# VTU Question Papers Basic Electronics

# 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)

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

V_{0} – 12 V, Vin – (25 to 35)V, I_{L} = (35 to 55)mA and l_{z} = (25 to 45)mA. (08 Marks)

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

- Sketch the typical input and output characteristics of an NPN transistor and explain the three regions of operation. (08 Marks)
- Calculate and p<j
_{C}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)

- 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)

- Draw sketches to show the basic construction and equivalent circuit of a UJT. Briefly explain the device operation. (06 Marks)
- 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)

- Explain the Barkhausen criterion for oscillation. (05 Marks)
- 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)

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

V_{0} = — (3V] + 4V_{2} + 5V3), given the inputs V_{J}} V_{2}, V3. (08 Marks)

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

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

i) [0.76423_{lo}= [?]_{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)

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

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