# Multivibrators

#### BobTPH

Joined Jun 5, 2013
4,253
I have only ever heard multivibrator applied the two transistor circuit with the inputs cross connected to the outputs. Depending on whether a resistor or capacitor is used in each of these connections it is astable, bistable, or monstable.

Bob

#### AnalogKid

Joined Aug 1, 2013
9,621
With a giant load of respect, I disagree with part of Mr Chips definition. A multivibrator is first and foremost an oscillator. That was the original invention, and that's why "vibrate" is in the name. Monostable came later, and really is just the classic circuit with one capacitor missing. Both of these are variations of the same theme - one way to view the classic multivibrator circuit is two monostables in series, triggering each other.

That another variation of the circuit can do something completely different is nice, but it doesn't change the original intent, or the way that intent has held through the decades. Call that circuit a bistable? Sure. Bistable multivibrater? I just don't see it.

ak

Last edited:

#### KL7AJ

Joined Nov 4, 2008
2,229

So, without having really studied multivibrators, I was somewhat taken aback the other day from coming to an understanding that a S R latch is a form of multivibrator.

I believe a regular motor starter circuit, where pressing the start button latches power to the motor and the stop button resets to the initial condition is a S R latch circuit.

That would make this motor circuit a multivibrator circuit.

Because I read "Any digital circuit employing feedback is called a multivibrator." I always assumed the word "multivibrator", referred to a circuit that was a kind of oscillator. Seems it does not have to be.
Digital terminology is indeed a bit misleading. A multivibrator can be stable, astable, or monostable (a one-shot).

Eric

#### richard3194

Joined Oct 18, 2011
162
Originally, the multivibrator is an oscillator. It's the original flip-flop when you think about it -if you see the output in terms of flip and flop. The output is astable flip flop because neither flip or flop is stable.

We also have a circuit whose output is flip flop, but where only one of the states is stable. We call that the monostable mutivibrator. It's not an oscillator though, it has to be triggered into the unstable state. It is a kind of vibrator, but it's a triggered one. It does output a flip and flop it is a flip flop circuit.

Also, we have the bistable flip flop. Here the output state depends on a trigger signal, and both states can be stable. Is this a vibrator? Well, it is if you consider that the outputs will change, they are not expected to remain stable all the time. So, it is a vibrator of sorts, as the astable and monostable flip flop circuits are.

Are they all multivibrators? Yes, if you consider the output in terms of flip and flop. Flip flop is a vibration.

My 2 cents.

Last edited: