The Computerized use of Transient Thermal Resistance to Avoid Forware Biased Second Breakdown in Transistors

The power handling capability of any transistor is limited by its peak junction temperature. Equally as important as the more familiar ICBO thermal runaway is a second, thermally related, phenomenon called forward biased second breakdown (S/B). Much has been written on S/B (see Ref. 1 for a thorough description and bibliography) but it is sufficient here to say that S/B is a potentially destructive phenomena that can occur in any bipolar transistor when the energy absorbed exceeds a critical value and creates a hot spot within the pellet. If the temperature of the hot spot is left unchecked, it will eventually cause the space-charge layer to collapse resulting in the transistor assuming a low resistance state.