Large-Signal Behavior of Junction Transistors

TLDR

The junction transistor functions as a switch with key characteristics of open impedance, closed impedance, and switching time, and its transition between states involves minority carrier storage effects. The study presents a generalized two‑terminal‑pair theory for junction transistors applicable across all DC operating regions. The theory derives open and closed impedances from measurable parameters such as emitter/collector saturation currents and alpha values, and analytically models the transition using alpha cut‑off frequencies.

Abstract

In the consideration of the junction transistor as a switch there are three characteristics of primary interest, the open impedance, the closed impedance, and the switching-time. A generalized two-terminal-pair theory of junction transistors is presented which is applicable, on a dc basis, in all regions of operation. Using this theory, the open and closed impedances of the transistor switch are expressible in terms of easily measurable transistor parameters. For the ideal transistor these parameters are the saturation currents of the emitter and collector junctions and the normal and inverted alphas. The transition of the transistor switch from open to closed, or vice versa, is discussed, including the effects of minority carrier storage. This transition can be expressed in analytic form in terms of the alphas and the normal and inverted alpha cut-off frequencies.