## Download Previous Year PTU University Question Paper of Power Electronics BTEE-504 5th Sem Batch 2011 Onwards B.Tech PTU April 2019 Question Paper

**B.Tech.** **(EE-2011 Batch)**

## POWER ELECTRONICS

### Subject Code : BTEE-504 Paper ID : [ 70557]

### Time : 3 Hrs. Max. Marks : 60

#### INSTRUCTIONS TO CANDIDATES :

1. SECTION-A is COMPULSORY consisting of TEN questions carrying TWO marks each.

2. SECTION-B contains FIVE questions carrying FIVE marks each and students have to attempt any FOUR questions.

3. SECTION-C contains THREE questions carrying TEN marks each and students have to attempt any TWO questions

## Power Electronics BTEE-504 5th Sem Batch 2011 Onwards B.Tech PTU April 2019 Question Paper

**SECTION-A**

**Q1. Answer Briefly.**

#### a) Differentiate between holding and latching current in a Thyristor.

#### b) What is the role of dv/dt in the operation of a Thyristor?

#### c) Differentiate between Diac and Triac.

#### d) What is the function of free wheeling diode?

#### e) What is a LASCR?

#### f) Write applications of a Thyristors.

#### g) What is the importance of Surge current rating of a Thyristor?

#### h) Draw turn on characteristics of a Thyristor.

#### i) Draw snubber circuit.

#### j) What is duty cycle of a chopper?

## ** SECTION-B**

**Q2. Attempt any FOUR questions. 5×4=20**

#### Q2 Explain two transistor model of a Thyristor.

Q3 Compare power MOSFETs with BJTs.

Q4 Discuss operation of single phase mid-point cycloconverter with R-L load for continuous conduction with relevant circuit diagram and necessary output waveforms.

Q5 Describe the working of step down chopper and derive expression for output voltage.

Q6 Draw and explain the simple SCR series inverter circuit employing class A type commutation with the help of important waveforms. State the limitations of this inverter.

** SECTION-C**

**Q3. Attempt any TWO questions.**** 2×10=20**

#### Q7 What are the methods for voltage control within the inverters? Explain in detail with waveforms.

#### Q8 a) Define string efficiency for series /parallel connected SCRs .Show the string efficiency of two series connected SCRs is less than one.

#### b) Explain the difference between class A and class B commutation.

#### Q9 A 230 V, 50 Hz, one pulse SCR controlled converter is triggered at a firing angle of 40° and the load current extinguishes at an angle of 210°. Find the current turn off time, average output voltage and average load current for

#### a) R = 5 ohm and L = 2 mH.

#### b) R = 5 ohm, L = 2 mH and E = 110 V.

Holding and latching current in a Thyristor.

Role of dv/dt in the operation of a Thyristor.

Differentiate between Diac and Triac.

Function of free wheeling diode.

LASCR.

Applications of a Thyristors.

Importance of Surge current rating of a Thyristor.

Characteristics of a Thyristor.

Snubber circuit.

Duty cycle of a chopper.

##### Power Electronics BTEE-504 5th Sem Batch 2011 PTU April 2019 Paper

Two transistor model of a Thyristor.

Compare power MOSFETs with BJTs.

Circuit Diagram of Single phase mid-point cycloconverter with R-L load for continuous conduction

Working of step down chopper and derive expression for output voltage.

Simple SCR series inverter circuit employing class A type commutation.

State the limitations of this inverter.

##### Power System-1 4th Sem Batch 2011 B.Tech PTU April 2013 Question Paper

Methods for voltage control within the inverters.

String efficiency for series /parallel connected SCRs .

Show the string efficiency of two series connected SCRs is less than one.

Difference between class A and class B commutation.

230 V, 50 Hz, one pulse SCR controlled converter is triggered at a firing angle of 40° and the load current extinguishes at an angle of 210°. Find the current turn off time, average output voltage and average load current for

a) R = 5 ohm and L = 2 mH.

b) R = 5 ohm, L = 2 mH and E = 110 V.