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INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Answer any one question from Q1 and Q2
1 (a) Draw two transistor analogy of SCR and derive an expression for its anode current IA?
7 M
1 (b) Draw & explain single phase fully controlled rectifier (full converter) for R-L load with various o/p voltage wavefoRMS.
7 M
1 (c) Single phase full bridge inverter is operated from 48V DC supply, it has a resistive load of R = 2.4 Ω Find:
i) RMS o/p voltage at fundamental frequency (VO1)
ii) RMS o/p power
iii) RMS o/p voltages at second & third harmonic (VO2 & VO3)
6 M

2 (a) Draw construction diagram of n-channel enhancement type MOSFET and explain its steady state charACteristics.
7 M
2 (b) Draw & explain three phase half controlled bridge converter for R load with o/p voltage wavefoRMS.
7 M
2 (c) Compare 120° mode with 180 0 mode in three phase inverter for balanced star R load.
6 M

Answer any one question from Q3 and Q4
3 (a) Explain operation of step up chopper with circuit diagram and derive an expression for its o/p voltage: $V_o= \dfrac {V_s}{(1-D)}$ where D is duty cycle.
6 M
3 (b) A DC chopper with R-L load is operated from 220V DC supply. The load parameters are R = 5Ω , L = 7.5 mH and chopping frequency Fc = 1KHz. If peak to peak load ripple current is maximum, calculate:
iii) Peak to peak load ripple current
6 M
3 (c) Explain various control strategies in DC chopper.
6 M

4 (a) Explain operation of four quadrant chopper with circuit diagram.
6 M
4 (b) Explain with block schematic working of SMPS. What are its advantages over linear power supply.
6 M
4 (c) A single phase full wave AC voltage controller has a resistive load of R = 10Ω and the input voltage is Vs = 120 V(RMS), 50 Hz. The delay angles of thyristors T1 and T2 are equal : a1 = a2 = π/2. Determine
i) the RMS output voltage
ii) the RMS output current
iii) the input PF
6 M

Answer any one question from Q5 and Q6
5 (a) Explain with block schematic working of On-line & off-line UPS.
8 M
5 (b) The speed of a separately excited DC motor (armature) is controlled by a 1-¢ semi-converter. The field current is also controlled by a 1-¢ semi converter and is set to its maximum possible value. The AC supply to both armature & field converters is single phase 208V, 60Hz. The armature resistance Ra=0.275Ω. Field resistance Rf=147Ω. The motor voltage constant Kv=0.7032 V/A. rad/s, the armature & field currents are continuous & ripple free. If load torque TL=45 N-m at 1000 RPM, calculate:
i) Field current If
ii) BACk emf Eg
iii) Firing angle of converter in armature circuit
iv) Input power fACtor of armature circuit converter.
8 M

6 (a) Explain voltage & frequency control method for 3-¢ induction motor drive in detail.
8 M
6 (b) What are advantages of electronic ballast over conventional ballast? Explain working of electronic ballast with block schematic.
8 M

Answer any one question from Q7 and Q8
7 (a) What is EMI? Explain various sources & minimizing techniques of EMI.
6 M
7 (b) For a thyristor, Maximum junction temperature is 125°C. The thermal resistances are ϕJC=0.16, ϕCS=0.08°C/W, for heat sink temperature of 70°C, calculate total average power loss in thyristor-sink combination.
If heat sink temperature is reduced to 60°C, find new total average power loss in thyristor-sink combination.
4 M
7 (c) Write a note on 'over voltage protection' in power electronics.
6 M

8 (a) What is the need of resonant converter? Explain ZCS resonant converter with circuit & waveforms.
8 M
8 (b) Explain SLR half bridge DC-DC converter in low frequency with suitable waveforms.
8 M

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