CLASS: B.Sc. ELECTRONICS
11N/ 193
St. JOSEPH’S COLLEGE (AUTONOMOUS) TIRUCHIRAPPALLI – 620 002
SEMESTER EXAMINATIONS – NOVEMBER 2011
TIME: 3 Hrs.
MAXIMUM MARKS: 100
SEM
SET
PAPER CODE
TITLE OF THE PAPER
V
2009
08UEL530302A
CORE ELECTIVE : POWER ELECTRONICS
SECTION – A
Answer all the questions:
20 x 1 = 20
Choose the correct answer:
1.
MOSFET is a ______
a) Current driven device
c) Low input impedance device
b)
d)
Voltage driven device
a power driven device
2.
To turn off a SCR, it is necessary to reduce its current less than _______
a) trigger current
b) Holding current
c) Break over current
d) None of the above
3.
In a single phase half wave rectifier, the average output voltage is given as
a)
b)
1 
1 
 Vm cos wt dwt
c)
4.
 
1 
 Vm sin wt dwt
2 
 Vm sin t cos t dt
d)
2 
1 
 Vm cos wt dwt
2 
The method of commutation, in an inverter is _______
a) line commutation
b) Forced commutation
c) Natural commutation
d) none of above
5.
In a single phase AC voltage controller, the firing angles in the two half cycles ______
a) are always equal
b) are sometimes equal
c) are never equal
d) may be equal (or) unequal
Fill in the blanks:
6.
The base region in a BJT is very ______.
7.
The most commonly used method for triggering a SCR is _____.
8.
In a single phase half wave rectifier, the maximum period of conduction of SCR is ______.
9.
A step up cyclo converter uses ______ commutation.
10.
Static circuit breakers are of two types ______ and ______.
State True or False:
11.
Power diodes are uncontrolled devices.
12.
To turn off GTO, negative pulse is applied between the gate and cathode.
13.
Rectifier is a DC-DC converter.
14.
Cyclo converter is a frequency changer.
15.
AC voltage controllers convert fixed alternating voltage directly to variable alternating voltage
with a change in the frequency.
Match the following:
16.
MOSFET
-
a) ON / OFF control
17.
Thyristor protection
-
b) High frequency operation
18.
DC chopper
-
c) di/dt, dv/dt
19.
Chopper control techniques
-
d) DC-DC converter
20.
Integral cycle control
-
e) PWM control, constant frequency control
SECTION – B
Answer all the questions:
21.
a.
5 x 4 = 20
Explain V-I characteristics of power diode.
OR
22.
b.
Write short notes on MCT.
a.
Explain any two Turn-ON methods of thyristor.
OR
23.
b.
Why protection circuit is necessary for thyristor. Explain the effect of di/dt and dv/dt.
a.
Describe the effect of freewheeling diode in half wave rectifier with RL load.
OR
24.
b.
Calculate the average voltage and RMS voltage for a half wave rectifier with RL load.
a.
Write short notes on (i) TRC (ii) CLC
OR
b.
Explain the operation of single phase voltage source inverter.
25.
a.
Explain shortly about integral cycle control.
OR
b.
Give some advantages of static switches.
SECTION – C
Answer any FOUR questions:
4 x 15 = 60
26.
Explain the operation of power MOSFET with neat diagram.
27.
(i) Describe the different modes of operation of a thyristor with the
characteristics.
(8)
(ii) Discuss the two transistor model of a thyristor.
help of its static V.I
(7)
28.
Describe the working of a single phase half wave rectifier with RLE load.
29.
What is a cycloconverter? Enumerate some of its industrial applications. Describe the
operating principle of single phase step up cycloconverter with neat wave form.
30.
What is SMPS? List the various types of SMPS. Describe any one type of SMPS.
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