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Ideal and Perfect Bipolar Transistor Models

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:

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

Doug Gingrich
Tue Jul 13 16:55:15 EDT 1999