Anna University

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.

Third Semester

Electronics and Communication Engineering

EC 2205 — ELECTRONIC CIRCUITS — I

(Regulation 2008)

Time : Three hours

Maximum : 100 marks

Answer ALL questions.

PART A — (10 × 2 = 20 marks)

1. What are the types of transistor biasing?

2. Differentiate bias stabilization and compensation techniques.

3. Why are common emitter amplifiers more popular?

4. Determine the output voltage of a differential amplifier for the input voltages of 300 ? V and 240? V. The differential gain of the amplifier is 5000 and the value of the CMRR is 100.

5. Mention the effect of coupling capacitors on the bandwidth of the amplifier.

6. Short circuit common Emitter current gain of transistor is 25 at a frequency of 2 MHz if = 200 ? f KHz. Calculate (a) T f (b) fe h .

7. List the disadvantages of pushpull amplifier.

8. Define Harmonic distortion and intermodulation distortion.

9. Write down the expression for ripple factor of L filter in FWR.

10. Distinguish between line regulation and load regulation.

PART B — (5 × 16 = 80 marks)

11. (a) For a circuit shown in fig. 1, = 20 CC V V, R = k C 2 ? =50 , = 0.2 BE V V, R = 100 k 1 , =100 E R . Calculate B I , CE V , C I and stability factor S . (16)

Or

(b) With the help of neat diagram, explain methods used in biasing the FET and MOSFET. (16)

12. (a) (i) Compare CB, CE and CC amplifiers and their uses. (8)

(ii) Consider a single stage CE amplifier with R = k S1 and R = k L 1.2 . Calculate i A , i R , v A , i A , power gain and o R if h k ie = 1.1 , 4 2.5 10 ? = × re h , =50 fe h and h A V oe = 25 ? / . (8)

Or

(b) Discuss in detail methods of increasing input impedance using Darlington connection and Bootstrapping. (16)

13. (a) Explain in detail with neat diagram frequency response of BJT amplifier. Discuss the significance of cut off frequencies and Bandwidth of the amplifier. (16)

Or

(b) (i) Derive the expression for frequency response of multistage amplifier. (10)

(ii) Discuss the significance of cut off frequencies and Gain bandwidth product of amplifier. (6)

14. (a) A power transistor operated in class A operation delivers a maximum of 5W to a 4 ohms load with the supply voltage of 20 V. The quiescent operating point is adjusted for a symmetrical swing.

Calculate,

(i) Step down turns ratio.

(ii) Peak collector current.

(iii) Co-ordinates of quiescent operating point.

(iv) Efficiency. (16)

Or

(b) Draw the circuit diagram of class B push pull amplifier and discuss its merits. (16)

15. (a) Draw and explain working of Halfwave rectifier circuit. In a half wave rectifier circuit, diode has an internal resistance 20 and 110 V rms source of supply. Calculate

(i) Efficiency of rectification.

(ii) Ripple factor.

(iii) Percentage regulation from no load to full load. (16)

Or

(b) Explain working of

(i) Switched mode power supply. (8)

(ii) Power control using SCR. (8)

Use neat diagrams.