# Power Electronics Test Questions - Set - 2

1)   An ideal diode is

a. Unidirectional
b. Bidirectional
c. Fixed voltage polarity
d. Only (a) and (c)
 Answer  Explanation  Related Ques ANSWER: Only (a) and (c) Explanation: No explanation is available for this question!

2)   Bidirectional semiconductor device is

a. Diode
b. BJT
c. SCR
d. TRIAC
 Answer  Explanation  Related Ques ANSWER: TRIAC Explanation: No explanation is available for this question!

3)   With gate open, the maximum anode current at which SCR is turned off from ON condition is called

a. breakdown voltage
b. peak reverse voltage
c. holding current
d. latching current
 Answer  Explanation  Related Ques ANSWER: holding current Explanation: No explanation is available for this question!

4)   The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known as

a. both as forward characteristics
b. both as reverse characteristics
c. former as forward characteristics and later as reverse characteristics
d. former as reverse characteristics and later as forward characteristics
 Answer  Explanation  Related Ques ANSWER: former as forward characteristics and later as reverse characteristics Explanation: No explanation is available for this question!

5)   Form factor of a rectifier is the ratio of

a. Root mean square value of voltage and current to its peak value
b. Root mean square value of voltage and current to its average value
c. Average value of current and voltage to its root mean square value
d. Peak value of current and voltage to its root mean square value
 Answer  Explanation  Related Ques ANSWER: Root mean square value of voltage and current to its average value Explanation: No explanation is available for this question!

6)   Ripple factor is the ratio of

a. Rms value of the ac component of load voltage to the dc voltage
b. Average value of the ac component of load voltage to the peak value of voltage
c. Average value of the dc component of load voltage to the ac voltage
d. Peak value of the dc component of load voltage to the ac voltage
 Answer  Explanation  Related Ques ANSWER: Rms value of the ac component of load voltage to the dc voltage Explanation: No explanation is available for this question!

7)   Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of

a. AC input power to the transformer volt - amp rating required by secondary
b. AC input power to the transformer volt - amp rating required by primary
c. DC output power to the transformer volt - amp rating required by secondary
d. DC output power to the transformer volt - amp rating required by primary
 Answer  Explanation  Related Ques ANSWER: DC output power to the transformer volt - amp rating required by secondary Explanation: No explanation is available for this question!

8)   In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes

a. Positive
b. Negative
c. Zero
d. None of these
 Answer  Explanation  Related Ques ANSWER: Positive Explanation: No explanation is available for this question!

9)   If the firing angle becomes negative, then the rectifier begins to work as

a. A rectifier
b. An inverter
c. A chopper
d. A regulator
 Answer  Explanation  Related Ques ANSWER: An inverter Explanation: No explanation is available for this question!

10)   The Graetz bridge makes excellent use of

a. Current transformer
b. Potential transformer
c. Power transformer
d. SCR
 Answer  Explanation  Related Ques ANSWER: Power transformer Explanation: No explanation is available for this question!

11)   DIAC and TRIAC both are semiconductors devices and conduct in

a. DIAC conducts in forward direction and TRIAC conducts in reverse direction
b. Both conducts in forward direction
c. Both conducts in reverse direction
d. Both conducts in either direction
 Answer  Explanation  Related Ques ANSWER: Both conducts in either direction Explanation: No explanation is available for this question!

12)   A TRIAC can be turned on with

a. Positive voltage at the gate terminal
b. Negative voltage at the gate terminal
c. Either (a) or (b)
d. None of these
 Answer  Explanation  Related Ques ANSWER: Either (a) or (b) Explanation: No explanation is available for this question!

13)   The phase angle of gate signal in TRIAC can be shifted by using

a. A capacitor
b. A variable resistor
c. An inductor
d. Only (a) and (b)
 Answer  Explanation  Related Ques ANSWER: Only (a) and (b) Explanation: No explanation is available for this question!

14)   The ac voltage controller can be used for

a. Lighting and heating control
b. On - line transformer tap changing
c. Soft starting
d. All of these
 Answer  Explanation  Related Ques ANSWER: All of these Explanation: No explanation is available for this question!

15)   An RC snubber network used in BJT

a. Divert the collector current during turn - off
b. Improves the reverse bias safe operating area
c. Dissipates a fair amount of switching power
d. All of these
 Answer  Explanation  Related Ques ANSWER: All of these Explanation: No explanation is available for this question!

16)   A MOSFET, for its conduction uses

a. Only minority carriers
b. Only majority carriers
c. Both minority and majority carriers
d. None of these
 Answer  Explanation  Related Ques ANSWER: Only majority carriers Explanation: No explanation is available for this question!

17)   MOSFET stands for

a. Metal - oxide semiconductor field effect transistor
b. Molybdenum - oxide semiconductor field effect transistor
c. Metal - oxide silicon field effect transistor
d. Metal - oxide semiconductor field effect transmitter
 Answer  Explanation  Related Ques ANSWER: Metal - oxide semiconductor field effect transistor Explanation: No explanation is available for this question!

18)   In a push - pull converter, the filter capacitor can be obtained as

a. Cmin = V / ( Vr L f2 )
b. Cmin= ( 1 – D ) V / ( Vr L f2 )
c. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )
d. Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 )
 Answer  Explanation  Related Ques ANSWER: Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 ) Explanation: No explanation is available for this question!

19)   In a flyback converter, the inductor of the buck-boost converter has been replaced by a

a. Flyback capacitor
b. Flyback resistor
c. Flyback transformer
d. Flyback transistor
 Answer  Explanation  Related Ques ANSWER: Flyback transformer Explanation: No explanation is available for this question!

20)   Advantages of Cuk converter is / are

a. Large number of reactive component
b. Low stress on switch
c. Low stress on capacitor
d. None of these
 Answer  Explanation  Related Ques ANSWER: None of these Explanation: No explanation is available for this question!

21)   The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of

a. High dv / dt, low di / dt
b. Low dv / dt, low di / dt
c. Low dv / dt, high di / dt
d. High dv / dt, high di / dt
 Answer  Explanation  Related Ques ANSWER: High dv / dt, high di / dt Explanation: No explanation is available for this question!

22)   If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as

a. Motoring mode operation
b. Braking mode operation
c. Regenerative mode operation
d. None of these
 Answer  Explanation  Related Ques ANSWER: Regenerative mode operation Explanation: No explanation is available for this question!

23)   A combination of synchronized leading edge and trailing edge modulation has also been used to control a

a. Boost single - phase power factor converter
b. A buck dc - dc converter to reduce ripple in the intermediate dc bus capacitor
c. Both (a) and (b)
d. None f these
 Answer  Explanation  Related Ques ANSWER: Both (a) and (b) Explanation: No explanation is available for this question!

24)   Regulator sampling PWM is usually used in

a. High power inverters
b. Rectifiers
c. Low power inverters
d. Only (a) and (b)
 Answer  Explanation  Related Ques ANSWER: Only (a) and (b) Explanation: No explanation is available for this question!

25)   In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be

a. Multiple of two
b. Odd multiple of three
c. Odd multiple of five
d. Odd multiple of seven
 Answer  Explanation  Related Ques ANSWER: Odd multiple of three Explanation: No explanation is available for this question!

26)   In square wave operation mode of 3 phase VSI, the VSI

a. Can control the load voltage
b. Cannot control the load voltage
c. Cannot control the load voltage except by means of dc link voltage
d. Cannot control the load voltage except by means of dc link current
 Answer  Explanation  Related Ques ANSWER: Cannot control the load voltage except by means of dc link voltage Explanation: No explanation is available for this question!

27)   For commutation in three phase PAC, normally balanced three phase voltages  VR, VY and VB are connected to the three legs of the converter via

a. Three inductances
b. Three capacitances
c. Three resistance
d. Three transistors
 Answer  Explanation  Related Ques ANSWER: Three inductances Explanation: No explanation is available for this question!

28)   If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered

a. 120 degree after the zero crossing of the corresponding line voltages
b. 60 degree after the zero crossing of the corresponding line voltages
c. 120 degree before the zero crossing of the corresponding line voltages
d. 60 degree before the zero crossing of the corresponding line voltages
 Answer  Explanation  Related Ques ANSWER: 60 degree after the zero crossing of the corresponding line voltages Explanation: No explanation is available for this question!

29)   The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known as

a. Susceptibility
b. Emission
c. Interference
d. Electromagnetic compatibility
 Answer  Explanation  Related Ques ANSWER: Electromagnetic compatibility Explanation: No explanation is available for this question!

30)   The opposite of susceptibility is

a. Immunity
b. Emission
c. Interference
d. Electromagnetic compatibility
 Answer  Explanation  Related Ques ANSWER: Immunity Explanation: No explanation is available for this question!

31)   The output current in PWM DC - DC converters is equal to

a. Average value of the output inductor current
b. Product of an average inductor current and a function of duty ratio
c. Either (a) or (b)
d. None of these
 Answer  Explanation  Related Ques ANSWER: Either (a) or (b) Explanation: No explanation is available for this question!

32)   A step - down choppers can be used in

a. Electric traction
b. Electric vehicles
c. Machine tools
d. All of these
 Answer  Explanation  Related Ques ANSWER: All of these Explanation: No explanation is available for this question!

33)   In a lossless inverter, the average power absorbed in one period by the load must be

a. Equal to the average power supplied by the dc source
b. Greater than the average power supplied by the dc source
c. Lesser than the average power supplied by the dc source
d. Equal to the average power supplied by the ac source
 Answer  Explanation  Related Ques ANSWER: Equal to the average power supplied by the dc source Explanation: No explanation is available for this question!

34)   In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that

a. Top switch of each leg is on at any instant
b. Bottom switch of each leg is on at any instant
c. Either (a) or (b)
d. None of these
 Answer  Explanation  Related Ques ANSWER: Either (a) or (b) Explanation: No explanation is available for this question!

35)   In the SPWM, the modulating signal is

a. Square
b. Sinusoidal
c. Triangular
d. Saw - tooth
 Answer  Explanation  Related Ques ANSWER: Sinusoidal Explanation: No explanation is available for this question!

36)   The transfer function of PWM is generally developed in

a. Time domain
b. Frequency domain
c. Either (a) or (b)
d. None of these
 Answer  Explanation  Related Ques ANSWER: Either (a) or (b) Explanation: No explanation is available for this question!

37)   In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a

a. Linear function
b. Non linear function
c. Constant function
d. None of these
 Answer  Explanation  Related Ques ANSWER: None of these Explanation: No explanation is available for this question!

38)   In variable frequency, PWM gain

a. Phase lead helps to increase the phase margin of the control loop
b. Phase lag helps to increase the phase margin of the control loop
c. Phase lead helps to decrease the phase margin of the control loop
d. Phase lag helps to decrease the phase margin of the control loop
 Answer  Explanation  Related Ques ANSWER: Phase lead helps to increase the phase margin of the control loop Explanation: No explanation is available for this question!

39)   A carrier based PWM technique in CSI is composed of

a. A switching pulse generator and a shorting pulse generator
b. A shorting pulse distributor
c. A switching and shorting pulse combination
d. All of these
 Answer  Explanation  Related Ques ANSWER: All of these Explanation: No explanation is available for this question!

40)   In a square - wave operation of 3 phase CSIs, the power values are on for

a. 60 degree
b. 90 degree
c. 120 degree
d. 150 degree
 Answer  Explanation  Related Ques ANSWER: 120 degree Explanation: No explanation is available for this question!