A Charge Control Relation for Bipolar Transistors

A basic concept of charge control theory is that the controlled current (collector current) equals controlling charge (base charge) divided by a transit time. 1 This paper presents an additional relation which links base charge and collector current with junction voltages. The validity of this relation is subject only to minor restrictions. When these are met the relation holds even under high-level injection conditions. Section II presents a derivation of the new charge control relation. Equation (15) states the principal result. The discussion in Section I I I points out the significance of this relation for bipolar transistor models. I I . DERIVATION Consider a one-dimensional transistor of pnp polarity. The hole current density is given by jp = quEp - qDp' (1)