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Power Electronics

Study 217 Electrical Engineering MCQs with correct answers and explanations.

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111Electrical EngineeringMedium

Materials used in heat sink should have________?

Alarge surface area

Bhigh melting point

CAll of these

Dhigh thermal conductivity

Correct answer

C. All of these

Explanation

The correct answer is All of these.

112Electrical EngineeringMedium

For a buck converter to reduce the conduction losses in diode

AA high on – resistance switch can be added in series

BA low on – resistance switch can be added in parallel

CA high on – resistance switch can be added in parallel

DA low on – resistance switch can be added in series

Correct answer

D. A low on – resistance switch can be added in series

Explanation

The correct answer is A low on – resistance switch can be added in series.

113Electrical EngineeringMedium

A combination of synchronized leading edge and trailing edge modulation has also been used to control a________?

ANone f these

BA buck dc – dc converter to reduce ripple in the intermediate dc bus capacitor

CBoost single – phase power factor converter

DBoth A. and B.

Correct answer

D. Both A. and B.

Explanation

The correct answer is Both A. and B..

114Electrical EngineeringMedium

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

AZero

BPositive

CNegative

DNone of these

Correct answer

B. Positive

Explanation

The correct answer is Positive.

115Electrical EngineeringMedium

The typical value of SCR for modern alternator is________?

A1.2.

B1.0.

C1.5.

D0.5.

Correct answer

D. 0.5.

Explanation

The correct answer is 0.5..

116Electrical EngineeringMedium

Let of a thyristor Vc1, Vc2, Vc3 are forward break over voltage for gate current Ig1, Ig2, Ig3 respectively. Then________?

AVc1 > Vc2 > Vc3 when Ig1 Ã¢â€°Â¥ Ig2 &Atil

BVc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3.

CVc1 = Vc2 = Vc3 any value of Ig.

Correct answer

B. Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3.

Explanation

The correct answer is Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3..

117Electrical EngineeringMedium

An SCR is made up of silicon because?

ASilicon has a larger leakage voltage than germanium

BSilicon has a smaller leakage voltage than germanium

CSilicon has a larger leakage current than germanium

DSilicon has a smaller leakage current than germanium

Correct answer

D. Silicon has a smaller leakage current than germanium

Explanation

The correct answer is Silicon has a smaller leakage current than germanium.

118Electrical EngineeringMedium

In variable frequency, PWM gain

APhase lag helps to decrease the phase margin of the control loop

BPhase lead helps to increase the phase margin of the control loop

CPhase lead helps to decrease the phase margin of the control loop

DPhase lag helps to increase the phase margin of the control loop

Correct answer

B. Phase lead helps to increase the phase margin of the control loop

Explanation

The correct answer is Phase lead helps to increase the phase margin of the control loop.

119Electrical EngineeringMedium

During reverse recovery time________?

Acharge carrier of junction J2 recombined

Bcharge carrier of junction J3 is swept out

Ccharge carrier of junction J1 is swept out

Dboth B and C

Correct answer

D. both B and C

Explanation

The correct answer is both B and C.

120Electrical EngineeringMedium

The function of snubber circuit connected across the SCR is to________?

ADecrease dV / dt.

BIncrease dV / dt.

CSuppress dV / dt.

DDecrease di / dt.

Correct answer

C. Suppress dV / dt.

Explanation

The correct answer is Suppress dV / dt..

For a buck converter to reduce the conduction losses in diode

AA high on – resistance switch can be added in series

BA low on – resistance switch can be added in parallel

CA high on – resistance switch can be added in parallel

DA low on – resistance switch can be added in series

Correct answer

D. A low on – resistance switch can be added in series

Explanation

The correct answer is A low on – resistance switch can be added in series.

An SCR is made up of silicon because?

ASilicon has a larger leakage voltage than germanium

BSilicon has a smaller leakage voltage than germanium

CSilicon has a larger leakage current than germanium

DSilicon has a smaller leakage current than germanium

Correct answer

D. Silicon has a smaller leakage current than germanium

Explanation

The correct answer is Silicon has a smaller leakage current than germanium.

In variable frequency, PWM gain

APhase lag helps to decrease the phase margin of the control loop

BPhase lead helps to increase the phase margin of the control loop

CPhase lead helps to decrease the phase margin of the control loop

DPhase lag helps to increase the phase margin of the control loop

Correct answer

B. Phase lead helps to increase the phase margin of the control loop

Explanation

The correct answer is Phase lead helps to increase the phase margin of the control loop.