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

(b) An operational amplifier is used as a comparator in the following configuration: Vin(t) = 4sin(1000rt) V, Vor = 2 V, Voo==10 V. Calculate the output voltage of the Op-Amp. Draw the output voltage waveform of the Op-Amp, when the input signal crosses Vres = 2V. (7) 5. (a) Design an astable multivibrator circuit using a 555 timer to generate a rectangular wave of frequency 1 kHz with a duty cycle of 60%. Calculate the values of resistors R, and R,. Assume C = 0.1 MF for calculations. If the timing capacitor C is doubled, calculate the time period of the output waveform? (8) (b) Compare the behaviour of RC integrator and differentiator in terms of their frequency response. Describe scenarios where you would use a low-pass filter versus a high-pass filter. (7) Answer any five of the following questions. (a) Define the term "cut-off frequency" in an RC circuit with proper diagram. (b) Describe the working principle of a light-emitting diode (LED) with the help of an appropriate diagram. (c) The ac input to a diode clamper is a sinusoidal waveform of Vpp , = 8V and f = 1KHz. Draw circuit diagram of a diode Clamper circuit that inserts a positive de level (+1V) in the output wave-form. Also draw the waveform. (d) A transistor operating in the common-emitter configuration has I, = 4.5 mA, and I, = 0.1 mA. Calculate the common-emitter current gain (B) and common-base current gain (a). (e) Convert the decimal number 5.75lo into binary and octal equivalent. (f) A differential amplifier has a CMRR of 80 dB, a differential gain (A) of 10,000 and a common-mode input signal (Vem) of 1 V. Calculate the output voltage contributed by the common-mode signal. 2. (a) Derive the expressions for the DC output voltage (Vac). and peak inverse voltage (PIV) of a full-wave bridge rectifier with the help of a suitable diagram. Draw the output waveform when a C-filter is used in the above circuit. (8) (b) A Zener diode has a breakdown voltage of 6V. It is connected in reverse bias configuration across a load resistance Ry = 1kS. The series resistance Rs = 3300. The input voltage varies between 8 V and 12 V. Calculate the Zener current at V, = 8 V and V, = 12V. Also calculate the power dissipated in the Zener diode when V, = 12V. 3. (a) Explain the working of a Bipolar Junction Transistor (BJT) circuit as a switch. Draw the input-output characteristics of a BJT acting as a switch. Label the cut-off and saturation regions on the graph. (8) (b) Derive the Boolean expressions for the Difference and Borrow outputs of a Full Subtractor logic circuit. Implement the circuit using minimum number of 2-input NAND gates. (7) 4. (a) An operational amplifier is connected in a subtractor configuration with V, = 15 V, V2 = 5 V, R, = 20 kR, R, = 10kS and R, = 40 kR. Calculate the output voltage. If the resistor R, is increased to 40 kS, how will the output voltage change? Explain the effect of resistor values on the output voltage. (8)