Cherry Semiconductor Corporation

John G Metro

Walter S Gontowski, Jr

Denis P Galipeau

Steven S Yole

A transistor overcurrent protection circuit using an error amplifier to make a voltage comparison between a threshold voltage and the collector voltage of a current sensing transistor. The current sensing transistor is arranged in a circuit such that the collector current of the current sensing transistor is a measure of the collector current of an output transistor. A driver transistor has its emitter connected to the base of the output transistor. A source of control current to the drive transistor is coupled to the output of the error amplifier. When the collector voltage of the current sense transistor falls below the threshold voltage, the error amplifier causes the control current to the drive transistor to be reduced so as to reduce the collector current of the output transistor.

Transistor overcurrent protection circuit

An oscillator integrated circuit is disclosed in which a predetermined current is reliably established through a discharge transistor by zener zapping appropriate circuit components. In accordance with an embodiment, a plurality of zener diodes are provided in parallel with a plurality of resistors and one or more is shorted out to achieve a predetermined discharge current. In accordance with a second embodiment, the multiplication factor of the discharge transistor is set by trimming its emitters through zener zapping to obtain a predetermined discharge current.

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Kingston, RI, United States of America

John G Metro