# Electronic Circuits January 2007

Note : 1, Answer any FIVE full questions.

2.Assume missing data suitably.

1 a. With a neat diagram explain the constructional feature of CRT and also explain the focusing scheme used in it.

b.  Derive an equation for diffusion capacitance of P-N junction diode.

c.  Distinguish between ideal and practical diodes. Draw piece-wire linear characteristic and explain.

2 a. Draw the circuit diagram of a Bridge rectifier with capacitor filter and also derive the expression for ripple factor and rectifier efficiency.

b.  Explain the working of a double ended clipper using ideal diodes. Give its transfer characteristics.

c.  Explain the tunneling phenomenon in tunnel diodes. Draw its V-I characteristics

3 a. Discuss the causes for bias instability in a transistor.

b. Derive an equation for the stability factor S for a C.E. self bias circuit.

c.  Discuss different types of bias compensation technique used in the transistor circuits.

4 a. Using approximate h-parameter model for the transistor, obtain expressions for Z„ Zo, Av> Ai for a C.E self bias amplifier with un bypassed Re.

b.  For the circuit shown in the Fig. 4(b) find, Rc, Rb> Re, Vce and Vb Fig. 4(b)

5 a. Write the hybrid-Tt model of BJT and briefly explain the various parameters of the model.

b.  Draw the circuit of a bootstrapped emitter follower and explain how it gives higher input impedance than emitter follower.

c.  The cutoff frequencies of a transistor amplifier are fi – 500 Hz and f2 = 400 kHz. The midband voltage gain is 80. Find the voltage gain at 250 Hz.

6   a. For the emitter follower network of Fig. 6(a), determine : i) re ii) Zj iii) Z0 iv) Av v) Aj  Also derive the equations for Zj, Z0, Av and Ai

b. Explain with relevant sketches how power amplifiers are classified. Derive the expression for the conversion efficiency of a class B push pull amplifier.

7 a. With the circuit diagram explain the working principle of a shunt and series voltage regulator. Also obtain the expression for the regulated output voltage.

b.  What is switching regulator? Explain step-down type of switching regulator with a neat block diagram.

8   Write short notes on the following :

a.  Photo diodes

b.  Ebbers Mol model of PNP transistor

c.  Voltage doublers

d.  Class A power amplifier.