# Multivibrator MCQ

1. Monostable multivibrator may be used to generate

1. sweep voltage
2. pulses
3. sinusoidal voltage
4. sweep current

A monostable multivibrator may be used to generate pulses whereas an Astable multivibrator may be used to generate a square wave.

2. A 1 μs pulse can be converted into a 1 ms pulse by using

1. A monostable multivibrator
2. An astable multivibrator
3. A bistable multivibrator
4. A J – K flip-flop

• Given that the 1 μs pulse is converted into a 1 ms.
• This is pulse widening. This can be achieved with the help of the monostable multivibrator.

3. The pulse width out of one-shot multi-vibrator increases when the

1. Supply voltage increases
2. Timing resistor decreases
3. UTP decreases
4. Timing capacitance increases

The pulse width of a one-shot multivibrator depends on the formula,

τ = 1.1 RTCT

Hence, the timing cycle of the monostable multivibrator is determined by the timing capacitor, CT, and the resistor RT until it resets or returns to the original state.

It remains in the original stable state indefinitely until another input pulse or trigger signal is received. Hence, it has only one stable state.

4. Which of the following is not the other name for the Monostable Multi-vibrator circuit?

1. Univibrator
2. One-shot
3. Gating circuit
4. Square wave generator

Square wave generator:

• It is defined as an oscillator that gives the output without any input.
• This generator is used in digital signal processing and electronic applications.
• The square wave generator is also known as an Astable multivibrator or free-running.
• The frequency of the square wave generator is independent of the output voltage.

​So, a square wave generator is an astable multivibrator and not monostable multivibrator.

5. Which among the following multivibrators is unstable in any state?

1. Astable multivibrator
2. Bistable multivibrator
3. Monostable multivibrator
4. Both astable and bistable multivibrator

• An Astable multivibrator is such a circuit that it automatically switches between the two states continuously without the application of any external pulse for its operation, i.e. it is unstable in any state.
• As this produces a continuous square wave output, it is called a free-running multivibrator.

6. The formula for the frequency of a 555 astable multivibrator

1. 1.44/(RA + 2RB)C
2. (RA + 2RB)c/1.44
3. (RA + 2RB)C
4. None of the above

Time period high of 555 timers is given by

THigh = 0.693(RA + RB) C

Tlow = 0.693 RBC

Thus, total time period T is given by

T = THigh + Tlow

T = 0.693 (RA + 2 RB) C

f = 1/T =  1.44/(RA + 2RB)C

7. Schmitt trigger can be used as a

1. Comparator
2. Square wave generator
3. Flip flop
4. All of these

• A Schmitt trigger is basically an inverting comparator circuit with positive feedback.
• The purpose of the Schmitt trigger is to convert any regular or irregular-shaped input waveform into a square wave output voltage or pulse.
• Thus, it can also be called a squaring circuit and can be used as a square wave generator.
• When the input is below a different (lower) chosen threshold, then the output is low, and when the input is between the two levels, the output retains its value.
• This dual-threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable multivibrator (latch or flip-flop).

8. The bistable multivibrator

1. has two stable states
2. has one stable state
3. is free running
4. none of the above

A Bistable multivibrator has both the two states stable. It requires two trigger pulses to be applied to change the states. Until the trigger input is given, this multivibrator cannot change its state.

9. A monostable multivibrator is frequently used

1. in memory and timing circuits
2. for regeneration of distorted waves
3. in counting circuits
4. for producing triangular waves

Answer.2. for regeneration of distorted waves

• The Monostable Multivibrator circuit has only ONE stable state making it a “one-shot” pulse generator
• Monostable multivibrators can consider as triggered pulse generators
• It is used as delay and timing circuits
• It is used for the generation of clock pulse
• It is used for ​the regeneration of distorted waves
• It is also used in analog systems to control an output signal frequency

10. A monostable multivibrator requires

1. no driving pulse for generation of output cycles
2. one driving pulse for each output cycle
3. two driving pulses for each output cycle
4. four driving pulses for each output cycle

Answer.2. one driving pulse for each output cycle

• Monostable multivibrator has a stable state and a quasi-stable state. This has a trigger input to one transistor. So, one transistor changes its state automatically, while the other one needs a trigger input to change its state.

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