B.E. (Third semester) EXAMINATION, JUNE, 2007
(Common for EC/EE/IP Engg.)
Note. (i) Answer all question.
(ii) Total six question are to be attempted.
(iii) There is internal choice within each question.
(iv) Answer off all objective question should be at one place only.
(vi) Assume suitable missing/misprint data if necessary.
1. Attempt any two objective type question from each unit (A- E) . (total 10. Nos. of question are to
(A) Faster switching OFF of a p-n junction :
(a) requires zero current in the reserve direction.
(b) requires averages situation current in the reserve direction.
(c ) requires a large current in the reserve direction.
(d) is independent of the serve current.
(ii) For a MOSFET , the gate current
(a) is negligibly small
(b) increase with increase in drain voltage
(c ) decrease with decrease in drain voltage
(d) is dependent of drain voltage.
(iii) The storage time of a p-n junction :
(a) Decreases with increased reverse bias voltage
(b) Decreases with increased forward bias voltage
(c) increases with increased-bias voltage
(d) is none of the above
(B) (i) Positive feedback is used for :
(a) stabilizing the gain (b)generating oscillations (c)increasing bandwidth
(d) Improving the input and output impedances
(ii) voltage shunt negative feedback amplifier approaches :
(a) ideal voltage amplifier
(b) ideal current to voltage convertor
(c) ideal voltage to current convertor
(d) ideal current amplifier
(iii)The maximum efficiency of a class-B push pull amplifier is :
(a) 25 percent (b)50 percent (c)78.5 percent (d)100 percent
(C) (i) An stable multavibrator has :
(a) one stable state (ii) one quasi- stable state
(c ) two stable state (iv) two quasi- stable state
(ii) CE configuration is the most preferred transistor configuration when used as a switch because :
(a) It require only one power supply
(b) It require low voltage or current for operating the switch
(c ) it is easily understood by everyone
(d) it has small ICEO
(iii) Ideal differential amplifier has a CMRR :
(a) Zero (b) infinity
(c ) 100 (d) 10000
(D) (i) Input offset voltage of an ideal OP-AMP should be :
(i) Low (ii) high
(iii) zero (iv) infinity
(ii) For an inverting amplifier the voltage gain is -10 and the resister at input circuit is 10 k. The feedback resister will be:
(a) 10 k (b) 1 K
(c ) 100 K (d) 1000 K
(iii) The Schmitt trigger circuit behaves as a :
(a) Square wave generator
(b) monostable multavibrator
( c) bistable multavibrator
( d) free running multavibrator.
(E) (i) For producing latching action thruster uses :
(a) internal negative feedback
(b) internal positive feedback
(c ) none of above
(ii) Once latched , the only way to open the SCR is:
(a) reduce its current below holding current
(b) increase its current above holding current
(c ) positive trigger hit the gate input
(d) none of the above
(iii) The only way to close a four layer diode is with :
(a) reducing current (ii) increasing current
(c ) break cover (d) triggering
2. (a) What do you mean by breakdown in a p-n junction ? Distinguish between avalanche and zener
breakdown in a diode.
(b) Explain the working principle of PNP transistor:
Find the transistor current in the circuit of ahead fig. 1.
A silicon transistor with B=100 and ICo = 20n A is under consideration . Repeat if a 2K emitter
resister is added to the circuit comments on the results :
(a) Explain the V-1 characteristics of Zener diode and explain its working as voltage regulator.
(b) In fig.2, the Bdc of silicon transistor is 80. Draw the d.c. load line where is the Q point if RB = 390 K ?
3. (a) Discuss the effect of negative feedback on gain, input impedance and output impedance ,
(b) Sketch circuit of a Wien bridge oscillator . Explain its working .Determine its frequency of
(a) Under what condition does an amplifier function as an oscillator ? Give the example of an oscillator
to be used at (i) low frequency (ii) high frequency
(b) Explain why even harmonics are not present in push pull transistor ? Explain the working of class A
push pull amplifier . Determine its maximum conversion efficiency.
4. (a) What is meant by CMRR ? Derive a relationship of it.
(b) Explain the bitable multavibrator circuit with the help of output waveform. Also give its applications.
(a) Explain the working of transistor as a switch.
(b) Draw the circuit of a differential amplifier and explain its operation . Also discuss the transfer
characteristics of DIFF amplifier.
5. (a) What is 555 timer ? Explain in brief and its applications
(b) Draw the circuit of the following using an op-Amp and explain their operation:
(i) Adder or summering amplifier (ii) Differentiator
(iii) Log amplifier
(a) Explain input bias current , input offset current and slew rate regarding OP-AMP.
(b) Draw the circuit of astable multavibrator using 555 timer. Explain its operation and sketch the
6. (a) Explain the operation and application of the inverter circuit.
(b) Explain V-1 characteristics of SCR. What is meant by Gate ON and OFF times ? Discuss turn OFF
and turn ON mechanism in SCR.
(a) Explain UJT firing circuit.
(b) Write about construction of SCR. Explain different method for starting on SCR.