The transient junction temperature rise and secondary breakdown in transistor

The secondary breakdown is most serious problem in transistor failure, especially in switching circuit with inductive load. In this paper, is analyzed the secondary breakdown by thermal conception. The transient junction temperature rise is determined by the transient thermal resistance measured by a new method suggested in this paper. Then, the secondary breakdown in base open condition is analyzed by increase of the collector saturation current ICEO due to junction temperature rise. And the delay time of secondary breakdown that is the time for I to increase by 120% as much as initial collector current is calculated for germanium transistor. On the other hand, the experiment to measure the delay time is made under the same condition as in calculation, and it is shown that the result agrees with the calculated result. Furthermore, the secondary breakdown in base reverse bias condition and turnover mechanism of collector output characteristic in switching circuit with inductive load are explained by current crowding effect. And the secondary breakdown in silicon transistor is also supposed to be caused by the same thermal mechanism. Finally, the temperature characteristic of secondary breakdown is obtained and it is also analyzed by increase of ICEO due to junction temperature rise.