Analog Electronics — DU B.Sc. (Hons) Physics Previous Year Question Papers

Medium of setting the Question paper: English Language (a) Sketch typical output characteristics curves for a PNP transistor in CB configuration. Label all variables and indicate the active, cut-off and saturation regions of operation. (b) What value of a series resistance is required to limit the current through a LED to 20 mA with a forward voltage drop of 1.6V when connected to a 10 V supply. (c) What is Barkhausen criterion for sustained oscillations? (d) Write equations for h-parameter model of an NPN transistor in CE configuration, and draw its equivalent circuit. (e) An Op-Amp has a CMRR value of 55 dB and a differential mode gain of 1200. Find the common mode gain. (f) Draw the circuit for the zero-crossing detector using an Op-Amp. Draw the output waveform if the input is a 1kHz sinusoidal waveform and peak value 50 mV. Q-2 (a) Derive the expressions for the r.m.s value of current, ripple factor and rectification efficiency of a Full wave bridge rectifier. Also sketch the output waveform resulting from a sinusoidal input voltage. What is the P.I.V of each diode used in the circuit. (10) (b) A transistor is connected in common emitter (CE) configuration in which Vcc is 8V and voltage drop across collector resistance (Rc) is 0.5V and Rc= 800 Ω. If alpha=0.96 determine (i) Collector- emitter voltage (ii) base current (IB) (5) Q-3 (a) Over what range of input voltage will the Zener circuit shown below will maintain 30 V across RL=2000Ω, assuming that series resistance R=200Ω and Zener current rating is 25 (b) For the circuit given below, find (i) IB (ii) IC (iii) IE and (iv) VCE. Neglect VBE. (c) Draw the output waveform corresponding to a sinusoidal input signal of frequency 1 kHz and amplitude 50mV applied to the inverting input of an ideal op-amp. The op-amp is operating in open loop configuration with supply voltages ± 15V. (5) Q-4 (a) Draw the circuit diagram of a 3 section RC Phase Shift Oscillator, and derive the expression for frequency of the generated oscillations. (10) (b) Determine the oscillating frequency of a BJT Hartley oscillator, given the component values as L1=L2=4.7mH, C1=600 pF and the mutual inductance between (5) Q-5 (a) Explain the working of an ideal integrator circuit designed using Op-amp. Explain the problems associated with the ideal circuit and how they are rectified in a practical integrator. Draw the frequency response of the ideal and practical Integrator and mark the region of integration for the practical integration. (10) (b) In a non-inverting summing amplifier, input voltages Vi = 2 V and V2 = 4V are applied through resistors 10kS and 20kS respectively. If Rf = 30kS and Ri = 10kS, calculate the output voltage. (5)