Power Electronics-1 - Dec 2013

Electronics Engineering (Semester 6)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) Draw gate characteristics of SCR.(5 marks) 1 (b) Explain how use of freewheeling diode improves power factor in controlled rectifier. (5 marks) 1 (c) Draw and explain snubber circuit.(5 marks) 1 (d) Explain the use of MOV for overvoltage protection in SCR circuit.(5 marks) 2 (a) Explain the need of equalising circuit in series and parallel connection of SCRs. Draw circuits and explain. (10 marks) 2 (b) Derive different performance parameters in fully controlled bridge converter with R-L load. (10 marks) 3 (a) Draw and explain single phase half controlled rectifier with symmetrical configuration. Draw waveforms. (10 marks) 3 (b) Draw and explain dynamic characteristics of SCR during turn on and turn off process. (10 marks) 4 (a) Explain the role of UJT in triggering the SCR with the help of circuit diagram and waveforms. (10 marks) 4 (b) Draw and explain AC full wave controller circuit using DIAC and TRIAC. Derive the expression for waveforms(10 marks) 5 (a) Draw and explain three phase full wave controlled rectifier with R load.(10 marks) 5 (b) A single phase half wave controlled rectifier is supplied with 230V, 50 Hz supply. Calculate firing angle to get 60V dc output. Also calculate RMS output voltage and form factor if load is resistive.(10 marks) 6 (a) Draw and explain zero voltage switch with integral cycle triggering.(10 marks) 6 (b) Draw electrical equivalent of heat sink. Explain analogy. (5 marks) 6 (c) What do you understand by latch-ups in IGBT? How can it be avoided? (5 marks) 7 (a) GTO switching characteristics. (7 marks) 7 (b) Soft start circuit.(6 marks) 7 (c) SOA for MOSFET. (7 marks)