A multivibrator is an electronic circuit that rapidly switches because of positive feedback between multiple states. The switch’s output is harmonic. Three types of multivibrator circuits are used in industry today: astable, monostable, and bistaple.

Types of Multivibrators

The three multivibrator types are:

Astable Multivibrator – The circuit is not considered stable in either of the two possible states. It continually switches from one of the potential states to the other, but does not require a clock pulse or other input in order to operate.

Monostable – One of the circuit’s two states is considered transient and the other stable. A trigger of some type causes the circuit to change to the unstable state and it becomes stable again after a predetermined time frame. These circuits create a timing period of finite length that an event triggers.

Bistable – These circuits are stable in both possible states and external stimuli can flip them from one state to the other. They are also considered to be a “flip-flop” circuit type.

The Multivibrator’s Primary Components

There are two main components in every multivibrator: the bistable circuit and two passive networks that are connected in a basic feedback loop. The networks in the circuit can either be monostable (resistive), astable (resistive-capacitive), or bistable. They are used in a number of systems where a timed interval or a square wave is required, including early television systems. H. Abraham and E. Block described the first multivibrator circuit in 1919.

What is the 555 Timer?

Signetics developed the 555 timer in 1971. This common multivibrator application is an integrated circuit and remains in production today. It operates in bistable, astable, or monostable modes based on how it is connected and how the circuit’s external components are arranged. The timer is used in a number of applications today, including quartz watches, AM radio receivers, cell phones, pagers, audio-frequency equipment, music synthesizers, and GPS wireless receivers and transmitters.