By ignoring and we can define a simplified AC model
for the transistor (*perfect* transistor) that is independent of
the circuit configuration:

There is no PN voltage drop in these equations since it is a DC effect.

Since is typically 100 times larger than we can make the
approximation .
An *ideal* transistor is defined such that and hence
.
When the effects of cannot be ignored, we can use the perfect
transistor model as described by the two equations above.
On a circuit diagram can be added directly to the ideal
transistor symbol.

The ideal transistor model has the following two working rules:

- The base and emitter are at the same AC voltage ( ). They differ only by a constant DC potential .
- The collector current is equal to the emitter current and proportional to the base current ( and ).

Tue Jul 13 16:55:15 EDT 1999