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Code No: Y0221/R07 Set No. 1

I B.Tech Regular Examinations, May 2010BASIC ELECTRONIC DEVICES AND CIRCUITS

(Electrical & Electronic Engineering)Time: 3 hours Max Marks: 80

Answer any FIVE QuestionsAll Questions carry equal marks

1. (a) List out the advantages and disadvantages of both electrostatic and electromagnetic deflection system?

(b) Explain the following terms:

i. Potential

ii. Electron Voltiii. Charge density

iv. Current density. [8+8]

2. (a) Determine the resistivity of Germanium:

i. in intrinsic condition at 300 0K

ii. with donor impurity of 1 in 107

iii. with acceptor impurity of 1 in 108

Given for germanium at room temperature. ni = 2.5 1013/cm3; p

= 1800 cm2/V-sec, n = 3800 cm2/V-sec and number of Germanium

atoms/cm3 = 4.4 1022.

(b) Compare Avalanche and Zener breakdown. [10+6]

3. (a) Explain the circuit diagram of a single phase full-wave bridge rectifier andsketch the input and output wave forms.

(b) Define percentage regulation and prove that the regulation of both half waveand full wave rectifier is given by percentage regulation equal to Rf

Rl 100%.

[8+8]

4. (a) Compare BJT, JFET and MOSFET in all respects.

(b) Draw the static characteristics of SCR for different gate currents and explainbriefly. [8+8]

5. What is meant by compensation? Explain the different types of compensationtechniques with neat circuit diagrams and also compare this with stabilizationtechniques. [16]

6. Obtain CC h parameters in terms of CE h parameters. [16]

7. (a) Define Desensitivity D. What is the significance of this?

1 of 2ase purchase PDF Split-Merge on www.verypdf.com to remove this watermark.

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(b) An amplifier without feedback gives a fundamental output of 36V with 7percent second-harmonic distortion when the input is 0.028V. If 1.2 percentof the output is fed back into the input in a negative voltage series feedbackcircuit, what is the output voltage? If the fundamental output is maintainedat 36V but the second-harmonic distortion is reduced to 1 percent, what isthe input voltage? [6+10]

8. (a) Give the two Barkhausen conditions required in order for sinusoidal oscillationsto be sustained.

(b) Calculate the series resonant frequency and the parallel resonant frequencyof a crystal oscillator, if the values are L=20H, C=0.05pF, R = 2K andCM=10PF. [8+8]


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1. (a) With the help of a block schematic, explain the working of a CRO and whatare the applications of CRO?

(b) In a CRT, a pair of deflecting plates are 2.5 cm long and 0.5 cm apart. Thedistance from the centre of the plates to the screen is 20 cm. The final anodevoltage is 1200V. Calculate:

i. The displacement produced for a deflecting voltage of 20V

ii. The angle, which the beam makes with the axis of the tube on emergingfrom the field. [10+6]

2. (a) With a neat schematic diagram explain the working of Tunnel diode and alsodiscuss about its V-I characteristics.

(b) The current through silicon diode, If=60 mA for a forward bias of Vf = 0.6Volts. Calculate the static resistance. [10+6]

3. (a) A 15-0-15 Volts (rms) ideal transformer is used with a full wave rectifier circuitwith diodes having forward drop of 1 volt. The load is a resistance of 100ohm

and a capacitor of 10,000f is used as a filter across the load resistance. Cal-culate the dc load current and voltage.

(b) Draw the circuit diagram of a bridge rectifier circuit with L-section filter andexplain its operation. [8+8]

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

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

(c) For an n-channel silicon FET with a = 3104cm and ND = 1015 electrons/cm3.

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

5. (a) What do you understand by dc and ac load line? Explain how to choose theoperating point?

(b) For a fixed bias configuration, determine IbQ, ICQ and VceQ using the followingspecifications: Vcc= 16V, =90, Rc = 2.7K, Rb=470K and also find thesaturation current Isat. [8+8]

6. (a) Explain the method of evaluating h parameters for a transistor in CB config-uration.


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(b) A CC amplifier is driven by a voltage source of internal resistance R s=1k.The load impedance if RL=1K. The transistor parameters are hic= 1.1K,hfc = -51, hrc=1, hoc= 25A/V. Compute input and output impedance of theamplifier. [8+8]

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

(b) Find Af for a CE stage with an un bypassed emitter resistor. [8+8]

8. Verify the following equations for the transistor phase-shift oscillator of shown infigure 8.f = 1

2RC16+4k

hfe = 4k + 23 + 29/kWhere k=Rc/R [16]

Figure 8


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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 theCRT. [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 andreverse bias and explain. [6+10]

3. (a) Draw the circuit diagram of a Half wave rectifier. Explain the operation ofthe circuit with relevant waveforms.

(b) A bridge rectifier uses four identical diodes having forward resistance of 5each. Transformer secondary resistance is 5 ohms and the secondary voltageis 30 V (rms). Determine the dc output voltage for Idc = 200 mA and valueof the output ripple voltage. [8+8]

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

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

(c) If VEVP, explain how UJT works for these conditions.[6+5+5]

5. (a) Show that stability factor may be put in the formS= Ge+G1+G2Ge/(1+)+G1+G2Where the Gs are the conductances.

(b) What is heat sink? Why it is used?

(c) What is the condition for avoiding thermal runaway problem? [8+4+4]

6. Show that the exact expression for hfb in terms of the CB hybrid parameters is

hfb = hfe (1hre)+hiehoe

(1+hfe )(1hre)+hoehie

from this formula obtain the approximate expression for hfe . [116]

7. (a) List the procedures to follow to obtain the basic amplifier configuration with-out feedback but taking the loading of the feedback network into account.

(b) Prove that for voltage-series feedback with Rs = 0, AIf = AI. [8+8]


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8. (a) Prove that a transistor with a small signal common emitter short circuit cur-rent gain less than 44.5 cannot be used in the phase shift oscillator and alsodraw the corresponding circuit.

(b) Draw the crystal oscillator circuit and explain how it generate oscillations.[6+10]


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1. (a) With the help of a block schematic, explain the working of a CRO and whatare the applications of CRO?

(b) In a CRT, a pair of deflecting plates are 2.5 cm long and 0.5 cm apart. Thedistance from the centre of the plates to the screen is 20 cm. The final anodevoltage is 1200V. Calculate:

i. The displacement produced for a deflecting voltage of 20V

ii. The angle, which the beam makes with the axis of the tube on emergingfrom the field. [10+6]

2. (a) Draw and explain the V-I characteristics of a p-n junction diode. Use equationswherever necessary.

(b) The transition capacitance of an abrupt junction diode is 30pf at 8V. Deter-mine the value of capacitance for an increase in the bias voltage of 2V.

[8+8]

3. (a) Derive the expression for DC value of current, R.M.S value of current and

Average voltage across the load for a half wave rectifier.

(b) Compare the performance of series inductor, L-section and -section filters.[8+8]

4. (a) Compare BJT, JFET and MOSFET in all respects.

(b) Draw the static characteristics of SCR for different gate currents and explainbriefly. [8+8]

5. (a) Determine the stability factor for the circuit shown in figure 5a.


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Figure 5a

(b) Calculate the thermal resistance for the 2N338 transistor for which the manu-facturer specifies Pc,max=125mW at 25

0C free-air temperature and maximumjunction temperature Tj=150

0C. What is the junction temperature if the col-lector dissipation is 75mW? [8+8]

6. (a) Explain the method of evaluating h parameters for a transistor in CB config-uration.

(b) A CC amplifier is driven by a voltage source of internal resistance R s=1k.The load impedance if RL=1K. The transistor parameters are hic= 1.1K,

hfc = -51, hrc=1, hoc= 25A/V. Compute input and output impedance of theamplifier. [8+8]

7. (a) Define Desensitivity D. What is the significance of this?

(b) An amplifier without feedback gives a fundamental output of 36V with 7percent second-harmonic distortion when the input is 0.028V. If 1.2 percentof the output is fed back into the input in a negative voltage series feedbackcircuit, what is the output voltage? If the fundamental output is maintainedat 36V but the second-harmonic distortion is reduced to 1 percent, what isthe input voltage? [6+10]

8. (a) Sketch the circuit of a phase shift oscillator using a bipolar junction transistor

and explain its operation.

(b) Draw the circuit diagram of a crystal oscillator. What are the advantages ofa crystal oscillator over an other oscillators? [8+8]


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