1 (a)
What is power electronics? Draw a neat block diagram of generalized power converter system. State the applications of power electronics.

6 M

1 (b)
With neat circuit diagram and waveforms, explain the types of power electronics circuits.

12 M

1 (c)
Compare General-purpose, Fast recovery and Schokky diodes.

2 M

2 (a)
The maximum junction temperature of a transistor is T

_{3}=150°C and the ambient temperature is T_{A}=25°C, if the thermal impedances are R_{JC}=0.4°C/W, R_{es}=0.1°C/W, and R_{SA}=0.5°C/W. Calculate (i) the maximum power dissipation and (ii) the case temperature.
4 M

2 (b)
With the help of parasitic model and switching model, explain the switching wavefoms of n-type (enhancement) MOSFET.

10 M

2 (c)
Write a note on isolation of grate and base drives.

6 M

3 (a)
Using a two model of thyristor, show that \[ I_A=\dfrac {\alpha I_{C}+I_{CBOI}+I_{CBO2}}{1-(\alpha_{1}+\alpha_2)} \]

6 M

3 (b)
With neat sketch, explain turn-on characteristics of SCR.

6 M

3 (c)
The input voltage of Fig.Q3(b) is V

_{s}=200V with load resistance of R=5?. The load and stray inductance are negligible and the thyristor is operated at frequency of f_{s}=2 kHz. If the required dv/dt is 100 V/?s and the discharge current is limited to 100A. Determine (i) the value of R_{s}and C_{s}(ii) the snubber loss, and (iii) the power rating of the snubber resistor.

**dv/dt Protection Circuit**

8 M

4 (a)
Discuss the effect of inductance using the 1-? full converter.

8 M

4 (b)
What is phase control? Explain the principle of phase control using 1-? half wave controlled rectifier.

8 M

4 (c)
Compare circulating and non-circulating mode of operation of dual converter.

4 M

5 (a)
A thyristor circuit is shown in fig.Q5(a), if thyristor T

_{1}is switched on at t=0, determine the conduction time of thyristor are L=10 ?H, C=50?F and V_{3}=200 V. The inductor carries an intial current of l_{m}=250A.

**Self Commulated Circuit**

10 M

5 (b)
What is the principle of complementary commutation? Explain the same with the help of suitable circuit and waveforms.

10 M

6 (a)
What is the principle of on off control? Explain the same with a single phase full-wave controller.

6 M

6 (b)
Draw a neat sketch of 1-? AC voltage controller with RL, load and explain its working .

6 M

6 (c)
A single-phase full wave AC voltage controller has a resistive load R=10? and the input votage is V

(iii) the average current of thyristor I

_{3}=120V (rms), 60Hz. The delay angles of thyristor T_{1}and T_{2}are equal ?_{1}- ?_{2}- ?/2. Determine (i) the rms output voltage V_{0}(ii) the input power factor PF(iii) the average current of thyristor I

_{A}and (iv) the rms current of thyristor I_{R}.
8 M

7 (a)
With a neat circuit diagram, explain the operation of a step down chopper and also explain constant frequency and variable frequency operation. Derive an expression for output voltage incase step down chopper.

10 M

7 (b)
A step-up chopper with a pulse width of 200?s operating on 200V, dc supply. Calculate the output voltage, if the blocking period of the devices is 50?s.

2 M

7 (c)
With a neat mcircuit diagram and quadrant operation, explain class F. chopper.

8 M

8 (a)
With a neat circuit diagram, of 1-0 half bridge inverter, explain the principle of operation of an inverter.

8 M

8 (b)
Write brief note on current source inverter.

6 M

8 (c)
With the help of circuit diagram and waveforms, explain a variable DC-link inverter.

6 M

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