4. The monostable circuit

The simulation can be applied also in the configurations where the transistor function at everything or nothing in state of interdiction (opened) or in the saturation (closed) or rather in these cases is more simple to study the behavior, determine first the values in the stables conditions and raccordandoli then with the dynamics equations (exponentials, functions of the time constants).

The first case which can be be taken in consideration is that one of the monostable circuit, in which the momentary the chiusura of a push-button (P) provokes the chiusura of the transistor of the exit (TR2) for a prefissabile time. This is a typical case of the temporizzatore used in the industrial automatism.

Fig.4 A circuit monostable (temporizzatore) simulation.

At the act of current, the condenser is charged practically at the current value through the resistance of TR2 collector, forcing in conduction TR1.

With TR1 closed, the TR2 base is maintained under the conduction threshold, so TR2 is opened.

If in this point P is close, the condenser tension becomes a negative polarization at TR1 base ( see the Vb1 graphic, azure-blue) which is proscribed, that is open.

At this point the TR1 collector resistance becomes the TR2 base resistance, which passes in conduction, and it remains (also when P releases), until the condenser isn't empty.

The graphics relate the process of the tension values calculated from the simulation program respective on the bases (Vb1, azure-blue and Vb2, magenta) and on the exit collector (Vc2, red).

Interesting practices could be the practice determination of the values by assign to the collector resistances (respectively Rc1 that becomes the Rb2 base resistance when TR2 leads, and Rc2 that determines the exit signal) or the relation research between the condenser value and the times of maintenance (adjustable then between a maximum and a minimum with the cursor).