Abstract: The base-emitter junction of a bipolar transistor is first forward biased to place the transistor in a state of conduction and the forward bias is then removed. A discharge path is provided for the base-emitter capacitance of the transistor, this path including a source of reverse bias voltage for the base-emitter junction. A sensing circuit indicates when the base-emitter capacitance has discharged through the path sufficiently to permit the base-emitter junction to become reverse biased, which in turn indicates that the transistor has cutoff.

Abstract: An automated test set for determining the reverse biased second breakdown characteristics of a bipolar transistor without destroying or degrading the transistor under test (TUT). A source supplies current to the TUT through an inductor. The amplitude of this current increases in predetermined increments. After each current amplitude increase, the base-emitter junction of the TUT is reverse biased and the source is disabled. If enough energy is stored by the inductor to cause second breakdown, this breakdown is detected and the test is terminated. Otherwise, the test continues until the test current reaches a predetermined maximum amplitude, at which time the test is terminated. Damage to the TUT is avoided by restricting the stored energy to levels high enough to cause second breakdown but low enough that the remaining energy does not cause thermal damage.