RR
Code No: RR100207
I B.Tech (RR) Supplementary Examinations, June 2009 ELECTRONIC DEVICES AND CIRCUITS (Common to Electrical & Electronics Engineering, Electronics & Communication Engineering, Computer Science & Engineering, Electronics & Instrumentation Engineering, Bio-Medical Engineering, Information Technology, Electronics & Control Engineering, Computer Science & Systems Engineering, Electronics & Computer Engineering and Instrumentation & Control Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Give the block diagram of CRO and explain about each block in detail? (b) In a electrostatic deflecting CRT the length of the deflection plats is 2cm, and spacing between deflecting is 0.5cm, The distance from the cenlve of the deflecting plate to the screen is 20cm, the deflecting voltage is 25V Find the deflecting sensitivity, the angle of diction and velocity of the beam. Assume final anode potential is 1000V [8+8] 2. (a) Explain about various current components in a forward biased p-n junction diode. (b) Find the value of D.C. resistance and A.C resistance of a Germanium junction diode at 250 C with Io = 25µA and at an applied voltage of 0.2V across the diode. [8+8] 3. (a) Explain the circuit diagram of a single phase full-wave bridge rectifier and sketch the input, output waveforms. (b) Define percentage regulation and prove that the regulation of both half wave and full wave rectifier R is given by percentage regulation is equal to RLf × 100% [8+8] 4. (a) A Germanium transistor with α = 0.98 gives a reverse saturation current ICO = 12mA when used in CB configuration. Calculate the collector current in CE mode for a base current of 0.2mA. (b) Sketch the profiles of majority and minority carrier currents in the base of an NPN transistor. Explain the transistor action with the help of these profiles. [6+10] 5. (a) Draw the structure of photo transistor and give its working principle? (b) What are the advantages of phototransistor over photo diode? (c) Draw the characteristics of phototransistor.
[8+4+4]
6. (a) Draw the circuit diagram of a collector to base bias circuit of CE amplifier and derive expression for S. (b) Determine the quiescent currents and the collector to emitter voltage for a germanium transistor with β=50 in self biasing arrangement. Draw the circuit with a given component value VCC = 20V, RC = 2K, Re = 100Ω R1 = 100KΩ R2 = 5K. Also find out stability factor. [8+8] 7. (a) Classify the amplifiers based as feedback topology and give their block diagram. How the input and output impendence are effected in each case. (b) Draw the circuit diagram of a current feed back circuit and derive Expressions for Voltage gain and output resistance, and input resistance. [8+8] 8. (a) Show that the gain of Wien bridge oscillator using BJT amplifier must be at least 3 for the oscillations to occur. (b) In a transistorized Hartley oscillator the two inductances are 2mH and 20µH while the frequency is to be changed from 950KHZ to 2050KHZ. Calculate the range over which the capacitor is to be vaired. [10+6] ?????