1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER-VII EXAMINATION WINTER 2018
Subject Code:X71102 Date: 19/11/2018
Subject Name: Power Electronics
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

Classify the chopper. List all types of chopper and explain any two in detail.
07

Explain di/dt and dv/dt protection for thyristor.
07
Q.2

Explain the natural commutation forced commutation of SCR.
07

What is the need of UPS? Discuss offline UPS system with their operation and features.
07
OR

A step up chopper has an input voltage of 150V. The voltage output needed is 450V. Given, that the thyristor has a conducting time of 150μseconds. Calculate the chopping frequency.
07
Q.3

What is GTO? Draw and Explain GTO structure. Also explain GTO Turn off mechanism with desired equation and figures.
07

Describe the construction working of IGBT along with the advantage of IGBT over BJT MOSFET.
07
OR
Q.3

Describe three phase bridge inverter with 180º mode of conduction.
07

Explain working principle of SCR with its characteristics and two transistor models.
07
Q.4

List types of heating mechanism available and Explain any one in detail.
07

Explain battery charger with necessary diagrams.
07
OR
Q.4

Give classification of thyristor family. Draw explain TRIAC in detail.
07

Draw explain single phase full converter with resistive load using required
Waveforms.
07
Q.5

Draw and explain the structure of power MOSFET. Also explain working principle and V-I characteristics of power MOSFET.
07

Describe SMPS with necessary diagrams in detail.
07
OR
Q.5

Explain the working principle of Buck regulator with the help of circuit diagram and waveforms. Draw equivalent circuit for different modes of operation.
07

Define following terms
1. Latching current 2. The holding current 3. On state voltage
4. Forward dv/dt rating 5. Commutation 6. Firing angle
7. Duty cycle
07