Anna University - Electronic Devices and Circuits Question paper - APRIL/MAY 2010

Third SemesterElectrical and Electronics Engineering

(Regulation 2008)

Time: Three hours Maximum: 100 Marks
Answer ALL Questions

PART A — (10 × 2 = 20 Marks)

1. What is meant by diffusion current in a semi conductor?
2. A silicon diode has a saturation current of 7.5µ A at room temperature 300°K.
Calculate the saturation current at 400°K.
3. Draw the input and output characteristics of a transistor in CE configuration
and mark the cutoff, saturation and active regions.
4. State the advantages of optocoupler. (Write any four).
5. Compare JFET with BJT.
6. Define amplification factor in JFET.
7. Define CMRR and write its significance in differential amplifiers.
8. List the advantages of negative feedback amplifiers.
9. Sketch the idealized characteristics for the filter types.
(a) Low pass
(b) High pass
(c) Band pass
(d) Band reject filters.
10. Define intrinsic stand off ratio of UJT and draw its equivalent circuit.

PART B — (5 × 16 = 80 Marks)

11. (a) With a neat diagram explain the working of a PN junction diode in
forward bias and reverse bias and show the effect of temperature on its
V-I characteristics. (Marks 16)
(b) (i) Explain V-I characteristics of Zener diode. (Marks 8)
(ii) Draw the circuit diagram and explain the working of full wave
bridge rectifier and derive the expression for average output
current and rectification efficiency. (Marks 8)

12. (a) (i) Draw the h-parameter equivalent circuit of a transistor in CE
configuration. (Marks 8)
(ii) Describe the methods of determination of h-parameters from its
static Input and output characteristics. (Marks 8)
(b) (i) Explain the important characteristics of optocoupler. (Marks 6)
(ii) Explain the switching characteristics of transistor with neat sketch.
(Marks 10)

13. (a) (i) Explain how the transconductance of a JFET varies with drain
current and gate voltage characteristics and transfer
characteristics. (Marks 12)
(ii) A JFET has the following parameters IDDS = 32 mA,
VGS(off) = -8 Volts, VGS = -4.5 Volts. Find the values of drain
current. (Marks 4)
(b) (i) Explain the working of n-channel enhancement type MOSFET.
Sketch its typical characteristics. (Marks 10)
(ii) Explain the application of FET as a voltage variable resistor. (Marks 6)

14. (a) (i) Draw the block diagram of a voltage series feedback amplifier and
derive the equation for input impedance, output impedance and the
voltage gain. (Marks 10)
(ii) Calculate the voltage gain, input and output resistances of a voltage
series feedback amplifier having AV = 300, Ri = 1.5 k, Ro = 50 k
and ß = 1/15. (Marks 6)
(b) (i) Differentiate oscillator with amplifier. (Marks 4)
(ii) Draw the circuit of a Hartley oscillator and derive the condition for
the frequency of oscillation. (Marks 12)

15. (a) (i) Describe the operation of UJT and its emitter characteristics. (Marks 8)
(ii) Describe the working of a Schmitt trigger circuit with the help of
necessary waveforms. (Marks 8)
(b) (i) Sketch the response of RC high pass filter for the following inputs
and explain.
(1) Ramp
(2) Pulse. (Marks 8)
(ii) Explain the operation of a bistable multi-vibrator circuit with neat
sketch. (Marks 8)

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