Power Semiconductor Devices

UNIT-I

POWER SEMICONDUCTOR DEVICES

PART-A

1. Draw the turn-on Characteristics of SCR and markthe timings td,,trand ton.

2. What are the factors that influence the turn-offtime of thyristor?

3. What are the parameters involved in switching loss of power device?

4. What are methods of turn-on the SCR?

5. What is latching current of SCR?

6. Why IGBT’s are becoming popular in their applications to controlled converter?

7. In TRIAC’s which of the modes of the sensitivityof gate is high.

8. Define the term pinch of voltage of MOSFET.

9. State the advantages of IGBT over MOSFET.

10. What is the function of snubber circuit?

11. Draw the turn-on Characteristics of TRIAC and mark the timings td, trand ton

. PART-B

1. Discuss the different modes of operation of thyristor with the help of its static V-I

characteristics. (8)

(b) Explain why triac is rarely operated in I quadrant with -ve gate current & in III

quadrant +ve gate current. (8)

2.(a) Describe the structure of an IGBT. (8)

(b) Draw the simplified model of a MOSFET to show the interelectrode capacitance. (8)

3. Explain the four modes of operation of a TRIACCompare their sensitivity. (16)

4. Draw the dynamic characteristics of SCR during turn-on and turn-off and explain. (16)

5. Describe any one driver circuit and snubber circuit for MOSFET. (16)

6. Write short notes on:

(a) Snubber circuit of BJT (8)

(b) commutation circuit of SCR (8)

7. (a) Draw and explain the forward characteristics of SCR using two transistor model ofSCR.

(10) (b) Compare any six salient features of MOSFET & IGBT. (6

UNIT-II

PHASE CONTROLLED RECTIFIERS

PART-A

1) State the principle of phase control in AC-DC converter.

2) Why is power factor of semi-converter than full converter?

3) What is the inversion mode of rectifiers?

4) Write the expression for output DC Voltage in asingle phase full controlled converter.

5) Define total harmonic distortion (THD).

6) Define Distortion factor.

7) Write any four performance parameter of a phasecontrolled rectifiers?

8) What is a dual Converter?

9) What are the advantages of three-phase converterover single phase converter.

10) Draw the O/P Voltage of the Converter as a function of firing angle.

PART – B

1. Discuss the operation of single phase half controlled rectifier with inductive load. Derive

the average output voltage equation. (16)

2. Explain the principle of operation of single phase dual converter with neat power circuit

diagram. (16)

3. Explain the operation of three phase half controlled rectifier supplying R- load with

neat waveforms. Derive an expression for the average output voltage. (16)

4. With necessary circuit and waveforms explain theprinciple of operation of single

Phase fully controlled converter. Derive the expression for average output voltage. (16)

5. Explain the effect of source inductance in theoperation of single phase fully

controlled converter. Derive the expression for its output voltage. (16)

6. Explain the operation of three -phase full converter. Derive expression for its average output

voltage. (16)

7. A Single phase semiconverter is operated from 120 V, 50 Hz ac supply. The load current

with an average value Idcis continues and ripple free firing angle

α=π/6, Determine

(i) Displacement factor

(ii) Harmonic factor of input current

(iii) Input power factor

UNIT – III

DC – DC CONVERTER

PART – A

1. What are the disadvantages of frequency modulation scheme over the pulse-width

modulation scheme.

2. Define the term duty cycle converters of DC chopper

2. What are the methods of controlling the output voltage of a chopper?

3. Give the applications of SMPS.

4. Mention any two disadvantages of frequency modulation control strategy.

5. What are the advantages of ZVS When compared toZCS.

6. What is the principle of current limit control for chopper?

7. What is meant by SMPS & mention it’s two advantages?

8. What is meant by time ratio control in chopper?

9. Write any two salient features of CUK converter.

PART – B

1. Derive the expression for the output voltage of a step-up chopper & explain its control

strategies. (16)

2. Discuss the principle of operation of DC-DC step-down chopper with suitable

waveform. Derive an expression for its averageDC output voltage. (16)

3. A step-up chopper has input voltage 220 V and output voltage of 660 V. if the non-

conducting time of thyristor chopper is 100μs, compute the pulse width of output voltage.

In case pulse width is halved for constant frequency operation, find the new output

voltage. (16)

4. Explain the various modes of operation of BoostDC – DC converter with necessary

waveforms. (16)

5 (a) A DC chopper an input voltage of 200 V and aload of 20Ωresistance. When

chopper is ON, its voltage drop is 1.5 V and the chopping frequency is 10 kHz .If the

duty cycle is 80% .

Find (1) Average output voltage.

(2) RMS output voltage.

(3) Chopper on time.

(12)

(b) Explain about Type – E chopper. (4)

6. Classify the basic topologies of switching regulators and explain th

UNIT – IV

INVERTERS

PART-A

1. List the advantages of Multiple PWM over singlePWM technique.

2. What is current source inverter?

3. Discuss the functioning of three phase voltage source inverter in 120 degree operating

mode.

4. Mention the difference between sinusoidal PWM and modified sinusoidal PWM

techniques.

5. Differentiate between VSI and CSI?

6. What are the advantages of PWM inverter?

7. Compare 180°and 120°mode inverter operation.

8. List the different types of PWM techniques.

PART – B

1. Explain the principle of operation of three phase inverter with 180°conduction mode

With necessary waveforms and circuits. (16)

2. Describe the functioning of three phase voltagesource inverter supplying a balanced star -

connected load in 120°operating mode. (16)

3. (a) Describe any one PWM technique used in inverter in detail.(8)

(b) Explain the working principle of single phase current source inverter. (8)

4. (a) Write short note on series resonant inverter.(8)

(b) Explain how inverter can be controlled using multiple and sine PWM technique. (8)

5. Explain the operation of single phase commutatedcurrent source inverter with R load. (16)

6. Explain, different methods of voltage control adopted in an inverter with suitablewaveforms.

Unit-5

AC – AC voltage Controller

1.List out the different types of Cycloconverter.

2. What is a matrix converter?

3. What is meant by Cycloconverter?

4. Write the Output RMS Voltage of single phase AC

voltage controllers with resistanceload.

5. What is meant by Integral cycle control?

6. For a single phase AC regulators justify how pulse gating is suitable for R load and not for RL load.

PART - B

1. Explain the working principle of multistage sequence control of AC Voltage controller. (16)

2. Explain the principle of single phase to singlephase step down a Cycloconverter with power

circuit and waveforms. (16)

3. Describe the operation of single phase full waveac voltage controller with the help of voltage

and current waveform. Also derive the expression for average value of output voltage.(16)

4. Explain with waveforms the principle of working single phase to single phase step up

Cycloconverter.

5.List the factors that affect the performance of Cycloconverter. (16)