Edc Q1

ELECTRONIC DEVICES AND CIRCUITS Time : Three hours Maximum : 100 marks Answer ALL questions. PART A — (10 ? 2 = 20 marks) 1. Define a hole. What is its importance? 2. The current flowing in a PN junction diode at room temperature is A, when a large reverse bias voltage is applied. Calculate the current flowing, when 0.1 V forward bias is applied at room temperature. 3. List the three sources of instability of collector current. 4. Define in words and also as a partial derivative (a) (b) (c) (d) 5. What are the four possible topologies of a negative feedback amplifier? 6. Give the two Barkhausen conditions required for the sinusoidal oscillations to be sustained. 7. Draw the schematic block diagram of the basic op–amp with inverting and non inverting inputs and also draw the equivalent circuit. 8. Define : (a) Power supply rejection ratio (b) Slew rate for an op–amp. 9. Sketch the idealized characteristics for the filter types (a) Low pass (b) High pass (c) Band pass (d) Band reject filters. 10. List any four uses of Multivibrators. PART B — (5 ? 16 = 80 marks) 11. (i) Draw the circuit diagram and output characteristics of a NPN transistor in CB configuration. Indicate the active, cutoff and saturation regions and explain the significance of the curve qualitatively. (10) (ii) In the circuit shown below, VCC = 24 V, RC = 10 k , RE = 270 . If a silicon transistor is used with = 45 and if VCE = 5 V, find R. Neglect the reverse saturation current. (6) 12. (a) (i) In an open circuit PN junction, plot the space charge, electric field, electrostatic potential variation as a function of distance across the junction. (8) (ii) Write the Volt–Ampere diode equation for a PN diode. With the help of this equation, explain the Volt–Ampere characteristics of a diode. (8) Or (b) (i) What are the requirements of a biasing circuit. (4) (ii) Define stabilization technique and compensation technique. (4) (iii) A CE amplifier with self bias arrangement as shown in figure employ an NPN transistor having = 99, and stability factor S of 5. Calculate the values of R1, R2 and RE if the values of resistance RC and various voltages are as shown in figure. (8) 13. (a) (i) Draw the small signal equivalent circuit for CE transistor amplifier and deduce the expressions for current gain, input impedance, output impedance and voltage gain. (10) (ii) A transistor used in a common base amplifier has the values of

h–Parameters Calculate the values of current gain, input resistance and voltage gain. Assume source resistance is zero. (6) Or (b) (i) Draw the block diagram of an amplifier with a feedback network and derive the expression for the voltage gain. (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 = 1/15. (6) 14. (a) (i) Differentiate oscillator with amplifier. (4) (ii) Briefly explain how oscillators are classified. (4) (iii) Draw the circuit diagram and explain the principle of operation Hartley oscillator. (8) Or (b) (i) List out the characteristics of ideal op–amp. (4) (ii) Draw the circuit diagram of op–amp used in inverting amplifier and obtain the formula for voltage gain and VO. (4) (iii) In fig. R1 = 10 k , Rf = 100 k , Vi = 1 V. A load of 25 k is connected to the output terminal. Calculate (1) I1 (2) V0 (3) IL and total current I0 in to the output pin. (8) 15. (a) (i) Draw the circuit of a Differentiator using op–amp and obtain the formula for output voltage and magnitude gain. (8) (ii) Draw the circuit diagram with equation for V0 of an instrumentation amplifier and write down its important features and application. (8) Or (b) (i) Sketch the collector coupled astable multivibrator circuit. (4) (ii) Determine period and frequency of oscillations for an astable multivibrator with components values R1 = 2 k , R2 = 20 k , C1 = 0.01 f, C2 = 0.05 f. (4) (iii) Draw and explain the functional diagram of a 555 Timer. (8)