GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VI EXAMINATION — SUMMER 2020
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Subject Code: 2161708 Date:28/10/2020
Subject Name: POWER ELECTRONICS
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
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MARKS
Q.1 (a) What are the requirements for good base drive of transistor? 03
(b) Explain operation of base drive circuit which is useful when 04 capability of base voltage Vb is low.
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(c) In a full-wave rectifier, load resistance is 3kO. The input 07 voltage is 240sin2p50t. Calculate the maximum value of the current, average current, dc power output and ripple factor.
Q.2 (a) Define reverse recovery time of diode. 03
(b) Explain dynamic characteristics of power MOSFET. 04
(c) With waveforms explain single-phase half-wave controlled 07 rectifier.
OR
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(c) Explain 3-F half-wave rectifier (Resistive Load) with 07 relevant waveforms.
Q.3 (a) What do you mean by Duty Cycle of Chopper? 03
(b) Explain dynamic characteristics of power BJT. 04
(c) Draw symbols and static characteristics of SCR. In which 07 ways it can be fired?
OR
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Q.3 (a) What is meaning of hold time of filter- rectifier? 03
(b) What is freewheeling diode? Explain with an example. 04
(c) Explain operation of step-down converter with waveforms of 07 the various signals of circuit.
Q.4 (a) What are the benefits of isolation between the input and 03 output circuit?
(b) What are the gate drive requirements for a MOSFET? 04
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(c) Explain Type E Chopper 07
OR
Q.4 (a) Define Holding current of SCR. 03
(b) How to calculate power dissipation in BJT? 04
(c) If Chopper is having a supply voltage of 100V DC and 07 operating at a frequency of 5KHz with a pulse width of 65µs. Calculate the duty cycle, average load voltage and RMS load voltage.
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Q.5 (a) Explain Latching current of SCR. 03
(b) Explain two-level chopper using single pole double throw 04 switch.
(c) Explain the operation of the forward converter with 07 waveforms.
OR
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Q.5 (a) Draw and explain Anti saturation circuit for transistor. 03
(b) Write a short note on Boost Converter. 04
(c) Differentiate between self-driven and driven inverter. 07
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