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06000EE305122001

PART B
Answer any two full questions, each carries 10 marks.
Draw the two-transistor model of a thyristor. Derive an expression for the

anode current and based on that, discuss the turn on mechanism of a thyristor
using gate triggering.
Explain the structure and principle of operation of a power diode.
Discuss the problems associated with parallel operations of SCR and how these
are overcome.
Draw the RC full wave triggering circuit of SCR and explain with relevant
waveforms.
A single phase fully controlled bridge rectifier feeds power to a resistive
inductive load without a freewheeling diode across the load. Explain the
continuous mode of operation with circuit diagram. Draw waveforms for source
voltage, load voltage, load current and voltage across the SCR for a given firing
angle ൨.
Derive an expression for average and RMS load voltages of single phase fully
controlled bridge rectifier with RL load without a freewheeling diode across the
load in terms of source voltage and firing angle. Assume continuous
conduction.
PART ^

Answer any two full questions, each carries 10 marks.

A three phase semiconverter is connected to RLE load. Explain its working

with neat circuit diagram and waveforms at firing angle 0 = 60° and a = 120°.
Explain the four quadrant operation of a single phase dual converter with
circulating mode.
Explain the working of CSI with neat circuit diagram and waveforms.
Illustrate the operation of a three phase voltage source bridge inverter operating
in 120° conduction mode with output line voltage and phase voltage
waveforms.
PART 0

Answer any two full questions, each carries 10 marks.
What is pulse width modulation? Define the terms modulation index and
frequency modulation ratio.

A single phase full wave ACVC has a resistive load of 10 ൨ and the input

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