Home > Electronic Tutorials > Digital Circuits Tutorial > Multivibrators Tutorial

Digital Circuits - Electronic Tutorials

Multivibrators Tutorial


Multivibrators (sometimes called FLIP-FLOPS) have two "cross coupled" transistors, say TR1 and TR2.
This causes TR1 to be on (conducting) and TR2 off.
They can be made to reverse states, with TR1 turning off and TR2 turning on.
The states of the transistors can be indicated using a lamp for each transistor.

THE ASTABLE is continually changing state.
The lights flash alternately on and off.
This is because it has two UNSTABLE states and is changing automatically from one to the other.
The duration of these states is determined by two RESISTOR/CAPACITOR TIME CONSTANTS.
Changing the values of the time constants alters the flashing rate.

THE MONOSTABLE has one unstable and one stable state.
It rests in the stable state, waiting for an external pulse.
When a pulse arrives it changes to the unstable state.
It stays in the unstable state for a time determined by an RC time constant.
It then falls back into the stable state and waits for another pulse.
This means that the lights wait in the stable state, one on, the other off.
When the pulse arrives they change state for a while and then fall back to the waiting state.

THE BISTABLE has two stable states.
It waits in one state for an external pulse.
When the pulse arrives it changes into the other stable state waiting for another pulse.
If another pulse never arrives it will wait forever.
The lights change over on the arrival of each pulse.

Note: To report broken links or to submit your projects please send email to Webmaster