6. The bistable circuit

The others fundamental circuits of the digitals technique are the circuits which can assume (and maintain steadily) one or another of 2 possible states, commonly noted like flip-flop.

Between the different versions possible, comes that one in which the state changing is provoked from the forehead of wave of an impulse.

The circuit summarizes the departure situation every 2 impulses, this is the base of every count device .

It's also commonly defined like T-flip-flop or frequency divisor.

The typical circuit, related in fig.6, is piloted by an push-button (which can be substituted by a transistor, for example the final stage of the precedent oscillator), which is closed momentarily: for each close corresponds the state changing of the exit (represented from the TR2 collector tension, this is Vc2).

To the current application, a small circuital asymmetry takes one of the 2 transistor in the conduction (let's suppose TR2), while the another one is interdict.

This provokes the condenser charge in the TR2 base circuit, while that one of the circuit of TR1 base remains empty.

Since with the push-button P opened the 2 condensers connected at this one charge, its close provokes an forced interdict of the both transistor. But for the fact which just a base condenser is empty, the transistor opening effect provokes the charging of this one, with the consequent forcing in relative transistor conduction.

In practical, at each P closing impulsive there is a status exchange between the both transistor (isn't simulated the effect of the condenser charge).

Fig.6 Bistable circuit simulation (T-flip-flop).