A quantitative study of emitter ballasting

Many workers have studied the effects of emitter ballast resistors, RE, on the uniformity of current distribution and the protection against hot spots and second breakdown. These studies have been either entirely experimental, establishing empirical limits on RE, or semi-analytical, assuming isothermal junction behavior. Neither of these approaches is adequate for some power transistors where large currents and bias voltages exist simultaneously, giving rise to high levels of dissipation. In particular, microwave power transistors fall into this category where in addition to the non-isothermal behavior of the emitter-base junction, the gain and efficiency degradation by REdictates a better study of emitter ballasting.