# JNTU Exam Papers B-Tech

# Basic Electronic Devices and Circuits

# May/Jun-2008 Set-I

1. (a) Derive the expressions for acceleration, Velocity and displacement of a charged particle placed in an electric field E.

(b) Two parallel plates of a capacitor are separated by 4 cms. An electron is at rest initally at the bottom plate. Voltage is applied between the plates, which increases linearly from 0V to 8V in 0.1 m.sec. If the top plate is +ve, determine:

i. The speed of electron in 40 n sec

ii. The distance traversed by the electron in 40 n sec.

2. (a) What are the various applications of p-n junction diode? Explain them.

(b) What are the specifications of p-n junction diode? Explain how reverse saturation current varies with temperature both in Si and

Ge diodes.

(c) Explain about the characteristics of zener diode.

3. (a) A 15-0-15 Volts (rms) ideal transformer is used with a full wave rectifier circuit with diodes having forward drop of 1 volt. The load is a resistance of 100ohm and a capacitor of 10,000?f is used as a filter across the load resistance. Calculate the dc load current and voltage.

(b) Explain the working of the Half wave rectifier circuit with neat sketch of waveforms at various points in the circuit.

4. (a) A transistor operating in CB configuration has IC = 2.98 mA, IE = 3.00mA and ICO=0.01 mA what current will flow in the collector circuit of this transistor when connected in CE configuration with a base current of 30 ?A.

(b) The reverse saturation current in a transistor is 8?A. If the transistor common base current gain is 0.979, calculate the collector and emitter current for 40 ?A base current.

5. (a) Compare the advantages and disadvantages of biasing schemes.

(b) Calculate the quiescent current and voltage of collector to base bias arrange-

ment using the following data:

Vcc =10V, Rb=100K, Rc=2K, ?=50 and also specify a value of Rb so that Vce=7V.

6. (a) A transistor used in CB circuit has the following set of h parameters, hib=20, hfb=0.98, hrb=3×10?4, hob= 0.5×10?6. Find the values of Ri, Ro, Ai and Avif Rs =600 and RL=1.5K

(b) Draw the small signal hybrid model of CE amplifier and derive the expressions for its Ai, Av, Ri and Ro.

7. (a) The output impedance may be calculated as the ratio of the open circuit voltage to the short circuit current. Using this method evaluate output resistance with feedback Rof for a current-series feedback amplifier.

(b) Draw an emitter follower circuit diagram and find the feedback factor and the input resistance with feed back.

8. (a) Prove that the frequency stability improves as d?/dw increases in oscillators.

(b) Draw the FET crystal oscillator and derive the equation for frequency of oscillations.