What is a Multivibrator? 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 bistable.
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.
Types of Multi-Vibrators
a. Monostable Multi-vibrator: A monostable multivibrator is the type of multivibrator circuit whose output is in only one stable state. It is also known as the one-shot multivibrator. In a monostable multivibrator, the output pulse duration is determined by the RC time constant and is given as 1.11*R*C
b. A Stable Multi-vibrator: A stable vibrator is a circuit with an oscillating output. It doesn’t need any external triggering, and it has got no stable state. It is a type of regenerative oscillator.
c. Bistable Multi-vibrator: A bistable vibrator is a circuit with two stable states: high and low. Generally, a switch is required for toggling between the high and low state of the output.
Bistable multivibrator can be used as a bi directional switch. ie, as an ON and OFF switch. One stable state implies to ON and the second to OFF.
Monostable Multivibrator can be used to simply trigger a circuit for a particular input. ie, in circuits involving Microcontrollers sensing particular parameters (touch, humidity etc.). Thus making the circuit respond to the inputs.
Astable multivibrators can be used as oscillators ie, can be used to generate customized frequencies by proper design of circuit. Mostly they can be used to generate clocks for microcontroller or microprocessor circuits.
Important terms of Multivibrators
Duty Cycle: duty cycle is defined as the ratio of pulse duration to pulse period.
he pulse duration is τ; this is how long the pulse remains high (amplitude=1 in the figure). The pulse period is T; this is the duration of one complete cycle and is just the inverse of the frequency in Hz ( f = 1/T ).
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