# First/Sec Sem B.E. Degree Examination, June July 08

Time: 3 hrs.

Note : Answer any FIVE full questions,

selecting at least TWO questions from each part,

PART-A

1     a. Sketch typical V – I characteristics of a pn junction. Explain the shape of the V – 1

characteristics and identify the important points.    (06 Marks)

1. Draw the circuit of a full wave Bridge Rectifier and show that ripple factor = 0.48 and efficiency = 81%.          (06 Marks)
2. Design a Zener Regulator with the following specifications.

V0 – 12 V, Vin – (25 to 35)V, IL = (35 to 55)mA and lz = (25 to 45)mA. (08 Marks)

2                         a. Show that a transistor can be used as an amplifier. (06 Marks)

1. Sketch the typical input and output characteristics of an NPN transistor and explain the three regions of operation.   (08 Marks)
2. Calculate and p<jC for the transistor if Ic is measured as 1mA and Ib is 25 fiA. Also determine the new base current to give Ic = 5 mA.                                                 (06 Marks)

3                         a. Define biasing of a transistor. Compare the base bias, collector to base bias and voltage

divider bias and discuss the advantages and disadvantages of the three types of bias circuits.                        (10 Marks)

1. Design the voltage divider bias circuit as shown in Fig. Q 3(b).

The bias conditions are to be Vce = 3 V, = 5 V and Ic — 1 mA.

a. Sketch a block diagram to represent an n — channel FET. Indicate voltage and current direction and the device operation.  (06 Marks)

1. Draw sketches to show the basic construction and equivalent circuit of a UJT. Briefly explain the device operation.      (06 Marks)
2. Draw the diagram of an SCR Zero Point triggering circuit. Explain the circuit operation and advantages and draw the load wave form. (08 Marks)

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06ELN15/25

PART-B

a. Sketch the circuit of a two page capacitor coupled, CE amplifier, and explain its working.

(08 Marks)

1. Explain the Barkhausen criterion for oscillation.    (05 Marks)
1. In a Colpitt’s Oscillator, if the desired frequency is 800 kHz, determine the values of L and C.                                                                     (07 Marks)

6                        a. Mention the ideal characteristics of an OP – AMP.   (06 Marks)

1. Explain the working of a CRT.                        (06 Marks)
1. Design a scaling adder circuit using an OP — AMP to give the output –

V0 = — (3V] + 4V2 + 5V3), given the inputs VJ} V2, V3. (08 Marks)

7                         a. Explain the need for modulation.                    (04 Marks)

1. Draw the block diagram of a super heterodyne AM receiver and explain the function of each block.                         (10 Marks)
2. Solve:

i)        [0.76423lo= [?]2

ii)      [AD6CB]]6 = [?]8

iii)    [1101L101 l]2 = [?]s

iv)    Substract using 2’s complement, 66 — 64

v)      Add [24}g to [66]g

vi)    [1011.11001]2 — [?]io-                             (06 Marks)

8                        a. i) Prove that

AB + A + AB = 0 ii) Simplify

XYZ + XYZ + XY + XY.                                                                                                                              (03 Marks)

1. Draw the logic circuit for Full Adder and write its truth table with expression. (08 Marks)
2. Explain how AND, OR and NOT gates can be obtained using only NAND gates. (09 Marks)

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