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Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
V SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2018
Course Code: EE305
Course Name: POWER ELECTRONICS
Max. Marks: 100 ١ Duration: 3 Hours

Graph sheets may be supplied on demand

PART A
Answer all questions, each carries 5 marks. Marks
1. Define holding current and latching current of SCR. Show these currents on the (5)
static IV characteristics of SCR.
2 With the help of circuit diagram and waveform, explain the operation of RC (5)

triggering circuit for one thyristor.

3. A three phase half wave converter is operated from 3—phase, 230 ५, 50Hz (5)
supply with load resistance R= 10Q. An average output voltage of 50% of the
maximum possible output voltage is required. Determine i) the firing angle, ii)
average and rms values of load current.

4. With the help of circuit diagram explain the working of current source inverter. (5)
5. What is pulse width modulation? List the various PWM techniques. (5)
6. Explain the principle of phase control in a single phase ac voltage controller. (5)
7 Draw the circuit of step up chopper and explain its working. (5)
8. For a type A chopper, de source voltage is 230 ‏,لا‎ load resistance 10 Q, drop (5)

across the switch is 2Vand duty cycle 0.4. Calculate average and RMS value of
output voltage and chopper efficiency.

PART B
Answer any two full questions, each carries10 marks.

9 a) Discuss the condition which must be satisfied for turning on the SCR witha (5)
gate signal.
b) Explain the significance of di/dt protection in thyristors and describe the (5)

method employed for improving the same.

10 With the help of circuit diagram explain the working of single phase fully (10)
controlled converter with RL load. Draw the waveform of output voltage with
and without freewheeling diode and output current.

11 a) What are the steps to be employed to prevent the difficulties of parallel (4)
operation of thyristors?

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