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Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
Fifth semester B.Tech degree examinations (S) September 2020

Course Code: EE305
Course Name: POWER ELECTRONICS

Max. Marks: 100 Duration: 3 Hours
Graph sheets will be provided
PARTA

Answer all questions, each carries 5 marks. Marks
1 Draw the static VI characteristics of a SCR and explain. (5)
2 Explain R firing circuit of SCR with circuit diagram and waveforms. (5)
3 Draw the output voltage waveform of a 3-phase controlled half wave rectifier (5)

for a=30".

4 Explain the working of a single phase half bridge voltage source inverter with (5)

pure R load. Draw the output voltage & output current waveforms and derive an
expression for rms output voltage.

5 For a single phase ACVC with source voltage asv, = 100sinwt, and load (5)
asR = 500, draw the output voltage and current waveforms if Thyristor firing
angle is (1) a=30° (ii) a=90°.

6 Define the terms amplitude modulation index and frequency modulation index. (5)

7 Draw the waveform of inductor voltage of a boost 00-00 converter and obtainan (5)
expression for output ‏عل‎ voltage in terms of input voltage and duty cycle.

8 In a step down chopper the ‏عل‎ input voltage is of JOOV. The MOSFET switch is (5)
having a switching frequency of 2kHz. Find the duty cycle and average ‏عل‎
‎output voltage if the turn on period of switch is 0.2ms.

PART B
Answer any two full questions, each carries 10 marks.

9 Deduce the Two Transistor Model for a Thyristor and explain the Thyristor (10)
operation using this model.
10 a) Describe the variation of current and voltage during turn- on time of an SCR (5)

with the help of characteristics.

b) With circuit diagram and relevant waveforms, explain the operation of UJT (5)

firing circuit for triggering a SCR.

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