Table of Contents
Introduction to Multivibrator
Multivibrator is wave shaping circuit which generates non sinusoidal waves called Multivibrator. It can generate square wave rectangular wave triangular wave or saw tooth wave. These belongs to a family of oscillator know as Relaxation oscillators. A 180° phase shift between the amplifier’s input and output has already been explored. The overall phase shift will be 360° if two amplifier stages are used. Positive feedback will come from feeding the output of the second stage into the input of the first. The arrangement is shown by a block diagram.
The circuit has only two states. (ON or OFF). State of the circuit depends upon circuit conditions. The feed back is such that it drives one transistor (Q) into saturation region (ON state) and the other transistor (Q) in to cut region (OFF state). The state of transistor is reversed after some time depending upon circuit conditions.
States of Multivibrator
A multivibrator is an electronic circuit that generates two alternating output states. These states can be either stable or quasi-stable, meaning that they can last for a finite period of time before changing to the other state.
1. Stable state
A stable state is a state in which the circuit remains until an external trigger is applied. In a bistable multivibrator, for example, there are two stable states. Once the circuit is in one of these states, it will remain there until it receives a trigger to switch to the other stable state.
2. Quasi-stable state
A quasi-stable state is a state that lasts for a finite period of time before changing to the other state. In an astable Multivibrator, for example, there are no stable states, and the circuit continuously switches back and forth between two quasi-stable states. In this case, each quasi-stable state is held for a short period of time before switching to the other state.
3. Astable state
An astable state is a state in which the circuit continuously switches back and forth between two quasi-stable states without the need for any external trigger. As mentioned earlier, this is the state of an astable multivibrator, which continuously generates a periodic waveform.
In summary, the stable states of a multivibrator are states that remain until an external trigger is applied, while the quasi-stable states are states that last for a finite period of time before changing to the other state. An astable state is a state in which the circuit continuously switches back and forth between two quasi-stable states without any external trigger.
Classification of Multivibrator
1. Astable Multivibrator
A circuit which generates square wave on it’s own (without external triggering pulse) is called Astable multivibrator or free running multivibrator. It does not have any stable state Circuit keeps on changing it’s state from ON to OFF and then reverses it’s state after some time The time period of change to state depends upon circuit components. No external triggering pulse is required to change the state.
In simply we can say that an astable multivibrator has no stable states; it continuously switches back and forth between two quasi-stable states, with no external input needed. This circuit is commonly used in applications that require a periodic output waveform, such as in oscillator circuits.
2. Monostable Multivibrator
A mulitivibrator in which one transistor is always conducting i.e. remains in ON state and the other is non conducting means OFF state is called a monostable multivibrator. Mono means remains in one. So monostable contains one state. On the application of an external triggering pulse, the multivibrator changes state form stable state to quasistable state. After certain time, determined by the circuit conditions, the circuit automatically comes back to it’s original state. It remains in this stable state till another triggering pulse is applied.
3. Bistable Multivibrator
A multivibrator in which both the states are stable is called bistable multivibrator. Both the states of bistable multivibrator will remain in a stable region as long as an external pulse is applied to change it’s state. When external pulse is applied, it changes its state form one stable state to the other stable state. It will return to its original stable state only when another external pulse is applied to the circuit. The two stable stages are known as Latches and flip-flops for use in sequential circuits. This circuit is used for generation of pulses, storage of information in binary form and counters etc.
In simply we can say that a bistable multivibrator has two stable states and can be in either one of them until an external trigger signal is applied. Once triggered, the circuit will switch to the other stable state and remain in it until another trigger signal is applied. This circuit is commonly used as a memory element or as a basic building block for more complex digital circuits
Summary
A multivibrator is an electronic circuit that generates two alternating output states, which can be either stable or quasi-stable. The two main types of multivibrator are the astable multivibrator, which continuously switches back and forth between two quasi-stable states, and the bistable multivibrator, which has two stable states and can be triggered to switch between them
Frequently Asked Questions (FAQs)
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What are the types of multivibrator?
The three main types of multivibrator are astable, monostable, and bistable multivibrator. Astable multivibrator produce a continuous oscillating output waveform, while monostable multivibrator produce a single output pulse in response to a triggering input. Bistable multivibrator have two stable states and can be triggered to switch between them.
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What are the applications of multivibrator?
Multivibrators have a wide range of applications in electronics, including as clocks, timing circuits, frequency dividers, and pulse generators. They are also used in digital circuits, analog-to-digital converters, and other applications where a stable oscillating waveform or pulse is needed.
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Why astable multivibrator is known as free running multivibrator?
A multivibrator that generates square wave of its own is known as astable multivibrator. It has no stable state. There are two quasi-stable states. The circuit changes automatically form one quasi-state stare to another without any external triggering pulse. It does not require any external pulse for its operation so it is known as free running multivibrator.
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