Power Electronics Question Paper - Dec 16 - Electronics Engineering (Semester 7)

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Power Electronics - Dec 16

Electronics Engineering (Semester 7)

Total marks: 80
Total time: 3 Hours INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.

Answer any four

1.a. Explain dynamic characteristics of SCR

(5 marks) 00

1.b. Compare IGBT and Power BJT

(5 marks) 00

1.c. What is need of free wheeling diode in rectifiers with example.

(5 marks) 00

1.d. Draw and explain DIAC characteristics

(5 marks) 00

1.e. What is the need of thyristors in Electronic Circuits?

(5 marks) 00

2.a. Draw and explain full controlled rectifier with $\mathrm{R}-\mathrm{L}$ load . Draw waveforms when $\mathrm{a}=60^{\circ}$

(10 marks) 00

2.b. Explain working of step up Chopper with-proper waveforms.

(10 marks) 00

3.a. A single phase half bridge inverter has resistive load of 8 ohms and $\mathrm{DC}$ input voltage $\mathrm{E} \mathrm{dc}=50 \mathrm{V}$ Calculate:

(i) RMS output Voltage

(ii) Average and Peak current of each Thyristor

(iii) Output Power Po

(10 marks) 00

3.b. Explain voltage control technique in Inverter using sinusoidal PWM method

(10 marks) 00

4.a.

(10 marks) 00

4.b.

(10 marks) 00

5.a. Explain Power MOSFET construction and characteristics. Give one application.

(10 marks) 00

5.b. Design relaxation oscillator circuit for SCR using UJT for following data: $\eta=0.74, \mathrm{Ip}=0.5 \mathrm{mA}, \mathrm{Vp}=16 \mathrm{V}, \mathrm{Iv}=2.5 \mathrm{mA}, \mathrm{Rbb}=5.5 \mathrm{K} \Omega$ , with emitter open. The firing frequency is $3 \mathrm{KHz}, \mathrm{C}=0.047 \mu \mathrm{F}$

(10 marks) 00

Write short notes on

6.a. Buck-Boost mode regulator

(5 marks) 00

6.b. Protection circuits for SCR.

(5 marks) 00

6.c. Cyclo-converters and applications

(5 marks) 00

6.d. Forced commutation in SCR

(5 marks) 00

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