Overcurrent protection circuit for power transistor

In an electronic circuit with a protected transistor having base and emitter electrodes with an emitter-base junction therebetween, having a collector electrode, and being connected for receiving a base drive current and an emitter-to-collector potential, an overcurrent protection circuit for said protected transistor comprising:

• a reference transistor having base and emitter electrodes with an emitter-base junction therebetween, having a collector electrode, and having said protected transistor thermally coupled therewith for tracking the operating temperature of said reference transistor to that of said protected transistor;
• means connecting said reference transistor for conducting a predetermined level of current through a collector-to-emitter path thereof;
• differential comparator means connected to compare the emitter-to-base potential of said protected transistor to that of said reference transistor for providing an indication of an overcurrent condition with regard to said protected transistor whenever its emitter-to-base potential increases by specified amount in comparison to the emitter-to-base potential of said reference transistor;
• and
• means responsive to said indication of an overcurrent condition for limiting further increase in the base drive current available to said protected transistor.