GRUP:- A
(1) The number of doped regions of SCR is
(a) 2. (b) 4 (c) 5 (d) 6(2) A thyristor is reverse biased. A positive gate pulse is applied. The thyristor:
(a) Wil be turned on
(b) May or may not turn on
(c) Will not turn on
(d) Will turn on after sometime
(3) A thyristor needs protection against:
(a) High di/dt
(b) High dv/dt
(c) Both high dv/dt and high di/dt
(d) Either high dv/dt or high di/dt
(4) Which of these commutation methods uses
an auxiliary SCR?
(a) Class A
(b) Class B
(c) Class C.
(d) Class D
(5) A single phase half wave converters feeding a resistive load, Just before triggering the
Voltage across thyristor is :
(a) Zero
(b) About 1V
(c) Same as the input voltage
(d) Twice the input voltage
(6)In an SCR, the anode current is controlled by:
(a) Gate currents only,
(b) External circuit only
(c) Both gate current and external circuit
(d) None of the above
(7) A single phase half wave rectiher circuit has a free wheeling diode. The free wheeling
diode will conduct only if:
(a) Load is purely resistive
(b) Load 1s purely inductive.
(c) Load is combination on of R and L
(d) Load is purely inductive or combination of R & L
(8) If tON and tOEF are the turn ON and turn OFF times of a thysistor, then:
(a) toN and tOFF are almost equal
(b) tON >> tOFF
(c) tOFF >> tON
(d) tON is about twice of tOFF
(9) The device commonly used for triggering a TRIAC is :
(a) Diode
(b) Transistor
(c) Zener diode
(d) DIAC
(10)A transistor is said to be useful to be configured as an amplifier when its β is (a) Less than 0
(b) Between 0 and 1
(C) Between I and 50
(d) Greater than fifty
(11) which one of the following is the main
advantages of SMPS over linear power
supply?
(a) No transformer is required
(b) Only one stage of conversion
(c) No filter is required
(d) Low power dissipation
(12) This is an example of the output swing for a class....amplifier.
(a) A
(b) B
(c) AB
(d) C or D
(13) In a step down chopper using pulse width modulation ToN =3 x 10 s and ToFFI X 10 s. The Chopping frequency
(a) 333.33Hz
(b) 250 Hz
(c) 500 Hz
(d) 1000 Hz
(14) which amplifier is commonly used as a frequency multiplier?
(a) Class A
(b) Class B
(c) Class C
(d) All of the above
(15) A Single phase half wave circuit has Vs 230V With a R load of 100 ohm. Find the average load current at α= 30°
(a) 1.45 A
(b) 0.57 A
(c) 0.96A
(d) 2.3 A
(16) A dual converters has:
(a) Two full converter in series
(b) Two full converter in parallel
(c) Two full converter in antiparallel
(d) Two half converters in seriesS.
(17) For a setup chopper, if duty cycle α = 0.5 then
(a) Vo= Vs
(b) Vo < Vs
(c) Vo> Vs
(d) None of these
(18) In an UJT with VBB as the voltage across
two base terminal, the emitter potential at
peak point is given by:
(a) η VBB
(b) ηVp
(c) ηVBB+Vp
(d) ηVp+VBB
(19) A step-down chopper is also called a:
(a) First -quadrant chopper
(b) Second -quadrant chopper
(c) Third-quadrant chopper
(d) Fourth -quadrant chopper
(20)SMPS are based on the ... principle.
(a) Phase control
(b) Integral control
(c) Chopper
(d) MOSFET
GROUP:- B
Each question carries 4 marks:-
2. How an scr can be triggered by gate signal ? Explain.
Or
Define voltage regulation. The d.c. output voltage is 400V with no load and decreases to 300V at full load. Find the voltage regulation.
3.What is harmonic distortion in an amplifier?
Explain.
Discuss the different turn ON mechanisms of SCR s.
4 .Describe the operation of a single phase fully controlled bridge rectifier in brief.
OR
Explain the operation of Push-pull amplifier in brief.
5. In thysistors why commutation is neccssary?Discuss the use of natural communication method used in Thysistorized devices.
OR
Explain the time ratio control (TRC) in d.c. chopper?Also draw the waveforms.
6. (a) Write the application of class-C amplifieres.
(b) Define switching mode regulators.
OR
Write a short note on d.c. motor drIve.
GROUP - C
Answer all Five Questions
7. Define the following terms with reference to an SCR.
(i) Break over voltage
(ii) Holding current
(iii) Latching current
OR
Discuss the operation and V-I characteristic of a thyristor with neat sketch.
8. Describe the working of UJT relaxation oscillator. Also draw the V-I characteristic.
OR
Deseribe the operation of a single phase half controller rectifier with inductive load. Draw the waveform for α = 30°
9. How does a step down chopper work ? Explain.
OR
A chopper is supplied with 230V d.c. mains and remains ON for 25ms. It remains OFF for 1Oms in each cycle. Find the average load voltage. Discuss which type of chopper is this?
10. (a) Explain, What is a cycloconverter. Draw the circuit diagram.
(b) Write the differences between buck and boost regulators.
OR
Explain the working of an UPS with a neat block diagram.
11. In a single phase full wave controlled rectifier the supply voltage is 23OV (r.m.s.), 50Hz. The load resistance R =15 Q and if a = n/2. Find
i) The r.m.s value of load voltage
(ii) The load power and
(iii) r.m.S. value of load current.
OR
What are the line commutated inverters?
How do they operate?
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