BASIC ELECTRONIC DEVICES AND CIRCUITS JNTU UNIVERSITY PREVIOUS YEAR QUESTION PAPER COLLECTION

BASIC ELECTRONIC DEVICES AND CIRCUITS JNTU UNIVERSITY PREVIOUS YEAR QUESTION PAPER COLLECTION

I B.Tech Regular Examinations, May/Jun 2008

BASIC ELECTRONIC DEVICES AND CIRCUITS

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Derive the expressions for acceleration, Velocity and displacement of a chargedparticle 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. [8+8]

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 satu-

ration current varies with temperature both in Si and Ge diodes.

(c) Explain about the characteristics of zener diode. [5+6+5]

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 10,000µf is used as a filter across the load resistance. Cal-

culate 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. [8+8]

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 µA.

(b) The reverse saturation current in a transistor is 8µA. If the transistor common

base current gain is 0.979, calculate the collector and emitter current for 40

µA base current. [8+8]

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

, β=50 and also specify a value of Rb so that

Vce=7V. [8+8]

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 Av

if Rs =600

and RL=1.5K

.

1 of 2

Code No: 07A10401 Set No. 1

(b) Draw the small signal hybrid model of CE amplifier and derive the expressions

for its Ai, Av, Ri and Ro. [8+8]

7. (a) The output impedance may be calculated as the ratio of the open circuit volt-

age 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+8]

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

(b) Draw the FET crystal oscillator and derive the equation for frequency of os-

cillations. [8+8]

I B.Tech Regular Examinations, May/Jun 2008

BASIC ELECTRONIC DEVICES AND CIRCUITS

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

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

(b) Derive the expression for the electro magnetic deflection sensitivity in the case

of hte CRT. [8+8]

2. (a) How does the reverse sturation current of diode varies with temperature. Ex-

plain.

(b) Draw the energy band diagram of p-n diode for no bias, forward bias and

reverse bias and explain. [6+10]

3. (a) Define the following terms of a half wave rectifier with resistive load:

i. Ripple factor

ii. Peak inverse voltage

iii. Rectification efficiency.

(b) A 230 V, 60Hz voltage is applied to the primary of a 5 : 1 step down, center

tapped transformer used in a full wave rectifier having a load of 900

. If the

diode resistance and the secondary coil resistance together has a resistance of

100

, determine:

i. dc voltage across the load

ii. dc current flowing through the load

iii. dc power delivered to the load

iv. PIV across each diode.

v. Ripple voltage and its frequency. [6+10]

4. (a) For a small signal JFET iD = f(VGS, VDS). Obtain expressions for iD and

hence define gm, rd and µ.

(b) From the definition of gm and rd obtain expression for µ.

(c) For an n-channel silicon FET with a = 3×10−4cm and ND = 1015 electrons/cm3.

Find the pinch off voltage. [5+5+6]

5. (a) Prove that stability factor S′′ = (IC1−ICO1)S2

1( 2+1) where S2 is the value of stabilizing

factor S when β = β2

(b) Draw a circuit employing a sensistor compensation and explain its working.

[8+8]

1 of 2

Code No: 07A10401 Set No. 2

6. (a) Draw the equivalent circuit for the CE and CC configurations subject to the

restriction that RL=0. Show that the input impedance of the two circuits are

identical.

(b) For any single-transistor amplifier prove that Ri = hi

1−hrAv

. [8+8]

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+8]

8. (a) Draw the circuit diagram of a transistor phase-shift oscillator and discuss its

operation. Obtain an expression for its frequency of oscillation.

(b) What is the range of frequencies over which a crystal oscillator may be nor-

mally used and why? [8+8]

⋆ ⋆ ⋆ ⋆ ⋆

I B.Tech Regular Examinations, May/Jun 2008

BASIC ELECTRONIC DEVICES AND CIRCUITS

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. (a) An electron is moving perpendicular to magnetic field ‘B’. Derive the expres-sion 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. [8+8]

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 cur-

rent. [8+8]

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.

[8+8]

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 tran-

sistor. [8+8]

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. [7+9]

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 parame-

ters, hie=1K

, hfe=100, hre=5×10−4, hoe= 2×10−5

−1 Rs=15K

, RL=5k

.

Determine input impedance, output impedance, current gain and voltage gain.

[8+8]

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+8]

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’). [8+8]

I B.Tech Regular Examinations, May/Jun 2008

BASIC ELECTRONIC DEVICES AND CIRCUITS

(Electrical & Electronic Engineering)

Time: 3 hours Max Marks: 80

Answer any FIVE Questions

All Questions carry equal marks

⋆ ⋆ ⋆ ⋆ ⋆

1. (a) Draw the schematic diagram of a CRT and explain about the various sectionsand the materials used.

(b) In a CRT, the electrons emitted are accelerated by a potential of 500V. The

length of the deflecting plates is 1.3 cm. Distance between the deflecting plates

is 0.5 cm. The distance between the centre of the deflecting plates and the

screen is 20 cm. Determine the value of electrostatic deflection sensitivity.

[8+8]

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 cur-

rent. [8+8]

3. (a) Discuss the operation of HW recitifier with and without capacitor filter.

(b) Draw the Half wave rectifier circuit using a step down Transformer with Vs

= 46 sin(100π t) and a semiconductor diode. Calculate the turns ratio of

the Transformer windings when the primary voltage of the Transformer is 230

volts. [8+8]

4. (a) Give the UJT symbol and simplified equivalent circuit with external resistors

included.

(b) Draw UJT emitter characteristics and mention various regions.

(c) If VE<VP and VE>VP , explain how UJT works for these conditions.[6+5+5]

5. (a) What is the necessity to stabilize the operating point of transistor amplifier?

(b) What is thermal runaway?

(c) For a fixed bias configuration determine Ic, Rc, Rb and Vce using the following

specifications: Vcc=12V, Vc=6V, β =80, Ib = 40 µA. [4+4+8]

6. (a) For a CB configuration, what is the maximum value of RL for which Ri does

not exceed 50

? Transistor parameters are hib=21.6

, hrb = 2.9×10−4, hfb=-

0.98 and hob=0.49µ A/V.

(b) Sketch the circuit of a CD amplifier. Derive the expression for the voltage

gain at low frequencies and what is the order of magnitude of the output

impedance. [8+8]

7. (a) Draw a feedback amplifier in block-diagram form. Identify each block and

state its funcetion.

1 of 2

Code No: 07A10401 Set No. 4

(b) An amplifier has a voltage gain of -100. The feedback ratio if 0.01. Find the

voltage gain with feedback, the output voltage of the feedback amplifier for

an input voltage of 1mv, feedback factor, and feedback voltage? [8+8]

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

(b) Draw the FET crystal oscillator and derive the equation for frequency of os-

cillations. [8+8]

⋆ ⋆ ⋆ ⋆ ⋆

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