IGNOU PHE-10 - Electrical Circuits and Electronics

1. State, with reasons, whether the following statements are True or False: i) Thevenin’s theorem is valid only for resistive networks. ii) Impedance matching is the necessary condition for proper operation of any electronic system. iii) In practical rectifier circuit, the peak amplitude of the output voltage is always smaller than the input peak amplitude. iv) The mid band gain of an amplifier is 50 dB, then its gain at cut-off frequencies equals 25 dB. v) By using positive feedback, the gain of an amplifier can be stabilized. vi) CMRR of an op-amp determines its highest operating frequency. vii) 79XX series voltage regulator IC cannot provide output current more than 10 mA. viii)Only the decimal numbers divisible by 8 can be represented by octal system. ix) Truth table of a 3-input OR gate is same as that of a 3-input NAND gate. x) X and Y inputs of CRO can be used to directly measure the current flowing through a given circuit. 2. Using superposition principle obtain the voltage across the load resistance RL and the current flowing through it in the circuit given in Fig. 1. 3. a) Explain the statement “Bipolar Junction Transistor is a current controlled device while Field Effect Transistor is a voltage controlled device”. b) Calculate the resonance frequency, bandwidth and Q-factor of the circuit shown in Fig. 2. 4. a) In the universal biasing of a transistor, which resistor acts as a feedback element? How does it provide stability to the circuit? b) Why is a class B amplifier more efficient than class A amplifier? What will be the effect on the output of a push-pull amplifier if unmatched transistors are used? 5. a) Why are LC oscillators preferred over RC oscillators to generate high frequencies? Why is a 2-stage amplifier required in Wein bridge oscillator in contrast to a single stage amplifier in the phase shift oscillator? b) Design and draw a zener voltage regulator to provide 5V output if load resistance varies between 100 Ω and 500 Ω. Assume that the input unregulated dc voltage is 6V and minimum zener operating current is 5 mA. 6. a) Compare the characteristics of IC 741C with an ideal op amp. b) Design an op amp comparator to provide +VSAT output for input signal less than +1V and -VSAT output for input signal more than +1V. 7. a) Draw the output waveform indicating proper scales on the time and voltage axes for the given input waveform to the circuit shown in Fig. 3. b) Design and draw voltage regulator to provide 2 to 10V variable output voltage using IC 7812. 8. a) Convert 0001010001001001 (BCD) into its binary equivalent and then divide it by 10012. Express the result in octal equivalent. b) Find the MSP expression for following relation and draw its logic gate implementation with minimum number of gates. 9. a) Explain the working of synchronous counter. b) Discuss the working of signal generator circuit.