Properties and Their Applications of Current Gain Variation Preceding to the Second Breakdown in Power Transistors


IEICE TRANSACTIONS (1976-1990)   Vol.E62   No.12   pp.858-862
Publication Date: 1979/12/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Semiconductors

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Properties of current gain variation in n+ -p -n -n+ power transistors preceding to the thermal mode second breakdown and their applications to evaluate the resistance of second breakdown are presented. The characteristics of current gain in power transistors with junction temperature and current density are examined under high voltage operating conditions which are sufficient to generate thermal instabilities and second breakdown. Applying these properties, processes of generation of thermal instabilities and second breakdown in power transistors are investigated. Predictions of second breakdown initiation are made by monitoring the variation of the base current under the constant voltage and constant current conditions at the collector-base junction. The waveforms of the base current under these conditions show the typical changing point just before the second breakdown initiation. It is concluded that, the characteristic phenomena are related to the variation of the current gain, and the changing point corresponds to the generation of thermal instabilities. The forward biased second breakdown resistance can be measured without damage or degradation of the sample transistors, if the supplied power has been removed when the base current reaches the changing point.