Transistor Switching Analysis

Citation

Mead, Carver A. (1960) Transistor Switching Analysis. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0Q5Z-KA62. https://resolver.caltech.edu/CaltechETD:etd-05182006-084112

Abstract

With the widespread application of junction transistors in switching applications, the need for a general method of analysis useful in the region of collector voltage saturation has become apparent. Linear equivalent circuits using lumped elements have long been used for small signal calculations of normally biased transistors, but a comparable method for saturated transistors has been lacking. Recently Linvill (3) proposed the method of lumped models which allows the analysis of complex switching problems with the ease of linear circuit calculations. In Part I the method is shown to be equivalent to a well-known linear equivalent circuit under normal bias conditions. Examples of the application of the method and the use of approximations are drawn from practical circuit problems. Emphasis is placed upon the understanding of the physical phenomena involved, a necessary prerequisite to intelligent circuit design. In Part II the operation of transistors at relatively large collector currents is considered. Several effects which contribute to non-linear operation are analyzed. It is shown that at both high and low injection levels, a decrease in current gain is to be expected as a result of the self bias cutoff effect.

Emitter efficiency is shown to be important at high levels because of its contribution on the self bias effect.

The operation of both alloy and diffused base transistors as saturated switches is discussed, with particular reference to the nonlinear effects. Theoretical expressions are derived for the saturation voltage as a function of collector and base current for both types.

Thesis Files