POWER ELECTRONICS

Submitted by
sk mohammed wajuddin

Ques.1. A Silicon Controlled Rectifier (SCR) Is A

1. Unijunction Device
2. Device With Three Junction
3. Device With Four Junction
4. None Of The Above

Answer.2. Device With Three Junction

Ques.2. A Thyristor Is Basically

1. PNPN Device
2. A Combination Of Diac And Triac
3. A Set Of Scrs
4. A Set Of SCR, Diac And A Triac

Answer.1. PNPN Device

Ques.3. Which Semiconductor Power Device Out Of The Following, Is Not

A Current Triggering Device?
1. Thyristor
2. Triac
3. G.T.O
4. MOSFET

Answer.4. MOSFET
Ques.4. Which Of The Following Device Incorporates A Terminal For
Synchronizing Purposes?
1. Diac
2. Triac
3. SUS
4. None Of The Above

Answer.3. SUS

Ques.5. The Advantages Of SCS Over SCR Is

1. Slow Switching Time And Large VH
2. Slow Switching Time And Smallervh
3. Faster Switching Time And Smallervh
4. Faster Switching Time And Large VH

Answer.3. Faster Switching Time And Smallervh

Ques.6. A Thyristor Equivalent Of A Thyratron Tube Is A

1. Diac
2. Triac
3. Silicon Controlled Rectifier
4. None Of The Above
Hide Explanation
Answer.3. Silicon Controlled Rectifier

Ques.7. A Triac Is A
1. 2 Terminal Switch
2. 2 Terminal Bilateral Switch
3. 3 Terminal Bilateral Switch
4. 3 Terminal Bidirectional Switch

Answer.4. 3 Terminal Bidirectional Switch

Ques.8. The Fig. Below Represents A
1. Triac Thyristor
2. Diac Trigger
3. Diode Rectifier
4. None Of The Above
Hide Explanation
Answer.2. Diac Trigger

Ques.9. The Triple Frequency Of A Six-Phase Half Wave Rectifier For 220
V, 60 Hz Input Will Be
1. 2160 Hz
2. 720 Hz
3. 360 Hz
4. 60 Hz
Answer.3. 360 Hz

Ques.10. The Minimum Duration Of The Pulse In A Pulse Triggering System

For Thyristors Should Be At
1. 10 Μs
2. 10 Ms
3. 30 Ms
4. 1 Sec
Hide Explanation
Answer.1. 10 µs

Ques.11. The Inverter Can Be Classified As

1. Voltage Source Inverter
2. Current Source Inverter
3. Both 1 And 2
4. Power Inverter
Hide Explanation
Answer.3. Both 1 And 2

Ques.12. During Induction Heating, The Skin Depth Of Penetration Is

Proportional (F = Frequency) To
1. F
2. F2
3. 1/F
4. 1/√F
Hide Explanation
Answer.4. 1/√F
Explanation:-
Workpieces. High Frequencies Of Up To A Few Hundred Kilohertz Are
Used For Forging, Soldering, Hardening, And Annealing.

Ques.13. A Device That Cannot Be Triggered With Low Voltage Of Either

Polarity Is
1. Diac
2. Triac
3. SCS
4. All Of The Above
Hide Explanation
Answer.1. Diac
.

Ques.14. The Fig. Given Below Represents

 1. Silicon Controlled Rectifier
2. Field Effect Transistor
3. Photoemissive Diode
4. Tunnel Diode
Hide Explanation
Answer.1. Silicon Controlled Rectifier

Ques.15. In A Three-Phase Half-Wave Rectifier, Each Diode Conducts For A

Duration Of
1. 180°
2. 120°
3. 90°
4. 60°
Hide Explanation
Answer.2. 120°

Ques.16. Which Of The Following Finds Applications In Speed Control Of A

DC Motor?
1. FET
2. NPN Transistor
3. SCR
 4. None Of The Above
Hide Explanation
Answer.3. SCR
.

Ques.17. The Given Fig. Below Represents

1. Triac Thyristor
2. Diac Thyristor
3. Capacitive Diode
4. None Of The Above
Hide Explanation
Answer.1. Triac Thyristor
Explanation:-
The Triac Is A Three-Terminal Ac Switch That Is Triggered Into Conduction
When A Low-

Ques.18. The Ward-Leonard System Is Used For Controlling The Speed Of

1. DC Motors
2. Single Phase AC Motors
3. Three Phase Motors
4. Universal Motors
Hide Explanation
Answer.1. DC Motors
Explanation:
The Basic Principle Of The DC Variable Speed Drive Is That The Speed Of
A Separately Excited DC Motor Is Directly Proportional To The Voltage
Applied To The Armature Of The

Ques.19. A Device That Does Not Exhibit Negative Resistance

Characteristics Is
1. FET
2. UJT
3. Tunnel Diode
4. SCR
Hide Explanation
Answer 1. FET

Ques.20. A Triac
1. Conducts When Not Triggered
2. Conducts When Not Triggered In Both Direction
3. Conducts When Triggered In One Direction
4. None Of The Above
Hide Explanation
Answer. 2. Conducts When Not Triggered In Both Direction

Ques.21. For A Thyristor Shown Is

 1. All The 3 Junctions Are Forward Biased
2. J1, J2 Are Forward Biased And J3 Reversed Biased
3. J1 Is Forward Biased, J2, J3 Reversed Biased
4. J1, J2 Are Reversed Biased J3 Is Forward Biased
Hide Explanation
Answer. 2. J1, J2 Are Forward Biased And J3 Reversed Biased

Answer. 3. 3/√2
Explanation:

Ques.23. A Voltage Source 200 Sin314t Is Applied To A Thyristor

Controlled Halfwave Rectifier With A Resistive Load Of 50Ω. If The Firing
Angle Is 30° With Respect To Supply Voltage Waveform, The Average
Power In The Load Is
1. 90.6 Watts
2. 86.3 Watts
3. 60.8 Watts
4. 70.6 Watts
Hide Explanation
Answer.4. 70.6 Watts
Ques.24. RC Snubber Circuit Is Used To Limit The Rate Of
1. Rise Of Current In SCR
2. Rise Of Voltage Across SCR
3. Conduction Period
4. All Of The Above
Hide Explanation
Answer.2. Rise Of Voltage Across SCR
Explanation:

Ques.25. A Freewheeling Diode Is Connected Across An Inductive Load Is

1. To Restore Conduction Angle On Phase
2. To Avoid Negative Reversal Voltage Drop
3. To Reduce The PRV
4. All Of The Above
Hide Explanation
Answer.1. To Restore Conduction Angle On Phase

Ques.26. Equalizing Circuits Are Provided Across Each SCR In Series

Operation To Provide Uniform
1. Current Distribution
2. Voltage Distribution
3. Firing Of Scrs
4. All Of The Above
Hide Explanation
Answer.2. Voltage Distribution

Ques.27. For The High-Frequency Choppers, The Device That Is Preferred Is

1. TRIAC
2. Thyristor
3. Transistor
4. GTO
Hide Explanation
Answer 3. Transistor

Explanation:-
Ques.28. The Thyristor Is Turned -Off When The Anode Current Falls
Below_____
1. Forward Current
2. Latching Current
3. Holding Current
4. Breakover Current
Hide Explanation
Answer.3. Holding Current

Ques.29. In A Thyristor Circuit, The Angle Of Conduction Is Changed By

Changing______
1. Anode Voltage
2. Gate Current
3. Forward Current
4. Anode Current
Hide Explanation
Answer.2. Gate Current

Ques.30. A Fully Controlled Natural Commutated 3-Phase Bridge Rectifier Is

Operating With A Firing Angle Α = 30°. The Peak To Peak Voltage Ripple
Expressed As A Ratio Of The Peak Output Dc Voltage At The Output Of
The Converter Bridge Is
1. 0.5
2. √3/2
3. 2/√3
4. 1
Hide Explanation
Answer.1. 0.5

Ques.31. In AC Voltage Regulator, TRIACS Cannot Be Used For A

1. Back Emf Load
2. Resistive Load
 3. R-L Load
4. Inductive Load
Hide Explanation
Answer.4. Inductive Load

Ques.32. In A Thyristor
1. The Holding Current Is Greater Than Latching Current
2. The Two Current Are Equal
3. The Latching Current Is Greater The Holding Current
4. None Of The Above
Hide Explanation
Answer.3. The Latching Current Is Greater The Holding Current

Ques.33. The VI Characteristics Of UJT Is

1. Similar To CE With A Linear And Saturation Region
2. Similar To FET With A Linear And Pinch Off Region
3. Similar To Tunnel Diode In Some Respects
4. Similar To PN Junction Diode In Some Respects
Hide Explanation
Answer.3. Similar To Tunnel Diode In Some Respects

Ques.34. Chopper Control For DC Motor Provides Variation In

1. Input Voltage
2. Frequency
3. Current
4. None Of The Above
Hide Explanation
Answer.1. Input Voltage
Explanation:
Ques.35. In A Thyristor The Ratio Of Latching Current To Holding Current
Is
1. 0.5
2. 1
3. 2.7
4. 5
Hide Explanation
Answer.3. 2.7
Explanation:
The Typical Ratio Of Latching Current To Holding Current Lies In The
Range Of 2.5 To 3. Therefore, Only 2.7 Is The Nearest Option.
Hence, The Correct Option Is (3).

Ques.36. In A Thyristor, Dv/Dt Protection Is Achieved Through The Use Of

1. L Across Thyristor
2. RC Across Thyristor
3. R Across Thyristor
4. RL Across Thyristor
Hide Explanation
Answer.2. RC Across Thyristor
Explanation:
Thyristor Protection Or SCR Protection

Ques.37. In A Thyristor Di/Dt Protection Is Achieved Through The Use Of

1. L In Series With The Thyristor
2. R Across Thyristor
3. RC Across Thyristor
4. RL Across Thyristor
Hide Explanation
Answer.1. L In Series With The Thyristor
Explanation:

Ques.38. UJT When Used For Triggering An SCR, Has The Waveform
1. Sine Wave
2. Square Wave
3. Sawtooth Wave
4. Trapezoidal
Hide Explanation
Answer.3. Sawtooth Wave
Ques.39. A Resistor Connected Across The Gate And Cathode Of A
Thyristor Increase Its
1. Turn Off Time
2. Di/Dt Rating
3. Noise Immunity
4. Holding Current
Hide Explanation
Answer.4. Holding Current
Explanation:
 D3 Is Connected As Shown In The Figure To Block The Positive Gate
Current Coming From The Supply When The Device Is Homed Biased.

Ques.40. P-Side Emitter In UJT Is

1. Not Doped
2. Feebly Doped
3. Heavily Doped
4. Moderately Doped
Hide Explanation
Answer.3. Heavily Doped

Ques.41. Inverter Converts

1. DC To AC
2. AC To DC
3. DC To DC
4. AC To AC
Hide Explanation
Answer.3. DC To AC
Explanation:

Ques.42. The Latching Current Of An SCR Is 12 Ma. Its Holding Current

Will Be
1. 4 Ma
2. 12 Ma
3. 50 Ma
4. 8 Ma
Hide Explanation
Answer.1. 4 Ma
Explanation:
The Typical Ratio Of Latching Current To Holding Current Lies In The
Range Of 2.5 To 3. Here For Calculation, We Are Taking The Value Of
Latching Current 3
Latching Current/Holding Current = 3
Given
Latching Current = 12
12/Holding Current = 3
Holding Current = 4

Ques.43. In Series Connected Thyristors

1. L Is Used For Tuning Out Junction Capacitance
2. L & C Is Used For Filtering Out The Ripple
3. R, C Is Called Snubber Circuit
4. L Is Intended To Increase Di/Dt At Switch On
Hide Explanation
Answer.3. R, C Is Called Snubber Circuit

The RC Circuit (Snubber) Acts As A Lowpass Filter For This Voltage

Transient. The Resistance Has Normally Low Value So That The Transient Is
Absorbed By The Capacitor Quickly. Thus The Thyristor Is Protected
Against Voltage Transients. The RC Snubber Circuit Is Very Commonly
Used For Protection Of Thyristors Against Transient Voltages (High-
Frequency Voltage Spikes).

Ques.44. When Thyristor And Transistor As A Switch Are Compared, The

True Statement Is
1. Thyristor Requires Turns Off Circuit While Transistor Does Not
2. The Voltage Drop Of The Thyristor Is Less Than Transistor
3. Thyristor Requires A Continuous Gate Current
4. Transistor Does Not Draw Continuously Base Current
Hide Explanation
Answer.1. Thyristor Requires Turns Off Circuit While Transistor Does Not
Explanation:

Ques.45. In DC Chopper, The Waveform For Input And Output Voltages Are
Respectively
1. Both Discontinuous
2. Both Continuous
3. Continuous, Discontinuous
4. Discontinuous, Continuous
Hide Explanation
Answer.3. Continuous, Discontinuous

Ques.46. In DC Chopper, Per Unit Ripple Is Maximum When Duty Cycle Α

Is
1. 0.1
2. 0.3
3. 0.5
4. 0.7
Hide Explanation
Answer.3. 0.5
Ques.47. In A Step-Up Chopper Circuit, If Vs Is The Source Voltage And Α
Is Duty Cycle, Then The Output Voltage Is
1. Vs/(1 + Α)
2. Vs(1 + Α)
3. Vs(1 − Α)
4. Vs/(1 − Α)
Hide Explanation
Answer.4. Vs/(1 − Α)
During Off-Period Of Switch S. As The Current Tends To Decrease, The
Polarity Of Induced Emf Across L Is Reversed.

The Average Value Of Output Voltage Is Always Less Than Or Equal To

Supply Voltage In Step Down The Chopper. But In The Step-Up Chopper,
The Output Voltage Is More Than The Supply Voltage.
The Value Of Average Output Voltage Is
 Vo = Vs/(1 – Α)

Ques.48. When Emitter Terminal Of A UJT Is Open Then The Resistance Of

The Base Terminal Is
1. Very High
2. Very Low
3. Moderate
4. Any Finite Value
Hide Explanation
Answer.4. Very High
Ques.49. A Half-Controlled Single-Phase Bridge Rectifier Is Supplying An
R-L Load. It Is Operated At A Firing Angle A And The Load Current Is
Continuous. The Fraction Of Cycle That The Freewheeling Diode Conducts
Is
1. Α/ Π
2. Α
3. Π + Α
4. Π − Α
Hide Explanation
Answer.1. Α/ Π
Explanation:

Ques.50. If The Firing Angle In An SCR Rectifier Is Decreased, The Output

Is
1. Increased
2. Maximum
3. Decreased
4. Remain Unaffected
Hide Explanation
Answer.1. Increased

Ques.51. A SCR Is A ________ Switch

1. One Directional
 2. Two Directional
3. Three Directional
4. Four Directional
Hide Explanation
Answer.1. One Directional
Ques.52. Comparing A Triac & SCR
1. Both Are Unidirectional Devices
2. An SCR Has Less Time For Turn Off Than Triac
3. Both Are Bidirectional Devices
4. All Of The Above
Hide Explanation
Answer.2. An SCR Has Less Time For Turn Off Than Triac
Explanation:-

Ques.53. Which Of The Following Statement Is True About Thyristor

1. The Turn Off Time Of A Thyristor Is Less Than The Turn-On Time
2. The Turn-On Time Is Less Than The Turn-Off Time
3. The Turn-Off Time For The Line Commutation Is Less Than The
Forced Commutation
4. None Of The Above
Hide Explanation
Answer.2. The Turn-On Time Is Less Than The Turn-Off Time

Ques.54. In A Three-Phase Halfwave Rectifier, The Ratio Of Average Output

Voltage To Per Phase Maximum AC Voltage Is
1. 1
2. 1.169
3. 0.827
4. 1.571
Hide Explanation
Answer.3. 0.827
Explanation:-
The Average D.C Output Voltage For A Phase Half-Wave Rectifier Is 0.827
Of The Peak.
Dcavg = 0.827 × Vpeak
So Ratio Of Average Output Voltage To Per Phase Maximum AC Voltage
= Dcavg ⁄ Vpeak = 0.827 V

Ques.55. The Figure Represents The

1. Zener Diode
2. Silicon Controlled Rectifier
3. Junction Field Effect Transistor
4. Tunnel Diode
Hide Explanation
Answer.3. Junction Field Effect Transistor

Ques.56. In A 3-Phase Half Wave Rectifier Circuit, Each Diode Is Subjected

To A PIV Od
1. Vm
2. √2Vm
3. √3Vm
4. 2Vm
Hide Explanation
Answer.3. √3Vm

Ques.57. In A Three-Phase Halfwave Rectifier, The Ratio Of Average Output

Voltage To Per Phase Maximum AC Voltage Is
1. 0.955
 2. 1.169
3. 0.827
4. 1.571
Hide Explanation
Answer.1. 0.955
Explanation:-
The Average D.C Output Voltage For A Phase Half-Wave Rectifier Is 0.827
Of The Peak.
Dcavg = 0.955 × Vpeak
So Ratio Of Average Output Voltage To Per Phase Maximum AC Voltage
= Dcavg ⁄ Vpeak = 0.955 V

Ques.58. In A 1φ, Half Wave Controlled Rectifier If The Input Voltage Is

400 Sin314t, The Average Output Voltage For A Firing Angle Of 60° Is
1. 100/Π
2. 200/Π
3. 300/Π
4. 400/Π
Hide Explanation
Answer.4. 400/Π
Explanation:-
The Average Output Voltage Of 1φ, Half Wave Controlled Rectifier Is
Vo = (Vm/2π) X (1+Cosα)

Where
Vm = Maximum Voltage
Vm = 400
400/2π X (1+Cos60) = 300/Π.

Ques.59. Among This Alternative, PIV Rating Of Which Diode Is Lower

Than That Of Equivalent Vacuum Diode?
1. PN Junction Diode
2. Crystal Diode
3. Tunnel Diode
4. Small Single Diode
Hide Explanation
Answer.2. Crystal Diode

Ques.60. In A 3-Φ Semi Converter For Firing Angle Less Than Or Equal To
60°, Wheeling Diode Conducts For
1. Zero Degree
2. 30°
3. 45°
4. 75°
Hide Explanation
Answer.1. Zero Degree

Ques.61. The Fully Controlled Thyristor Converter In The Figure Is Fed

From A Single-Phase Source. When The Firing Angle Is 0°, The DC Output
Voltage Of The Converter Is 300 V. What Will Be The Output Voltage For A
Firing Angle Of 60°, Assuming Continuous Conduction?
1. 300
2. 150
3. 200
4. 700
Hide Explanation
Answer.2. 150
Explanation:-
The Output Voltage Of A Fully Controlled Single Phase Rectifier Is Given
By
Vo = 2Vmcosα/Π
Now At Α = 0° Dc Output Is 300 V
300 =2Vmcos0°/Π
300 =2Vm/Π————(1)
For Firing Angle 60° The Output Voltage Will Be
Vo = 2Vmcos60°/Π
Putting The Value Of 2Vm/Π In Equation 1 We Get
Vo = 300cos60°
Vo = 150 V
Ques.62. In A 3-Phase Voltage Source Inverter Used For Speed Control Of
Induction Motor, Antiparallel Diodes Are Used Across Each Switching
Device. The Main Purpose Of Diodes Is To:
1. Protect The Switching Devices Against Overvoltage
2. Provide The Path For Freewheeling Current
3. Allow The Motor To Return Energy During Regeneration
4. Help In Switching Off The Devices
Hide Explanation
Answer.3. Allow The Motor To Return Energy During Regeneration
.

Ques.63. In A 1-Φ Full Converter, Number Of Scrs Conducting During An

Overlap
1. 2
2. 4
3. 6
4. 8
Hide Explanation
Answer.2. 4
Explanation:-

Ques.64. A Three-Phase AC To DC Diode Bridge Rectifier Is Supplying

From A Three-Phase, 440 V Source. The Rectifier Supplies A Purely
Resistive Load. The Average DC Voltage Across The Load Will Be V
1. 594.20
2. 1029.20
3. 840.40
4. 320.20
Hide Explanation
Answer.2. 1029.20

Ques.65. If The PIV Rating Of A Diode Is Exceeded

1. The Diode Conducts Poorly
2. The Diode Behaves Like A Tunnel Diode
 3. The Diode Is Destroyed
4. The Diode Behaves Like A Capacitor
Hide Explanation
Answer.3. The Diode Is Destroyed
Explanation:-
Ques.66. A Forward Bias PN Junction Will Act As A/An:
1. Amplifier
2. Open Switch
3. Closed Switch
4. Attenuator
Hide Explanation
Answer.3. Closed Switch
Explanation:-

Ques.67. In The Case Of Full Wave Rectifier, The Ripple Factor Is

1. 0.48
2. 0.5
3. 1.51
4. 1
Hide Explanation
Answer.1. 0.48

Ques.68. For A Certain Transistor, If The Value Of Beta Is Equal To 500

And Base Current Is 5ma, Then The Value Of Emitter Current Is:-
1. 2.5A
2. 2A
3. 3A
4. 2.505
Hide Explanation
Answer.4. 2.505
Explanation:-
Given Base Current IB = 5ma
Current Gain Β = 500
The Dc Current Gain Βdc Is Defined As The Ratio Of Collector Current To
Base Current At A Constant VCE Under Dc Biasing Conditions.
Β = IC/IB
500 = IC/50
IC = 2500 Ma
The Emitter Current Is
IE = IB + IC
IE = 50 +2500
IE = 2505ma = 2.505 A

Ques.69. Which Among The Characteristics Of The Crystal Diode Is Used

For Rectification?
1. Opposite
2. Can’t Be Determined
3. Forward Or Reversed
4. Forward
Hide Explanation
Answer.4. Forward

Ques.70. Which Among The Following Indicates Early Effect In BJT?

1. Zener Breakdown
2. Base Narrowing
3. Avalanche Breakdown
4. Thermal Breakdown
Hide Explanation
Answer.2. Base Narrowing

Ques.71. When The Collector Junction In A Transistor Is Biased In The

Reverse Direction And The Emitter Junction In The Forward Direction, The
Transistor Is Said To Be Is The:-
1. Saturation
2. Cutoff Region
3. Active Region
4. None Of These
Hide Explanation
Answer.3. Active Region
Explanation:-
.
Ques.72. In A BJT The Base Current(IB) Is About ______ Of Emitter Current
(IE)
1. 5%
2. 20%
3. 25%
4. 35%
Hide Explanation
Answer.1. 5%
Explanation:-

Ques.73. Among These Which One Is Correct About The Characteristics Of

The Transistor?
1. It Has Very Low Input Impedance
2. It Has Zero Input Impedance
3. It Has The High Input Impedance
4. It Has Low Input Impedance
Hide Explanation
Answer.3. It Has The High Input Impedance

Ques.74. A Transistor When Connected In CE Mode Has:-

1. A Medium Input Resistance And Low Output Resistance
2. A Low Input Resistance And Low Output Resistance
3. A Low Input Resistance And High Output Resistance
4. A High Input Resistance And High Output Resistance
Hide Explanation
Answer.1. A Medium Input Resistance And Low Output Resistance

Ques.75. If The Cathode Of The Thyristor Is Made +Ve With Respect To

The Anode & No Gate Current Is Applied Then:-
1. Only The Middle Junction Is Forward Biased
2. Only The Middle Junction Is Reversed Biased
3. All The Junction Are Forward Biased
4. All The Junction Are Reversed Biased
Hide Explanation
Answer.1. Only The Middle Junction Is Forward Biased

Ques.76. The ________ Region Has The Highest Area In The Transistor
1. Base
2. Collector
3. Base-Emitter
4. Emitter
Hide Explanation
Answer.2. Collector
Explanation:-
A Bipolar Junction Transistor (BJT) Is A Three-Layer, Two Junction
Semiconductor Device Consisting Of Either Two N-Type And One P-Type
Layer Of Material (NPN Transistor) Or Two P-Type And One N-Type Layer
Of Material (PNP Transistor).

Ques.77. Which Configuration In Bipolar Junction Transistor Is Also Known

As Voltage Follower Circuit?
1. Common Base
2. Common Collector
3. Common Emitter
4. None Of These
Hide Explanation
Answer.2. Common Collector

Ques.78. The Effective Turning Off SCR After The Anode Current Has
Reached Zero Value.
1. The Charge Is Removed By Applying Reverse Anode-Cathode Voltage
2. Chargers Are Injected By Applying Reverse Anode-Cathode Voltage
3. Chargers Are Injected By Applying The Gate Signal
4. None Of These
Hide Explanation
Answer.1. The Charge Is Removed By Applying Reverse Anode-Cathode
Voltage
Explanation:-

Ques.79. In The Forward Blocking Mode, The Middle Junction (J2) Has The
Characteristics Of That Of A:
1. Inductor
2. Transistor
3. Capacitor
4. None Of These
Hide Explanation
Answer.3. Capacitor

Ques.80. During The Transition Time Or Turn On Time

1. The Forward Anode Voltage Is Increased From 10% To 90% & The
Anode Current Decreases From 90% To 10% Of The Initial Value
2. The Forward Anode Voltage Is Decreased From 90% To 10% & The
Anode Current Decreases From 90% To 10% Of The Initial Value
3. The Forward Anode Voltage Is Decreased From 90% To 10% & The
Anode Current Increases From 10% To 90% Of The Initial Value
4. The Forward Anode Voltage Is Increased From 10% To 90% & The
Anode Current Also Increases From 10% To 90% Of The Initial Value
Hide Explanation
Answer.3. The Forward Anode Voltage Is Decreased From 90% To 10%
& The Anode Current Increases From 10% To 90% Of The Initial Value
Explanation:-

Ques.81. The Forward Dv/Dt Rating Of An SCR:-

1. Decrease With The Decrease In The RMS Value If Forward Anode-
Cathode Voltage
2. Decrease With The Increase In The Junction Temperature
3. Increase With An Increase In The Junction Temperature
4. Increase With The Decrease In The RMS Value Of Forward Anode-
Cathode Voltage
Hide Explanation
Answer.3. Increase With An Increase In The Junction Temperature
Explanation:-
Ques.82. The Two Transistor Model Of The SCR Can Be Obtained By:-
1. Bisecting The SCR Vertically
2. Bisecting The Scrs Middle Two Layer
3. Bisecting The SCR Horizontally
4. Bisecting The Scrs Top Two And Bottom Two Layers
Hide Explanation
Answer.4. Bisecting The Scrs Top Two And Bottom Two Layers

Ques.83. Latching Current For An SCR Is 100 Ma, A Dc Source Of 200 V Is

Also Connected To The SCR Which Is Supplying An R-L Load. Compute
The Minimum Width Of The Gate Pulse Required To Turn On The Device.
Take L = 0.2 H & R = 20 Ohm Both In Series.
1. 81 Μsec
2. 100.5 Μsec
3. 62.7 Μsec
4. 56.9 Μsec
Hide Explanation
Answer.2. 100.5 Μsec
Explanation:-

Ques.84. What Is The Most Suitable Method To Turn On The SCR Device
Among The Following?
1. Gate Triggering Method
2. Forward Voltage Triggering Method
3. Temperature Triggering Method
4. Dv/Dt Triggering Method
Hide Explanation
Answer.1. Gate Triggering Method
Ques.85. What Is The Total Anode Current Of SCR In The Equivalent
Circuit From The Two Transistors (T1 & T2) Analogy Of SCR?
1. The Sum Of Both Base Current
 2. The Sum Of Both Collector Current
3. The Sum Of The Base Current Of T2 & Collector Current Of T1
4. The Sum Of The Base Current Of T1 & Collector Current Of T2
Hide Explanation
Answer.2. The Sum Of Both Collector Current

Ques.86. For An SCR, The Gate-Cathode Characteristics Have A Slope Of

130. The Gate Power Dissipation Is 0.5 Watt. Find Ig.
1. 6.2 Ma
2. 0.62 A
3. 620 Ma
4. 62 Ma
Hide Explanation
Answer.4. 62 Ma

Ques.87. When Both The Junctions Of Bipolar Junction Transistor (BJT)

Are In Forward Biased, Then In Which Region BJT Will Operate?
1. Ohmic Region
2. Cut-Off Region
3. Saturation Region
4. Active Region
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Answer.3. Saturation Region

Ques.88. What Kind Of Device Is A Field Effect Transistor?

1. Non-Semiconductor
2. Unipolar Semiconductor
3. Bipolar Semiconductor
4. Insulator
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Answer.2. Unipolar Semiconductor
Explanation:-
Ques.89. The Value Of Anode Current Required To Maintain The
Conduction Of An SCR Even Though The Gate Signal Is Removed Is Called
As The:-
1. Latching Current
2. Holding Current
3. Switching Current
4. All Of These
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Answer.1. Latching Current

Ques.90. Consider An N-Channel MOSFET Having Width W, Length L And

Electron Mobility In The Channel Is µn And Capacitance Per Unit Area Is
C_Ox. If Gate To Source Voltage V_GS = 0.7V, Drain To Sour Voltage
V_DS = 0.2 V, µ_Nc._Ox = 120µa/V, Threshold Voltage V_T = 0.4V And
(W/L) = 60. Calculate The Transconductance Gm In Ma/V
1. 2.5ma
2. 1.65ma
3. 3ma
4. 1.44ma
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Answer.4. 1.44ma

Ques.91. What Is The Value Of Β In A Transistor Having IC = 100.2ma And

IE = 100ma?
1. 101
2. About 1
3. 501
4. 201
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Answer.3. 501

Ques.92. Which Of The Following Are The Functions Of A Transistor?

1. Rectifier And Fixed Resistor
2. Switching Device And Fixed Resistor
 3. Tuning Device And Rectifier
4. Variable Resistor And Switching Device
Hide Explanation
Answer.4. Variable Resistor And Switching Device

Ques.93. Number Of Diodes Required In The Ordinary Full-Wave Rectifier

Is
1. 1
2. 2
3. 3
4. 4
Hide Explanation
Answer.2. 2

Ques.94. In A Rectifier Circuit, The Primary Function Of The Filter Is To

1. Control The DC Level Of The Output Voltage
2. Remove Ripples From Rectified Output
3. Minimize AC Input Variations
4. Suppress Odd Harmonics In The Rectifier Output
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Answer.2. Remove Ripples From Rectified Output

Ques.95. A Rectifier For Welding Has Voltage/Current Characteristics As

1. Drooping
2. Rising
3. Static
4. Variable
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Answer.1. Drooping

Ques.96. During Forward Blocking State, The SCR Has

1. Low Current, Medium Voltage
2. Low Current, Large Voltage
 3. Medium Current, Large Voltage
4. Large Current, Low Voltage
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Answer.2. Low Current, Large Voltage

Ques.97. The Function Of SCR Contactor In Resistance Welding Machine Is

1. To Provide An Accurate Weld Time For Each Weld
2. To Connect The Large Power Supply To Welding By Closing A Small
Switch
3. To Provide Full Wave Rectification Of The Welding Current
4. To Avoid Saturation Of Transformation Core
Hide Explanation
Answer.2. To Connect The Large Power Supply To Welding By Closing A
Small Switch

Ques.98. A Single Phase Full Bridge Inverter Is Fed From A 48 V Battery

And Is Delivering Power To A Pure Resistance Load What Is The Value Of
Fundaments Output Voltage?
1. 15.80
2. 22.26
3. 8.36
4. 43.22
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Answer.4. 43.22
Explanation:-
The Output Dc Voltage Of Single Phase Full Bridge Inverter Is Given As
Eo = 2√2Edc/Π
Where
Edc = Input DC Voltage = 48 V
Eo = 2√2 × 48/Π
Eo = 43.22 V

Ques.99. A Three-Phase Diode Bridge Rectifier Is Fed From A 400 V RMS,

50 Hz, Three-Phase AC Source. If The Load Is Purely Resistive, Then Peak
Instantaneous Output Voltage Is Equal To
 1. 400 V
2. √2 × 400
3. 400/√2
4. √2/400
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Answer.2. √2 × 400

Ques.100. The Peak Inverse Voltage, In Case Of A Bridge Rectifier, For

Each, The Diode Is: (Where Eo = Peak Value Of Input Voltage)
1. Eo
2. 2Em
3. 3Em
4. 4Em
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Answer.1. E