ELECTRONIC DEVICES & CIRCUITS PAPER 1

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ELECTRONIC DEVICES AND CIRCUITS (New) EC 201 3rd Sem May 2k5

Note: Section A is compulsory. Attempt any Four questions from Section B and two from Section C

Section A Marks 2 each

1.

• compare the characteristics of silicon and a germanium diode and determine which you would prefer to use for most practical applications.
• What will happen to output a.c. signal if the d.c. level is insufficient in an amplifier? Sketch the effect on waveform.
• What do you mean by Gain_Bandwidth product?
• Explain the concept of photoconductivity.
• What is programmable UJT?
• What is thermal runaway?
• What do you mean by Rise Time, Fall Time and Propagation Delay?
• What is ripple factor?
• Which of three configurations of BJT has a low voltage gain and highest output resistance? Why?
• What is Shockley equation?

Section B Marks 5 each

2. (a) Describe why IG is effectively zero amperes for a JFET transistor.
(b) Why is input impedance to a JFET so high?
(c) Why is terminology field effect appropriate for this three-terminal device?

3. Explain Bias compensation Methods.

4. Given IE = 2.5 mA, the=140, hoe=20ms (m mho) and hdb=o.5 ms. Determine:
(a) Common-emitter hybrid equivalent circuit
(b) Common- base remodel.

5. An emitter follower using p-n-p transistor with bo= 150 is at Ic=0.25 mA. The voltage signal source has Rs=3kΩ :
(a) In order to make overall Ro=110 Ω determine RE.
(b) For this value of RE obtain Av and input resistance.

6. Discuss the relative differences in mode of operation between LED and LCD display.

Section C Marks 10 each

7. By drawing neat diagram, explain the working of BJT and FET and state their relative merits.

8. (a) Potential divider biasing from Vcc=15 volts is obtained for an n-p-n transistor. Given R1 72 kΩ, R2=18 kΩ, RE=1.4 kΩ, Rc=4 kΩ. Determine the operating point:
(i) When b=125
(ii) When b is doubled.
Use VBE’= 0.7 V and comment on stability of operating point with change in b.

(b) What is bias stabilization? Determine the general stability factors for all the configurations.

9 (a) In a CE transistor amplifier when signal changes by 0.02 V, the base current changes by 10 mA and collector current by 1 ma. If the collector resistance Rc= 5kΩ and RL=10 kΩ, find:
(i) Voltage gain
(ii) Current gain
(iii) Input impedance
(iv) A.C. load resistance, and
(v) Power gain.
(b) What is Ebers-Moll Model? Explain in detail.