5, the chopper is switching on and off equally, resulting in a higher variation in the output voltage. When the duty cycle is less than 0.5, the chopper spends more time in the off state, resulting in a lower ripple. Similarly, when the duty cycle is greater than 0.5, the chopper spends more time in the on state, again resulting in a lower ripple. Therefore, the maximum ripple occurs at a duty cycle of 0.5.

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  • 15. 

    Which of the following devices should be used as a switch in a low power switched mode power supply(SMPS)

    • A.

      GTO

    • B.

      MOSFET

    • C.

      TRIAC

    • D.

      THYRISTOR

    Correct Answer
    B. MOSFET
    Explanation
    In a low power switched mode power supply (SMPS), a MOSFET should be used as a switch. MOSFETs are commonly used in SMPS due to their low on-resistance, fast switching speed, and high efficiency. They can handle high currents and voltages, making them suitable for switching applications. Additionally, MOSFETs have a low gate drive voltage requirement, which helps in reducing power losses and improving overall efficiency in low power SMPS designs.

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  • 16. 

    Inverters are used in

    • A.

      Induction heating

    • B.

      UPS

    • C.

      None of these

    • D.

      Both

    Correct Answer
    D. Both
    Explanation
    Inverters are used in both induction heating and UPS systems. In induction heating, inverters are used to convert DC power into high-frequency AC power, which is then used to heat conductive materials. In UPS systems, inverters are used to convert DC power from batteries into AC power, providing a backup power source during outages. Therefore, the correct answer is both.

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  • 17. 

    Commutation overlap in the phase controlled ac to dc converter is due to

    • A.

      Load inductance

    • B.

      Harmonic content of load current

    • C.

      Switching operator in the converter

    • D.

      Source inductance

    Correct Answer
    D. Source inductance
    Explanation
    The commutation overlap in the phase controlled ac to dc converter is due to the source inductance. The source inductance plays a crucial role in the converter as it helps in the smooth switching of the phase controlled converter. It helps in reducing the rate of change of current during the commutation process, thus preventing any overlap or interruption in the conversion process. Therefore, the presence of source inductance is necessary to ensure proper commutation in the phase controlled ac to dc converter.

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  • 18. 

    Cyclo converter can be considered as a.c-a.c converter with conversion of

    • A.

      1 stage

    • B.

      2 stage

    • C.

      3 stage

    • D.

      None of these

    Correct Answer
    A. 1 stage
    Explanation
    A cyclo converter is a type of AC-AC converter that converts the frequency of the input AC power. It is considered to have 1 stage because it directly converts the input AC power to the desired output AC power without any intermediate stages or additional components. In other words, it performs the conversion in a single step or stage, making it a 1-stage converter.

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  • 19. 

    In a step-down cyclo converter commutation required is

    • A.

      Natural

    • B.

      Forced

    • C.

      Depends on power

    • D.

      None of these

    Correct Answer
    A. Natural
    Explanation
    In a step-down cyclo converter, the commutation required is natural. This means that the commutation process occurs naturally without the need for any external control or intervention. The cyclo converter switches automatically based on the voltage and current conditions in the circuit. This natural commutation ensures smooth and efficient operation of the cyclo converter without the need for additional components or complex control systems.

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  • 20. 

    Triacs cannot be used in a.c voltage regulator for a

    • A.

      Resistive load

    • B.

      Back e.m.f load

    • C.

      Inductive load

    • D.

      Resistive inductive load

    Correct Answer
    C. Inductive load
    Explanation
    Triacs cannot be used in an a.c voltage regulator for an inductive load because inductive loads generate back e.m.f (electromotive force) when the current flowing through them changes. This back e.m.f can cause the triac to turn off prematurely, leading to unstable regulation of the voltage. Therefore, using a triac in an a.c voltage regulator for an inductive load would not provide reliable and accurate voltage regulation.

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