Types of Multivibrator

Types of Multivibrator

There are three types of multivibrator circuits in use, namely, a) Bistable multivibrator b) Monostable multivibrator c) Astable multivibrator

Let us see the basic concept behind the operation of these three types of multivibrators.

1. Bistable Multivibrator

As the name suggests, the bistable multivibrator has two stable states. The multivibrator can exist indefinitely in either of the two stable states. It requires an  external trigger pulse to change from one stable state to another. The circuit remains in one stable state unless an external trigger pulse is applied.

Key Point The bistable multivibrator is also known by variety of other names as Eccles-Jordan circuit, trigger circuit, scale-of-2 toggle circuit, flip-flop and binary.

The bistable multivibrator is used for the performance of many digital operations such as counting and storing of the binary information. This multivibrator circuit also finds an application in the generation and processing of pulse-type waveforms.

2. Monostable Multivibrator

The monostable multivibrator has only one stable state. The other state is unstable referred as quasi-stable state. When an external trigger pulse is applied to the circuit, the circuit goes into the quasi-stable state from its normal stable state. After some time interval, the circuit automatically returns to its stable state. The circuit does not require any external pulse to change from quasi-stable to stable state. The time interval for which the circuit remains in the quasi-stable state is determined by the circuit components and can be designed as per the requirement.

Key Point The monostable multivibrator is also known by variety of other names such as one-shot, single-shot, a single cycle, a single swing, a single step multivibrator or a univibrator. It is also called gating circuit or delay circuit.

The circuit is used to generate the rectangular waveform and hence can be used to gate other circuits hence called gating circuit. The time between the transition from quasi-stable state to stable state can be predetermined and hence it can be used to introduce time delays with the help of fast transition. Due to this application, it is also called delay circuit.

3. Astable Multivibrator

The astable multivibrator has both the states as quasi-stable states. None of the states is stable state. Due to this, the multivibrator automatically makes the successive transitions from one quasi-stable state to other, without any external triggering pulse. The rate of transition from one quasi-stable state to other is determined by the circuit components.

Key Point As this multivibrator does not require any external pulse for the transition, is called free running multivibrator.

The astable multivibrator is nothing but an oscillator. It is used as the generator of square waves. As it requires no triggering it is used as a basic source of fast waveforms.

Both monostable and astable multivibrators find extensive application in pulse circuitry. 

Review Question

1. What is a multivibrator circuit ? What is its use ? State its types.