Code: A-05                                                                                Subject: BASIC ELECTRONICS

Time: 3 Hours                       Flowchart: Alternate Process: December 2005                                                                              Max. Marks: 100

 

NOTE: There are 9 Questions in all.

·      Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

·      Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

·      Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

                

a.       The current amplification factor in CE configuration is  

 

                   (A)  .                                               (B)  .

(C)    .                                           (D)  .

                

b.      A zener diode

 

(A)    has a high forward voltage rating. 

(B)    has a sharp breakdown at low reverse voltage.

(C)    is useful as an amplifier.                

(D)    has a negative resistance.

            

             c.   N-channel FETs are superior to P-channel FETs, because

                        

(A)    they have a higher input impedance.   

(B)    they have high switching time.

(C)    they consume less power.

(D)    mobility of electrons is greater than that of holes.

 

             d.   The maximum possible collector circuit efficiency of an ideal class A power amplifier is

 

(A)    15%.                                          (B) 25%.

(C)  50%.                                           (D) 75%.  

 

             e.   Negative feedback in an amplifier

                                      

(A)     reduces the voltage gain.              

(B)     increases the voltage gain.

(C)     does not affect the voltage gain.         

(D)    converts the amplifier into an oscillator.

 

             f.    For generating 1kHz signal, the most suitable circuit is

 

(A)     Colpitts oscillator.                        (B)  Hartley oscillator.

(C)  Tuned collector oscillator.             (D)  Wien bridge oscillator.

 

             g.   The output stage of an op-amp is usually a

 

(A)     complementary emitter follower.  

(B)     transformer coupled class B amplifier.

(C)     class A power amplifier.

(D)    class B amplifier.                         

 

             h.   When a sinusoidal voltage wave is fed to a Schmitt trigger, the output will be

 

(A)    triangular wave.                            (B) asymmetric square wave.

(C) rectangular wave.                          (D) trapezoidal wave.

 

             i.    If the peak value of the input voltage to a half wave rectifier is 28.28 volts and no filter is used, the maximum dc voltage across the load will be

 

(A)   .                                    (B) 15 V.

(C) 9 V.                                              (D) 14.14 V.

 

             j.    The logic gate which detects equality of two bits is

 

(A)  EX-OR.                                       (B)  EX-NOR.

(C)  NOR.                                          (D) NAND.

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

  Q.2     a.   Explain how Hall effect may be used to measure mobility of charge carries in semiconductors.                                                                    (7)

                

             b.   Distinguish between avalanche and zener breakdown in p-n junction diode.         (7)

 

             c.   A BJT has a base current of 250  and emitter current of 15 mA.  Determine the collector current and .                                                           (2)

 

  Q.3     a.   Draw the circuit of Darlington amplifier and analyse it to obtain expressions for its current gain and input impedance.  Also mention its merits and applications.                                                        (10)

 

             b.   In the circuit shown in Fig.1, .  Find the quiescent values of ,  and  of the FET.                                              (6)                                                             

 
 

 

 

 

 

 

 



  Q.4     a.   In the transformer coupled class A amplifier shown in Fig.2 below, the transistor has  and .  Assume that the transformer is ideal and that  and also .  Determine values of and  to obtain quiescent current .  If the collector current swing is , find the peak values of load current and load voltage.  Transformer turns ratio is primary 1 : 6 secondary.                                                           (10)
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


             b.   Draw the circuit of common source amplifier using JFET and show its equivalent circuit.  Analyse the equivalent circuit to find an expression for voltage gain and output resistance.                      (6)

 

  Q.5     a.   For an amplifier having open loop gain A, find an expression for gain with negative feedback of feedback ratio.  Show how stabilization of gain of an amplifier is achieved with negative feedback. (6)

                

             b.   A negative feedback of  is applied to an amplifier of open loop gain 1000.  Calculate the change in overall gain of the feedback amplifier if the gain of the internal amplifier is reduced by 20%.                                                            (4)

 

             c.   Show an FET source follower circuit.  What type of negative feedback takes place in the circuit?  Analyse the circuit to derive an expression for voltage gain with feedback.                                       (6)

 

  Q.6     a.   Explain the principle underlying the working of R-C oscillators.  Mention the applications of R-C oscillators.                                                                                                                         (7)

 

             b.   Draw the circuit of sample and hold using op-amp and explain its operation.                       (9)

 

  Q.7     a.   Write a neat circuit diagram of saw-tooth wave generator using op-amps and describe its operation.  Derive an expression for the frequency of the wave.                                                                      (10)   

 

             b.   Explain how an astable multivibrator can be implemented using 555 timer IC.                      (6)

 

  Q.8     a.   Why filters are used along with rectifiers in the construction of a power supply?  List the filter types used in power supplies.  Explain their effect on rectifier output waveforms.                                     (10)

 

             b.   A full wave rectifier is fed with a voltage, 50 sin 100 .  Its load resistance is .  The diodes used in the rectifier have an average forward resistance of .  Compute the

(i)                  average and rms values of load current .

(ii)                ripple factor and

(iii)               efficiency of rectification.                                                            (6)

 

  Q.9     a.   Delineate the concept of ‘duality’ in Boolean Algebra.                                         (3)

 

             b.   For the function, , write the canonical POS and SOP expressions.             (2)

 

             c.   Write the logic diagram of a clocked R-S flip-flop using only NAND gates.  Explain its operation with reference to truth table.                        (6)

 

             d.   Write the truth table for full adder and show its implementation using gates.                         (5)