Fundamentals of Power Electronics

Multiple Choice Questions (MCQs)

1   Which of the following is the application of Power Electronics?
    (A)   Fan Regulator
    (B)   Temperature controller
    (C)   Cycloconverter
    (D)   All the above
2   Which of the following is not triggering device?
    (A)   UJT
    (B)   SCR
    (C)   DIAC
    (D)   SBS
3   Long form of SCR is
    (A)   Silicon Conversion Rectifier
    (B)   Silicon Controlled Rectifier
    (C)   Selenium Controlled Rectifier
    (D)   None of the above
4   Which of the following is not Power Controlled Rectifier?
    (A)   SCR
    (B)   TRIAC
    (C)   UJT
    (D)   LASCR
5   SCR is a…..
    (A)   Four Layer Three Terminal Device
    (B)   Three Layer Four Terminal Device
    (C)   Four Layer Four Terminal Device
    (D)   Four Layer Two Terminal Device
6   TRIAC is a
    (A)   Unidirectional device
    (B)   Bidirectional Device
    (C)   Sometime Bidirectional device
    (D)   Cannot say
7   Which of the following is not part of VI characteristics of SCR?
    (A)   Forward Blocking state
    (B)   Forward Conduction state
    (C)   Saturation State
    (D)   Reverse Blocking State
8   Which of the following holds true for relationship between Holding current and Latching Current?
    (A)   Holding Current > Latching current
    (B)   Holding Current < Latching current
    (C)   Holding Current = Latching current
    (D)   Holding Current <= Latching current
9   As value of gate current through SCR increases
    (A)   Value of breakover voltage decreases
    (B)   Value of breakover voltage increases
    (C)   Value of breakover voltage remains unchanged
    (D)   None of the above
10   On state voltage drop across SCR is approximately equals to
    (A)   10 volts
    (B)   100 volts
    (C)   0.1 volt
    (D)   1 volt
11   Following symbol represents…

    (A)   DIAC
    (B)   TRIAC
    (C)   SCR
    (D)   UJT
12   Which of the following is most widely used turn on methods of SCR?
    (A)   Gate Triggering
    (B)   Light Triggering
    (C)   Forward Voltage Triggering
    (D)   dv/dt Triggering
13   Which of the following Thyristor can be turned on by light triggering?
    (A)   SCR
    (B)   TRIAC
    (C)   DIAC
    (D)   LASCR
14   Two transistor analogy of SCR can be achieved by using
    (A)   Any two-transistor choice
    (B)   Two PNP transistor
    (C)   One PNP and One NPN transistor
    (D)   One FET and One MOSFET transistor
15   For Protecting SCR from over voltage which of the following protection technique is used
    (A)   Snubber Circuit
    (B)   Inductor is connected in series
    (C)   Fuse is connected in series
    (D)   Heat sink
16   Commutation is process of
    (A)   Turning On SCR
    (B)   Turning Off SCR
    (C)   Checking SCR
    (D)   Converting SCR into TRIAC
17   Which of the following is not Forced Commutation?
    (A)   Class A commutation
    (B)   Class C commutation
    (C)   Class E commutation
    (D)   Class F commutation
18   Class C commutation is also called as
    (A)   Auxiliary Commutation
    (B)   Resonant Commutation
    (C)   Self-Commutation
    (D)   Complimentary Commutation
19   Following diagram represents which type of commutation

    (A)   Auxiliary Commutation
    (B)   Resonant Commutation
    (C)   Self-Commutation
    (D)   Complimentary commutation
20   Following symbol represents which triggering device

    (A)   UJT
    (B)   PUT
    (C)   DIAC
    (D)   SBS
21   In Forward blocking state, Junctions
    (A)   J1 – Forward Bias, J2-Forward Bias, J3- Forward Bias
    (B)   J1 – Forward Bias, J2-Forward Bias, J3- Reverse Bias
    (C)   J1 – Reverse Bias, J2-Forward Bias, J3- Reverse Bias
    (D)   None of the above
22   Role of protection circuit is
    (A)   Protect load from excess current and voltages
    (B)   Protect Source from excess current and voltages
    (C)   Protect SCR (Thyristor) from excess current and voltages
    (D)   None of the above
23   UJT exhibits …………………… in its chart eristics
    (A)   Positive Resistance Region
    (B)   Negative Resistance Region
    (C)   Non Ohmic Region
    (D)   Conductive Region
24   Long form of PUT is
    (A)   Programmable Uni Junction Transistor
    (B)   Programmable Unique Junction Thyristor
    (C)   Pointed Unit Transistor
    (D)   None of the above
25   Pulse duration in UJT relaxation oscillator is controlled by using
    (A)   R and C combination
    (B)   Resistor Only
    (C)   Capacitor only
    (D)   By UJT
26   Which of the following is not Power Controlled Rectifier
    (A)   SCR
    (B)   TRIAC
    (C)   UJT
    (D)   LASCR
27   Following symbol represents which Power Semiconductor device
    (A)   SCR
    (B)   Transistor
    (C)   IGBT
    (D)   MOSFET
28   In case of controlled rectifiers, Average value of output voltage is high when firing angle is equals to ….
    (A)   0 degree
    (B)   45 degrees
    (C)   90 degrees
    (D)   180 degrees
29   In half wave-controlled rectifier, Conduction angle is maximum when…….
    (A)   Firing angle is minimum
    (B)   Firing angle is maximum
    (C)   Firing angle is equal to conduction angle
    (D)   Cannot say
30   In case of Controlled rectifier with RL load, Freewheeling diode is connected in
    (A)   Series with load
    (B)   Parallel with load
    (C)   Either series or parallel
    (D)   No need to connect freewheeling diode for RL load
31   Semi converter with RL load makes use of……….
    (A)   Four SCR
    (B)   Two SCR, Two PN junction Diode
    (C)   Four PN junction Diode
    (D)   Three SCR, One PN junction diode
32   Which of the following is the role of Freewheeling diode in controlled rectifiers
    (A)   It improves voltage waveform
    (B)   It increases average value of output voltage
    (C)   It maintains load current constant
    (D)   All the above
33   A single-phase half wave rectifier is used to supply power to load impedance 10-ohm form 230 V, 50 Hz AC supply at firing angle 30 degree, what is the average load voltage
    (A)   95.5
    (B)   96.6
    (C)   106.3
    (D)   86.4
34   Long form of SMPS is
    (A)   System Modulated Power Supply
    (B)   System Monitored Power Source
    (C)   Switch Mode Power Supply
    (D)   Switch Modulated Power system
35   Following block diagram represents which type of UPS
    (A)   Offline UPS
    (B)   Online UPS
    (C)   Main line UPS
    (D)   Secondary UPS
36   At which of the following UPS is not used
    (A)   For EPABX system
    (B)   For computer system
    (C)   Intensive care unit
    (D)   Induction Heating application
37   Output voltage waveform of Offline UPS is…
    (A)   Sinusoidal wave
    (B)   Quasi square wave
    (C)   Quasi Triangular wave
    (D)   Saw tooth wave
38   Following circuit diagram represents…
    (A)   Full wave-controlled Rectifier
    (B)   Half wave-controlled Rectifier
    (C)   Semi controlled Rectifier
    (D)   All the above
39   Following diagram represents…
    (A)   Full wave-controlled bridge rectifier
    (B)   Full wave midpoint converter
    (C)   Semi converter
    (D)   Half wave-controlled rectifier
40   Following diagram represent which circuit…
    (A)   Full wave-controlled Bridge converter with freewheeling diode
    (B)   Full wave-controlled midpoint converter
    (C)   Full wave-controlled midpoint converter with freewheeling diode
    (D)   Half wave-controlled converter with freewheeling diode
41   For Full wave controlled Mid-Point converter…
    (A)   Transducer is used
    (B)   Normal transformer is used
    (C)   No need of transformer
    (D)   Center tap transformer is used
42   Average value of output DC voltage for half wave-controlled rectifier is
    (A)   Lower than full wave-controlled rectifier
    (B)   Higher than full wave-controlled rectifier
    (C)   Average value is constant for all the configuration
    (D)   None of the above
43   Firing angle in case of power-controlled rectifier is
    (A)   It is angle at which firing pulse is applied to gate terminal
    (B)   It is angle for which SCR is in conducting state
    (C)   It is angle for which SCR is in off condition
    (D)   It is the angle which is always contact
44   Conduction in case of power-controlled rectifier is
    (A)   It is angle at which firing pulse is applied to gate terminal
    (B)   It is angle for which SCR is in conducting state
    (C)   It is angle for which SCR is in off condition
    (D)   It is the angle which is always contact
45   Controlled rectifiers can be designed with the help of
    (A)   SCR’s only
    (B)   Diode’s only
    (C)   Transistor only
    (D)   MOSFET only
46   Following circuit diagram represents
    (A)   Symmetrical Semi converter
    (B)   Asymmetrical Semi converter
    (C)   Full wave-controlled converter
    (D)   Invalid circuit
47   Following waveform represents…
    (A)   Full wave-controlled convertor
    (B)   Half wave-controlled convertor
    (C)   Semi convertor
    (D)   None of the above
48   Following circuits represents.

    (A)   Fan Speed Regulator
    (B)   Battery charger
    (C)   Uninterrupted power supply
    (D)   Switch Mode power supply
49   Following diagram represents…
    (A)   UPS
    (B)   SMPS
    (C)   Battery charger
    (D)   Motor speed regulator
50   Which of the following application of UPS
    (A)   It regulates load voltage when main voltage fluctuates or OFF
    (B)   It supplies a pure, harmonic free signal to the load
    (C)   It suppresses the spikes and provides constant DC voltage
    (D)   All the above
51   In Forward blocking state, Junctions
    (A)   J1 – Forward Bias, J2-Forward Bias, J3- Forward Bias
    (B)   J1 – Forward Bias, J2-Forward Bias, J3- Reverse Bias
    (C)   J1 – Forward Bias, J2-Reverse Bias, J3- Forward Bias
    (D)   J1 – Reverse Bias, J2-Forward Bias, J3- Reverse Bias

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