# JNTU Previous Exam Papers B.Tech

# May/Jun 2008

# BASIC ELECTRONIC DEVICES AND CIRCUITS

# SET-3

1. (a) An electron is moving perpendicular to magnetic field ‘B’. Derive the expression for radius ‘R’ of the trajectory and period of rotation T.

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

2. (a) Draw the basic structure of a varactor diode and explain its characteristics.

(b) Write the diode equation and discuss the effect of temperature on diode current.

3. (a) Draw the block diagram of a regulated power supply and explain its operation.

(b) Define line regulation and load regulation. Give their typical numerical values.

4. (a) Draw the circuit and explain the characteristics of BJT (input and output characteristics) in C.E. configuration.

(b) Give the specifications, parameters and typical values of a silicon NPN transistor.

5. (a) Differentiate bias stabilization and compensation techniques.

(b) Design a voltage divider bias network using a supply of 24V, β=110 and ICQ=4μA, VceQ=8V choose Ve=Vcc/8.

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

(b) A transistor used in CE amplifier connection has the following set of h parameters, hie=1KΩ , hfe=100, hre=5×10−4, hoe= 2×10−5

Ω−1 Rs=15KΩ , RL=5kΩ Determine input impedance, output impedance, current gain and voltage gain.

7. (a) An amplifier has a gain of -100 and a distortion of 8%. What is the effect of introducing negative feedback with feedback factor of 0.05?

(b) Find Af for a CE stage with an un bypassed emitter resistor.

8. (a) What is condition of unity loop gain to sustain oscillations? Prove it.

(b) Prove that the ratio of the parallel to series resonant frequencies of a crystal is 1+1/2(C/C’).