Previous Year Questions- Miscellaneous

Q1: Consider the OP AMP based circuit shown in the figure. Ignore the conduction drops of diodes D₁ and D₂. All the components are ideal and the breakdown voltage of the Zener is 5 V. Which of the following statements is true? (2023)

(a) The maximum and minimum values of the output voltage V₀ are +15 V and -10 V, respectively.
(b) The maximum and minimum values of the output voltage V₀ are +5 V and -15 V, respectively.
(c) The maximum and minimum values of the output voltage V₀ are +10 V and -5 V, respectively.
(d) The maximum and minimum values of the output voltage V₀ are +5 V and -10V, respectively.
Ans: (d)
Sol: During positive hall cycle:
∴ D₁ → ON and D₂ → OFF
Redraw the circuit :
∴ V₀ = -V_i
(V₀)_min = -10V
During negative half cycle :
V⁺ > V^-
Zener diode → ON, D₁ → OFF and D₂ → ON  
Redraw the circuit:
∴ (V₀)_max = 5V

Q2: Two monoshot multivibrators, one positive edge triggered (M₁) and another negative edge triggered (M₂), are connected as shown in figure
The monoshots (M₁) and (M₂) when triggered produce pulses of width (T₁) and (T₂) respectively, where (T₁>T₂) . The steady state output voltage (v_o) of the circuit is (SET-3 (2014))
(a) (b) (c) (d)  Ans: (c)

Q3: The following circuit has a source voltage V_s as shown in the graph. The current through the circuit is also shown. (2009)
The element connected between a and b could be (2009)
(a) (b) (c) (d) Ans: (a)
Sol: Diode act as a switch. When forward biased it is short circuited. But when suddenly reverse biased, current does not become zero instantly , initially the same current flow in opposite direction and after some time (turn off time) it will become zero.

Q4: The truth table of monoshot shown in the figure is given in the table below :
Two monoshots, one positive edge triggered and other negative edge triggered, are connected shown in the figure, The pulse widths of the two monoshot outputs Q₁ and Q₂ are T_ON1 and T_ON2 respectively.
The frequency and the duty cycle of the signal at Q₁ will respectively be (2008)
(a)

(b)
(c)
(d)
Ans: (a)
Sol:

Q5: IC 555 in the adjacent figure is configured as an astable multi-vibrator. It is enabled to to oscillate at t = 0 by applying a high input to pin 4.
The pin description is :
1 and 8-supply;
2-trigger;
4-reset;
6-threshold
7-discharge.
The waveform appearing across the capacitor starting from t = 0, as observed on a storage CRO is (2007)
 (a) (b) (c)
(d) Ans:

Q6: The input signal v_in shown in the figure is a 1 kHz square wave voltage that alternates between +7 V and -7 V with a 50% duty cycle. Both transistor have the same current gain which is large. The circuit delivers power to the load resistor R_L. What is the efficiency of this circuit for the given input ? choose the closest answer. (2007)(a) 46%
(b) 55%
(c) 63%
(d) 92%
Ans:

Q7: In the Schmitt trigger circuit shown in figure, if V_CE(sat) = 0.1V, the output logic low level (V_OL) is (2004)
(a) 1.25 V
(b) 1.35 V
(c) 2.50 V
(d) 5.00 V
Ans:

Q8: The circuit of figure shows a 555 Timer IC connected as an astable multivibrator. The value of the capacitor C is 10 nF. The values of the resistors R_A and R_B for a frequency of 10 kHz and a duty cycle of 0.75 for the output voltage waveform are (2003)
(a) R_A = 3.62kΩ, R_B = 3.62kΩ
(b) $RA=3.62k\Omega ,RB=7.25k\Omega$R_A = 3.62kΩ, R_B = 7.25kΩ
(c) R_A = 7.25kΩ, R_B = 3.62kΩ
(d) $RA=7.25k\Omega ,RB=7.25k\Omega$R_A = 7.25kΩ, R_B = 7.25kΩ
Ans: