R09 - December, 2011 - Regular Examinations - Set - 3.

B.Tech II Year - I Semester Examinations, December 2011
ELECTRONIC DEVICES AND CIRCUITS
(COMMON TO EEE, ECE, CSE, EIE, BME, IT, MCT, E.COMP.E, ETM, ICE)
Time: 3 hours Max. Marks: 75
Answer any five questions
All questions carry equal marks
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1.a) With the help of necessary sketches explain the potential distribution in an open circuited PN junction.
b) With the help of V-I Characteristics, explain the operation of a PN Diode under Forward bias and Reverse bias. [7 8]
2.a) With neat sketches explain the operation of a FWR with shunt capacitor filter & Derive the expression for its ripple factor.
b) A bridge rectifier uses four identical diodes having forward resistance of 5O each. Transformer secondary resistance is 5 ohms and the secondary voltage is 30V (rms). Determine the dc output voltage for Idc = 200 mA and value of the output ripple voltage. [7 8]
3.a) Draw the circuit diagram of NPN transistor in Common Base (CB) configuration. With neat sketches and necessary equations, describe its static input- output characteristics and clearly indicate the cut-off, saturation & active regions on the output characteristics?
b) With reference to a BJT, define the following terms and explain:
i) Emitter efficiency.
ii) Base transportation factor.
iii) Large signal current gain. [9 6]
4.a) Obtain the condition for thermal stability of a BJT used in a biasing circuit?
b) Design a self bias circuit using silicon transistor to achieve a stability factor of 10, with the following specifications: VCC = 16V, VBE = 0.7V, VCEQ = 8V, ICQ = 4 mA & ß= 50. [5 10]
5.a) Draw the circuit diagram & small signal equivalent circuit of CE amplifier using accurate h-parameter model. Derive expressions for AV, AI, Ri & R0.
b) A bipolar junction transistor with hie = 1100O, hfe = 50, hre = 2.4x10-4, hoe = 25 µA/V, is to drive a load of 1KO in Emitter-Follower arrangement. Estimate AV, AI, Ri & R0? [8 7]
6.a) With the help of neat sketches and characteristic curves explain the construction & operation of a JFET and mark the regions of operation on the characteristics?
b) Show that in Field Effect Transistor, the transconductance, gm = gmo [1- VGS/ Vp]
[8 7]

7.a) Draw the basic structure and equivalent circuit of UJT. Explain how the UJT can be used as a negative-resistance device with the aid of static characteristics.
b) In the common source FET amplifier shown in Figure.1, the transconductance and drain dynamic resistance of the FET are 5mA/V and 1MO respectively. Estimate AV, Ri & R0?
Figure.1
8.a) With neat sketches and necessary expressions describe V-I characteristics of a semiconductor photo diode?
b) With neat sketches and necessary expressions describe the operation of Varactor diode? [8 7]
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