*8229*
8229
(Pages : 3)
Reg. No. : ..................................... Name : ..........................................
Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) Branch : Electronics and Communication Engineering 08.305 : ELECTRONICS CIRCUITS I (T) Time : 3 Hours
Max. Marks : 100 PART – A
Answer all questions. Each question carries 4 marks. 1. With schematic explain a Zener diode voltage regulator. 2. Derive expression for rise time of a low pass RC circuit. 3. Draw the output waveform and transfer characteristics of the following circuit.
4. Explain the need for biasing a transistor when used as an amplifier. 5. What is body effect in MOSFET ? 6. An FET source follower circuit uses an FET having gm = 2mS and rd = 50 K. The source resistance Rs = 1 K. Find the voltage gain and output resistance. P.T.O.
8229
-2-
*8229*
7. Define parameters f β and f T of a transistor. 8. Explain the biasing circuit used in class AB amplifier. 9. Derive expression for TUF of a full wave bridge rectifier. 10. A class-A series fed power amplifier is required to deliver a maximum power of 20 W to a load of 8 Ω . Calculate the required power supply voltage. (10×4=40 Marks) PART – B Answer any 2 questions from each Module. Module – I 11. Derive expression for ripple factor of full wave rectifier with Π section filter. 12. Derive the response of a high pass RC circuit to square wave input. Explain how the circuit functions as differentiator. 13. Determine the transfer characteristics for the circuit shown assuming that the diodes are ideal. Plot Vo against Vi for the range of Vi from 0 to 50V.
(2×10=20 Marks)
*8229*
-3-
8229
Module – II 14. a) What is thermal runaway ? How it can be avoided ? b) For a fixed circuit, Vcc = 10 V, RB = 50 K and R C = 500 Ω . Assume silicon transistor with β = 50 and VBE = 0.7 V. Find the co-ordinates of the Q-point. Draw the dc load line and locate the Q-point. 15. Using low freq. model, derive expression for AI, AV and Z i of an emitter follower circuit. 16. Derive expression for voltage gain and output resistance of a common source amplifier without source bypass capacitor. (2×10=20 Marks) Module – III 17. Using hybrid- π model, derive expression for short circuit current gain of a common emitter amplifier. 18. Explain the operation of a Class- β push pull amplifier . Derive expression for conversion efficiency. 19. The following low frequency parameters are known for a given transistor at room temperature (300 K) at I C = 10 mA and VCE = 8 V. hie = 500 Ω , hoe = 2×10–4 μs, hfe = 100 and hre = 10–4. At the same operating point f T = 50 MHz and Cc= 3pF. Calculate the values of hybrid- π parameters. (2×10=20 Marks)
__________________________