Measurements of power transistor thermal instabilities, stable hot-spots, and second-breakdown

The relationships of thermal instability, stable hot spots, and second breakdown in power transistors are discussed. A rationale is also given for using thermal instability as opposed to second breakdown as the specified limit of safe operation for power transistors. It is shown that the limit of thermal instability can be accurately predicted and the simple device measurements required to do this are described. A rapid, easy, nondestructive test is also described for experimentally determining this limit.