[9 06000EE305122001 Pages: 3

Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
Fifth Semester B.Tech Degree Regular and Supplementary Examination December 2020

Course Code: EE305
Course Name: POWER ELECTRONICS

Max. Marks: 100 Duration: 3 Hours
(Graph sheets may be supplied on demand)
PARTA
Answer all questions, each carries5 marks. Marks
1 Discuss how a thyristor may be subjected to over voltages. Discuss the method (5)

adopted for protect the thyristor from such over voltages.

2 What are the main features that the firing circuits for thyristors should possess? (5)
Give the general layout of a firing circuit scheme and explain the function of
various components used in it.

3 Compare circulating mode of operation of dual converter and non-circulating (5)
mode of operation of dual converter.

4 With neat circuit diagram, output voltage and output current waveforms, (5)

explain the working of single phase half bridge inverter with RL load.

5 Explain sinusoidal pulse modulation as used in PWM inverters. (5)

6 Explain with circuit diagram and waveforms, the working of a single phase (5)
ACVC with R load.

7 Describe the principle of step up chopper. Sketch the input voltage, input (5)

current, output voltage and output current waveform. Derive an expression for
the average output voltage in terms of input voltage and duty cycle.

8 The buck regulator has an input voltage 15 V. The average output voltage 155 (5)
V at R = 1 kQ and the peak to peak output voltage ripple is 15 mV. The
switching frequency is 30 kHz. If the peak to peak ripple current of inductor is
limited to 0.5 A, find a) the duty cycle

b) the filter inductance

c) the filter capacitance