1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC- SEMESTER-IV EXAMINATION SUMMER 2017
Subject Code: X40902 Date:29/05/2017
Subject Name: Power Electronics-I
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

Describe construction, characteristics and working of a SCR.
07

List and explain various turn on methods for thyristor. Also give list of gate triggering methods.
07
Q.2

Draw and explain the circuit diagram of TRIAC using DIAC.
07

What is snubber circuit? Why is it needed? Draw such circuit for a SCR and give guidelines for selecting it's components.
07
OR

Explain series and parallel operation of thyristors.
07
Q.3

Explain two transistor analogy of thyristor in detailed.
07

Discuss thermal modeling of thyristor. Why di/dt protection is required?
07
OR
Q.3

List out control strategies adopted to control the output voltage in chopper. Explain 'Step-down Chopper'
07

Explain dual converter based DC drives.
07
Q.4

Draw and explain three phase half wave rectifier with R-L load with necessary waveforms.
07

Enlist different types of power factor improvement techniques for AC to DC converters. Explain any one technique.
07
OR
Q.4

Using relevant circuit diagram and waveforms, explain regenerative braking control in DC machines using chopper circuit.
07

Explain UJT as relaxation oscillator with necessary equations.
07
Q.5

Discuss constant H.P and constant Torque operation of speed control of motors.
07

Explain Buck regulator with necessary circuit diagram waveforms.
07
OR
Q.5

Draw and explain the circuit diagram of TRIAC using DIAC.
07

Compare MOSFET with SCR in terms of basic structure, V-I characteristics, ratings, control principle, applications.
07