Answer Question No .1 which carries 14 marks and any

FOUR from the remaining questions

All questions carry equal marks

  1. (a)  Distinguish between Avalanche and zener break downs.

(b)  Explain why does a transistor need biasing.

(c)   Explain the tunneling phenomenon

(d)   Draw the circuit diagram of a transistor in CB configuration.

(e)   The field effect transistor is a voltage sensitive electronic control device. Explain why is the case?

(f)   Give the principle behind the varactor diode.

(g)   What is a  MOSFET? Why are N-channel MOSFETs preferred row  -Pchannel MOSFETs?

2. (a) Explain drift and diffusion phenomenon in semi conductor. Derive an expression for the electron current due to drift and diffusion.

(b) In a N-type semi conductor, the Fermi level lies  0.4 ev below the conduction band at 300K . Determine the new position of the Fermi level if

(1)  The temperature is increased to 400K and

(2)  The concentration of donor atoms is increased by a factor of 6. Assume KT = 0.003 eV

3.  (a)  Explain the principle of operation of a p-n diode and explain how a diode can act as a rectifier.

(b)  The current through a P-N junction silicon diode is 60 mA at a forward bias voltage of 0.95 V. Calculate the a.c and d.c resistances of 27 ° C.

4. (a)  Explain the construction and the principle of an SCR. Sketch its V-I  characteristics . List its applications.

(b) Explain the terms :

(1)  Peak point voltage Vp and

(2)  Valley point voltage Vv of a UJT.

(c)  Explain the structure and V-I characteristics of zener diode and mention its applications.

5.  (a)  Derive the relation between α  and  β in a transistor why does the CE configuration provide large  current amplification while the CB configuration does not?

(b) Calculate the values if If  and Ie  for  a transistor with  αd.c=0.99 and ICBO = 5 µA. Iβ  is measured  as 20 μA.

6.  (a)  With the help of neat sketches  and characteristic curves, explain the operation of the junction FET.

(b) How do a MOSFET differ from a JFET? Explain the operation of a depletion mode MOSFET with the help of its drain and gate V-I characteristics.

7.  (a)  Derive an expression for single phase full wave rectifier efficiency, form factor , ripple factor and average output voltage without filter and simple C-filter.

(b)  A 15-0-15 volts (r.m.s) ideal transformer is used with a full wave rectifier circuit with diodes having forward voltage drop of 1volt. The load is a resistance of 100 ohms and a capacitor of 0.01 farad is used as a filter across the load resistance . Calculate the load current , voltage and ripple factor.

8.  (a)  Discuss in detail, the transistor self biasing circuit and also compare its behavior with fixed bias circuit.

(b) Explain the method of drawing load line for self-bias transistor circuit characteristic and also explain how bias curve is used to obtain the quiescent point for this curve.

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Answer Question No .1 which carries 14 marks and any FOUR from the remaining questions All questions carry equal marks (a)  Distinguish between Avalanche and zener break downs. (b)  Explain why does a transistor need biasing. (c)   Explain the tunneling phenomenon (d)   Draw the circuit diagram of a transistor in CB configuration. (e)   The field effect...