# GTU previous question papers -BE- VII Sem -Power Electronics -Nov/Dec-2011

GTU previous question papers

GUJARAT TECHNOLOGICAL UNIVERSITY

BE SEM-VII Examination-Nov/Dec.-2011

Subject code: 171002

Subject Name: Power Electronics

Instructions:

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

Q.1 (a) Give classification of thyristor family. Draw and explain SCR in detail. Also draw and explain SCR V-I characteristics with required terms.

(b) What is GTO ? Draw and Explain GTO structures . Also explain GTO Turn off mechanism with desired equation and figures.

Q.2 (a) List all SCR triggering circuits and explain any two of them in detail using circuit diagram, Waveforms and equations.

(b) Draw and explain construction of power BJT. Also explain I-V characteristics of power BJT. How power BJT are differed then

normal BJT.

OR

(b) Draw and explain the structure of power MOSFET. Also explain principle of operation and I-V characteristics of power MOSFET

Q.3 (a) Draw and Explain Full wave controlled rectifier with the inductive load using required waveforms and equations. Also explain use and function of free wheeling diode with the inductive load.

(b) An SCR with latching current of 100 mA is connected with series resistance of 10 ῼ and inductance of 1H. DC source voltage is 2          V. calculate minimum gate pulse width to turn ON SCR.

OR

Q.3 (a) Draw and explain Three Phase Half wave controlled rectifier with required waveforms and equations

(b) A 3 Phase bridge circuit is supplied by 200 V .Assume continuous load current. Determine mean load voltage at firing angle 00 ,450 ,900 Neglect all devices drops .If commutating diode is placed across the load then what will be the mean load voltage at ∞ = 1200 .

Q.4 (a) Classify the chopper. List all types of Chopper and explain any two of them.

(b) In a step UP chopper applied voltage is 200V and O/P voltage is 600V . If conducting time of thyristor is 200μSec Compute

(a) Chopper frequency

(b) Find O/P voltage for when pulse width is half for constant

frequency of operation.

OR

Q.4 (a) Draw and explain Full bridge invertors. Also give comparison of Half bridge and Full bridge Inverter

(b) A 3 Phase bridge inverter operating in a 1800 mode with a wye connected resistive load . If supply voltage is 230 V Find the rms

phase voltage.

Q.5 (a) What is UPS / Why we need that ? Draw and explain Online UPS system with their operation and features

(b) List types of Heating mechanism available and explain any one of them in detail.

OR

Q.5 (a) What is SMPS ? Give classification of SMPS. Also explain any one of the SMPS.

(b) Draw the circuit diagram of a Battery charging Regulator and Explain them in detail.