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1.	Given the circuit below, find the feedback factor.(a) 3(b) 1/3(c) 4(d) 1/4This question was addressed to me during an internship interview.This key question is from Different Types of Multivibrators topic in section Multivibrators of Analog Circuits
Answer» CORRECT option is (d) 1/4 The BEST I can explain: The feedback FACTOR is β = R1/R1+R2 β = 10k/30k+10k = 1/4.

2.	What is a square wave generator?(a) Flip-flop(b) Bi-stable multivibrator(c) Astable multivibrator(d) Monostable multivibratorThis question was addressed to me by my school principal while I was bunking the class.Asked question is from Different Types of Multivibrators topic in section Multivibrators of Analog Circuits
Answer» Right option is (C) Astable multivibrator For explanation: An astable multivibrator is one which does not have any STABLE state. It has two quasi-stable output states which keep toggling at regular intervals. The output waveform is thus a square wave and this circuit is also CALLED a square wave generator or a free running OSCILLATOR.

3.	In an astable multivibrator using an op-amp, the feedback factor is 0.5 and the supply voltage is ±12V. What are the quasi-stable output state and the input to the non-inverting terminal?(a) Quasi-stable output = ±12V, Input to non inverting terminal = ±12V(b) Quasi-stable output = ±6V, Input to non inverting terminal = ±12V(c) Quasi-stable output = ±12V, Input to non inverting terminal = ±6V(d) Quasi-stable output = ±12V, Input to non inverting terminal = 0VThe question was posed to me in an interview.Origin of the question is Different Types of Multivibrators topic in portion Multivibrators of Analog Circuits
Answer» The correct answer is (c) Quasi-stable output = ±12V, Input to non INVERTING terminal = ±6V The BEST EXPLANATION: Quasi-stable output = ±VSat = ± VSupply = ±12V Input to non inverting terminal = ±βVSat = ±6V.

4.	Given that the feedback factor of an astable multivibrator is 0.3, find the frequency of the output.(a) 22Hz(b) 20kHz(c) 20Hz(d) 40HzI have been asked this question by my college director while I was bunking the class.I'd like to ask this question from Different Types of Multivibrators in division Multivibrators of Analog Circuits
Answer» CORRECT answer is (c) 20HZ Easiest explanation: TO = 2RCln (1 + β/1-β) = 2RCln(1.3/0.7) = 2x10x4x10^-3x0.619 = 49.52ms f = 1/TO = 20Hz.

5.	What is the duty cycle of the output of an astable multivibrator?(a) 50%(b) 100%(c) 75%(d) 55%I got this question by my school principal while I was bunking the class.I'd like to ask this question from Different Types of Multivibrators topic in division Multivibrators of Analog Circuits
Answer» Correct option is (a) 50% The EXPLANATION is: An astable multivibrator is a SQUARE wave generator. Charging and discharging TIMES of the capacitor are equal and THUS the output waveform has a duty cycle of 50%.

6.	Consider the following circuit and find the time period of the output of the multivibrator.(a) 0.436 ms(b) 0.436 seconds(c) .5 ms(d) 5.22 secondsI have been asked this question in a national level competition.This question is from Different Types of Multivibrators in portion Multivibrators of Analog Circuits
Answer» The correct OPTION is (b) 0.436 seconds The explanation is: Since the TWO FEEDBACK RESISTORS are same, then β=0.5. Thus time period TO = 2RCln3 = 2x20x10x10^-3x1.09 = 436ms = 0.436 seconds.

7.	How can the duty cycle be changed for an astable multivibrator?(a) By adding another capacitor to the circuit(b) By adding diodes to the circuit(c) By adding an inductor to the circuit(d) The duty cycle cannot be changedI have been asked this question in my homework.This interesting question is from Different Types of Multivibrators in portion Multivibrators of Analog Circuits
Answer» Correct choice is (b) By ADDING DIODES to the circuit The best I can EXPLAIN: To generate a square wave of duty cycle other than 50%, diodes can be CONNECTED so that charging and discharging now occurs through these diodes. This thus CHANGES the time period as well as the duty cycle of the diodes.

8.	Given that the feedback factor is 0.6, find the time period of the circuit below.(a) 0.331 seconds(b) 0.303 seconds(c) 0.276 seconds(d) 0.606 secondsI had been asked this question by my college professor while I was bunking the class.My question is taken from Different Types of Multivibrators in division Multivibrators of Analog Circuits
Answer» Correct option is (B) 0.303 SECONDS Explanation: T = (RXC + RYC)LN(1+β/1-β) T = 22x10x10^-3xln(1.6/0.4) = 22x10x10^-3x1.38 = 0.303 seconds.

9.	The monostable multivibrator has one quasi-stable state and one unknown state.(a) True(b) FalseThe question was posed to me in quiz.The doubt is from Different Types of Multivibrators topic in division Multivibrators of Analog Circuits
Answer» Correct option is (b) False Easiest explanation: The MONOSTABLE multivibrator is a circuit whose output has one stable state and one quasi-stable state. If the trigger INPUT is not applied then output remains in the stable state INDEFINITELY and whenever the trigger is applied, the output enters the quasi-stable state. The output then CHANGES back to the stable state on its own after a short duration.

10.	For the given circuit, find the time period of the output waveform, given that the diode is used is of Silicon and the supply voltage being applied is ±15V.The feedback factor is 0.4.(a) 11.12 ms(b) 12.4 ms(c) 11.2 seconds(d) 5.6 msI got this question during an interview for a job.Query is from Different Types of Multivibrators topic in chapter Multivibrators of Analog Circuits
Answer» The CORRECT CHOICE is (a) 11.12 MS For EXPLANATION: T = RCln(1+Vγ/VSat/1-β) T = 10x2x10^-3xln((1+0.7/15)/0.6) = 20×10^-3ln(1.0467/0.6)=20×0.556×10^-3 T = 11.12 ms.

11.	Which of these is not a type of monostable multivibrator?(a) Schmitt trigger as a monostable multivibrator(b) Emitter coupled monostable multivibrator(c) Using an op-amp(d) 555 Timer as a monostable multivibratorI got this question in a job interview.Question is taken from Different Types of Multivibrators in section Multivibrators of Analog Circuits
Answer» The CORRECT CHOICE is (a) Schmitt trigger as a monostable multivibrator The best explanation: A Schmitt trigger circuit is a comparator circuit, ALSO called a regenerative comparator. It converts any waveform into a square wave. It is not a monostable multivibrator, unlike the other THREE options.

12.	How can a monostable multivibrator using IC 555 be used as a PWM generator?(a) If a diode is connected across the resistor RA(b) If a modulating signal m(t) is applied at the control pin(c) If the control pin is always kept high(d) It cannot be used as a PWM generator everI had been asked this question in an internship interview.Question is taken from Different Types of Multivibrators topic in portion Multivibrators of Analog Circuits
Answer» Right option is (c) If the control pin is ALWAYS kept high The explanation: A monostable MULTIVIBRATOR can be USED as a PWM generator if a modulating signal is applied to the control pin. The control pin is used to vary the voltage at the inverting node of the upper COMPARATOR. If unused, then the control pin is grounded through a capacitor.

13.	In the astable multivibrator using IC 555, it can be used as a voltage to frequency converter.(a) True(b) FalseI got this question in an online interview.I would like to ask this question from Different Types of Multivibrators topic in section Multivibrators of Analog Circuits
Answer» CORRECT choice is (a) True Easiest explanation: An astable MULTIVIBRATOR can be easily used as a voltage CONTROLLED oscillator or as a voltage to frequency converter if a CONTROL voltage is applied to the control pin of the IC. The control pin is usually grounded through a capacitor if unused.

14.	Find the approximate frequency of output waveform of a monostable multivibrator given that RC = 20×10^-3 and feedback factor = 0.3.(a) 200Hz(b) 142Hz(c) 233Hz(d) Can’t be found out without supply voltage valueThis question was addressed to me in final exam.The origin of the question is Different Types of Multivibrators topic in chapter Multivibrators of Analog Circuits
Answer» RIGHT CHOICE is (b) 142Hz The best explanation: T = RCln(1/1-β) T = 20×10^-3 x ln(1/0.7) = 20×0.35×10^-3 = 7ms f = 0.142 KHZ = 142 Hz.

15.	Given that the charging current of capacitor is constant in a monostable multivibrator using IC 555, then find the type of output waveform, type of capacitor voltage waveform and the time period of output.(a) The capacitor waveform is a ramp, the output waveform is sinusoidal, the time period is \(\frac{2.C.VCC}{3.I}\)(b) The capacitor waveform is a ramp, the output waveform is a pulse, the time period is \(\frac{2.C.VCC}{3.I}\)(c) The capacitor waveform is a ramp, the output waveform is a pulse, the time period is \(\frac{C.VCC}{3.I}\)(d) The capacitor waveform is a ramp, the output waveform is a ramp, the time period is \(\frac{2.C.VCC}{3.I}\)I have been asked this question during an interview.Enquiry is from Different Types of Multivibrators topic in section Multivibrators of Analog Circuits
Answer» The correct CHOICE is (b) The capacitor waveform is a ramp, the output waveform is a pulse, the time period is \(\FRAC{2.C.VCC}{3.I}\) Easy EXPLANATION: If a constant charging current is APPLIED through the capacitor, the output is a pulse, while capacitor voltage is a ramp. Time period of ramp/pulse = TO = 2VCCxC/3I.