As we have seen it is best considered as input parameter directly *input differential voltage* v_{D} rather than the individual voltage inputs present at the poles V_{+} and V_{-}.

There is also another aspect that should be considered to complete the mathematical model of the *Operational Amplifiers*.

What does happen when the model return a value exceeding the range of the power supply voltages?

Let assume that power supply voltages are:

and let assume that inputs are:

In this case *differential voltage input* is equal to:

and voltage output is equal to:

The output voltage exceeds V_{CC}!

Is it possible?

Certainly it isn't.

What happens is that voltage output V_{OUT} can not exceed V_{CC} or V_{EE} (it doesn't even reach them, but the difference is small and we assume that V_{OUT}'s limits match exactly to V_{CC} and V_{EE}).

The mathematical model changes and the curve becomes: