solution for electronics devices and circuits · (b) draw the hybrid equivalent model of voltage...

Mumbai University Electrical (Semester -III)

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Solution for Electronics Devices

and Circuits

May 2016

Index

Q.1)

a) …………………………………………………………………………. 2-3

b) …………………………………………………………………………. 4

c) …………………………………………………………………………. 5

d) …………………………………………………………………………. 5-6

Q.2)

a) …………………………………………………………………………. 7

b) …………………………………………………………………………. 8-10

Q.3)

a) …………………………………………………………………………. 11-17

b) …………………………………………………………………………. N.A

Q.4)

a) …………………………………………………………………………. N.A

b) …………………………………………………………………………. 18-19

Q.5)

a) …………………………………………………………………………. 20-24

b) …………………………………………………………………………. N.A

Q.6)

a) …………………………………………………………………………. 25-28

b) …………………………………………………………………………. 29-31



Q.1)

A) Draw the block diagram of a DC power supply and explain the terms.

a) rectification efficiency b) Ripple factor (RF) c) PIV (05)

Ans :- Block Diagram of DC Power Supply

a)



c)

..



B) State the advantage of negative feedback. (05)

Ans:- Negative Feedback

Advantage of Negative Feedback :-

Disadvantage of Negative Feedback :-

Application of Negative Feedback :-



C) Compare RC and LC oscillators. (05)

Ans:-

Sr. no. RC oscillators LC oscillators

D) Explain with V-I characteristics the working principle of a schottky diode.

(05)

Ans:-V-I Characteristic :-



Q.2)

(A) Explain the Barkhausen Criteria of Oscillators. (10)

Ans :- Barkhausen Criteria

The Barkhausen criteria should be satisfied by an amplifier with the positive feedback to ensure the sustained oscillations.

For an oscillator circuit ,there is no input signal “Vs” , hence the feedback signal Vf itself should be sufficient to maintain the oscillations.

The



(B) Draw the hybrid equivalent model of voltage divider has CE amplifier

with RE bypassed and derive the expression for voltage gain and input

impedance.

(10)

Ans :- Simplified CE Hybrid Amplifier

Therefore we can neglect hre and hoc while drawing the h-parameter

equivalent circuit is called as the approximate hybrid equivalent circuit.

Note that the dependent voltage source hre and Vce has been replaced by

a short circuit and hce has been replaced by an open circuit.

Analysis of CE Amplifier with Bypassed RE :-

The figure (a) below shows the CE amplifier with bypassed RE and

Figure (b) shows its ac equivalent circuit



Q.3)

A) Draw the small signal equivalent of n-channel JFET amplifier with Rs

bypassed and un bypassed derive the expression for voltage gain in each

case. (10)

Ans :- JFET Amplifier

Analysis:

Let us obtain the expression for Z1 Z0 and Av for the self bias

configuration .

Compare the small signal equivalent circuit drawn in figure with the

small signal equivalent circuit of the fixed bias configuration.



Ex. Of n-channel JFET :-



CS JFET Amplifier with self Bias (Unbypassed Rs )



B) Find the voltage gain of a two stage caseadad JFET amplifier with the

following parameters.

VDD = 20V , RG1 = RG2 = 3.3 Ω , RD1 = RD2 = 2.4 Ω , RS1 = RS2 = 680 Ω IDSS = 10

mA , Vp = -4V (10)

Ans :- N. A.

Q.4)

A) Explain the different thermal compensation techniques in BJT amplifier. (10)

Ans :- N. A.



B) State and draw each topology of negative feedback and explain the effect

on i/p impedance, o/p impedance and voltage gain for Current Series Negative

Feedback. (10)

Ans :- Negative feedback

Voltage series feedback :-



Voltage shunt feedback :-

Current Shunt feedback :-



Q.5)

A) Draw the circuit diagram of dual input balanced output (DIBO) differential

amplifier and derive the relevant AC parameters. (10)

Ans :-

AC Analysis :-

The next step in ac analysis is to draw the approximate h-parameter

model of the equivalent circuit shown in figure



The expression for their voltage gain Ad , input resistance Rin and output

resistance R0 are as listed in table.

B) Derive the equation for frequency of oscillation of RC phase shift oscillators

using JFET as basic amplifier Derive the condition of Oscillation. (10)

Ans :- N.A

v



Q.6) Draw neat diagram of UJT relaxation oscillator. Explain its operation.

Derive the expression for frequency of output signal. Draw various waveforms.

(10)

Ans :- UJT Reflection Oscillator



The capacitor charges through the potentiometer R. When the capacitor

voltage equals the peak voltage Vp of the UJT ,it turns on.

Then the capacitor discharges through emitter (E) ,base (B1) and primary

winding of the pulse transformer .

Due to primary current, a pulse is generated on the secondary side of

the pulse transformer.

The capacitor voltage and secondary pulses are as shown in the figures

respectively.

These pulses are used as triggering pulses for the SCR.

As the capacitor discharges and Vc reaches the point voltage VV ,the UJT

is turned off and the capacitor starts charging again through R.

The charging rate of the capacitor is decided by the value R .Therefore it

is possible to change the firing angle α by varying the potentiometer

R.the firing angle can be changed from 0 to 180 0.

c



B) What is Darlington configuration? Derive the expression of voltage gain of

Darlington pair emitter follower. (10)

Ans :- Darlington Pair

1) Emitter Follower using Darlington pair :-



2) Analysis of Darlington Emitter Follower :-

Voltage gains of Darlington Connection :-

The overall voltage gain Av is given by,

So let us obtain the expression for the individual voltage gains Av1 and

Av2.

Voltage gain for second stage Is obtained by using approximate

analysis and Av1 is obtained by using the exact analysis.

solution for electronics devices and circuits · (b) draw the hybrid equivalent model of voltage...

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