M.Sc. (Semester IV) (CBCS) Examination Mar/Apr-2018
Electronics Science
POWER ELECTRONICS
Time: 2½ Hours
Max. Marks: 70
Instructions: Q. and are compulsory. Answer any three questions from Q.3 to Q.7. All questions carry equal marks. Use of nonprogrammable calculator is allowed.
Q.1
Select the most correct alternative.
14
SMPS is used for
Obtaining regulated ac power supply
Obtaining regulated dc power supply
Storage of dc power
Switch from one source to another
SMPS can be used as an
AC to DC converter, for use in many mains powered circuits,
DC to DC converter
Both a and b
None of these
The class A commutation or load commutation is possible in case of
DC circuits only
AC circuits only
Both DC and AC circuits
None of the above mentioned
An SCR is usually turned on by
Break over
A gate trigger
Latching current
Holding current
Thyristor can be protected from over voltages by using
voltage clamping device
fuse
heat sink
snubber circuit
The converter is used in SMPS circuits where the DC output voltage needs to be higher than the DC input voltage.
Buck
Cük
Boost
Buck-Boost
A thyristor is a
device
device
device
P-N device
di/dt protection is provided to the thryistor by
Connecting an inductor in parallel across the load
Connecting an inductor in series with the load
Connecting an inductor in parallel across the gate terminal
Connecting an inductor in series with the gate
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SLR-UH-313
The local hot spot formation in the cross-section of the SCR is avoided by
reducing the junction temperature
applying gate current nearer to the maximum gate current
using only r loads
proper mounting of the scr on heat sink
10) DC choppers converts
AC to DC
DC to AC
DC to DC
AC to AC
11) A triac is a switch.
Bidirectional
Unidirectional
Mechanical
None of these
12) For a single phase thyristor circuit with R load firing angle the conduction angle can be given by




13) In the principle of phase control,
the load is on for some cycles and off for some cycles
control is achieved by adjusting the firing angle of the devices
control is achieved by adjusting the number of on off cycles
control cannot be achieved
14) Which is the disadvantage of an ac voltage controller?
High efficiency
Flexibility in control
Less maintenance
Harmonics in the supply current
Q.2
Attempt the following.
14
Discuss the complex characteristics of an SCR.
05
What are the different methods to turn on the thyristor?
04
What is meant by SMPS? What are different types of SMPS
05
Q.3
Explain in detail SCR with its relevant diagrams.
10
What is a snubber circuit?
04
Q.4
What is a forced commutation? Explain class A and B forced commutation techniques of thyristor in detail.
10
What is meant by di/dt protection?
04
Q.5
Describe the working principle of a boost regulator with relevant waveforms.
10
Compare: SMPS with conventional power supply.
04
Q.6
Draw and explain the single phase half controlled bridge rectifier with R and RL load.
10
Freewheeling diode improves the load current waveform Comment.
04
Q.7
Draw and explain the single phase half wave controller with R and RL load.
10
What is an ON-OFF control?
04