A multivibrator is an electronic circuit used to implement a variety of simple two state systems such as oscillators ,timers and flip-flops . It is characterized by two amplifying devices (transistors ,electron tubes or other devices ) cross coupled by resistors or capacitors . The name “multivabrator” was initially applied to the free running oscillator version of the circuit because its output waveform was rich in harmonics .
Multivibrator are a group of regenerative circuits that are extensively used in timing application .
multivibrator is classified as (Types) :
- Astable multivibrator
- Mono stable miltivibrator
- Bistable multivibrator
1. Astable multivibrator
Astable multivibrator
It is known as free runing multivibrator .it is also called as squre wave generator . the circuit has two quasi -stable states (no stable state ).Thus three is an oscillation between two state and no external signals are required to produce change in state .astable circuits are used to generate squre wave .for example clock generators in digital system.
2. Mono stable multivibrator
Mono stable miltivibrator
The mono stable or one -shot multivibrator generates a signal pulse of specified duration to each external trigger .As its name implies only one stable state exist .Application of each trigger causes a change to the quasi stable state. The circuit remains in the quasi stable state for a fixed interval of time and then reverts to its original stable state . In fact an internal trigger signal is generated which produces the transition to the stable state. Usually the charging and discharging of capacitor provides this internal trigger signal.
3. Bistable multivibrator
Bistable multivibrator
It is called as bistable latch of flip flops. Schmitt trigger is another bistable circuit important property of a bistable multivibrator is that it maintains a given output voltage level unless an external signal is applied .Application of external signal causes a change of state and this output level is maintained indefinitely until a secondtrigger is applied .Thus a bistable multivibrator requires two external trigger before it returns to its initial state.