Electrical Characteristics of Power Transistors

The following electrical characteristics of a group of power transistors whose collector dissipation is in the region of 20 watts have been measured: the small-signal current amplification as a function of emitter current, the cutoff frequency as a function of emitter current and collector voltage, and the decrease of current amplification with increasing frequency. All these measurements were made in both common-base and common-emitter configuration. The results were compared with the theory developed for low-power transistors by Shockley, Rittner, Webster, and others, and it was found that for the frequency-dependent parameters, the agreement was quite good, but that differences exist in the case of those which are a function of current. This leads to the conclusion that further work must be done on the theory of junction power transistors.