Mitsubishi Denki Kabushiki Kaisha

Masanori Inoue

Ikunori Takata

The present invention is directed to effectively prevent 'load short-circuit breakdown' of a power Darlington transistor. When a potential different between a base BX and emitter E at a final stage of a power Darlington transistor (20) is at a specified level of voltage determined by base-emitter forward voltage of a protective bipolar transistor (32), the protective bipolar transistor (32) turns on, and accordingly, base current I.sub.B at an initial stage of the power Darlington transistor (20) is bypassed to the emitter E at the final stage. Hence, excessive rising of collector current I.sub.C of the Darlington transistor (20) is suppressed, and 'load short-circuit breakdown' is prevented. The potential difference does not depend upon the number of stages of the Darlington transistor nor temperature, and therefore, it is facilitated for Darlington transistors of various numbers of stages to design a short-circuit protective circuit to ensure a specified bypass operation in the whole range of working temperature.

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Fukuoka, Japan

Masanori Inoue