# Multivibrators and 555 Timer

 Question 1
In the astable multivibrator circuit shown in the figure, the frequency of oscillation (in kHz) at the output pin 3 is __________
 A 2.5 B 6.55 C 5.68 D 1.55
GATE EC 2016-SET-3   Analog Circuits
Question 1 Explanation:
$\begin{array}{c} f=\frac{1}{0.69\left(R_{A}+2 R_{B}\right) C} \\ =\frac{1}{0.69\left(2.2 \times 10^{3}+2 \times 4.7 \times 10^{3}\right) \times 0.022 \times 10^{-6}} \\ =5.6818 \mathrm{kHz} \end{array}$
 Question 2
In the following a stable multivibrator circuit, which properties of $v_{0}(t)$ depend on $R_2$?
 A Only the frequency B Only the amplitude C Both the amplitude and the frequency D Neither the amplitude nor the frequency
GATE EC 2009   Analog Circuits
 Question 3
Consider the Schmidt trigger circuit shown below. A triangular wave which goes from -12 to 12 V is applied to the inverting input of OPMAP. Assume that the output of the OPAMP swings from +15 V to -15 V. The voltage at the non-inverting input switches between
 A -12V to +12 V B -7.5 V to 7.5 V C -5 V to +5 V D 0 V and 5 V
GATE EC 2008   Analog Circuits
Question 3 Explanation:
\begin{aligned} \frac{15-V_{1}}{10}+\frac{V_{0}-V_{1}}{10}&=\frac{V_{1}-(-15)}{10} \\ 15-V_{1}+V_{0}-V_{1}&=V_{1}+15 \\ \Rightarrow \quad V_{1}&=\frac{V_{0}}{3} \end{aligned}
since, $V_{0}$ swings from $-15 \vee$ to +15 V,
Therefore, $V_{1}$ switches between $-5 \vee \text{ and } +5 \mathrm{V}$
 Question 4
An astable multivibrator circuit using IC 555 timer is shown below. Assume that the circuit is oscillating steadily.

The voltage $V_c$ across the capacitor varies between
 A 3 V to 5 V B 3 V to 6 V C 3.6 V to 6 V D 3.6 V to 5 V
GATE EC 2008   Analog Circuits
Question 4 Explanation:
$V_{C}$ varies between 3V to 5V.
 Question 5
Given the ideal operational amplifier circuit shown in the figure indicate the correct transfer characteristics assuming ideal diodes with zero cut-in voltage.

 A A B B C C D D
GATE EC 2005   Analog Circuits
Question 5 Explanation:
$V_{u t}=\beta_{u} V_{\text {sat }}$
When lower diode is ON
\begin{aligned} \beta_{u}&=\frac{2 k \Omega}{2.5 \mathrm{k} \Omega} \\ \therefore \quad V_{u t}&=\frac{2}{2.5} \times 10=8 \mathrm{V} \\ V_{l t}&=-\beta_{l} V_{s a t} \end{aligned}
(when upper diode is ON, $\beta_{l}=\frac{2 \mathrm{k} \Omega}{4 \mathrm{k} \Omega}=\frac{1}{2})$
$=-\frac{1}{2} \times 10=-5 \mathrm{V}$
$V_{u t} \& V_{l t}$are upper and lower transition voltage.
 Question 6
Consider the following two statements:

Statement 1: A stable multi-vibrator can be used for generating square wave.
Statement 2: B stable multi-vibrator can be used for storing binary information.
 A Only statement 1 is correct B Only statement 2 is correct C Both the statements 1 and 2 are correct D Both the statements 1 and 2 are incorrect
GATE EC 2001   Analog Circuits
There are 6 questions to complete.