A nondestructive method for the determination of forward-biased safe-operating-area limits for power transistors

It is proposed that the limit of thermal instability replace the traditional limit of second breakdown for the safe-operating-area limits of power transistors. A nondestructive method for measuring the limit of thermal instability is described. The relationships between thermal instability, stable hot spots, and second breakdown are reviewed and it is shown that stable hotspot operating conditions can exist within the traditional safe operating area based upon second breakdown. The proposed safe-operating-area limit is shown to exclude these hot-spot operating conditions. The effect of thermal resistance on the thermal instability limit is briefly discussed.