Composite transistor device with over current protection

Claim 2

A composite transistor device with over-current protection comprising: a power transistor and an auxiliary transistor thermally coupled to each other, each having a collector electrode, each having a base electrode which base electrodes are interconnected, and each having an emitter electrode which emitter electrodes are interconnected; a connection between the collector electrodes of said power and said auxiliary transistors; means for detecting when the collector current flow of said auxiliary transistor flowing through said connection exceeds a predetermined value thus to provide a signal indicative of an over-current condition; and means for clamping the potential appearing between the base and the emitter electrodes of said power transistor in response to said signal indicative of an over-current condition.

Claim 3

A device as claimed in claim 1 wherein said means for detecting when the collector current flow of said auxiliary transistor flowing through said connection exceeds a predetermined value thus to provide a signal indicative of an over-current condition comprises: a resistive element connected between the collector electrodes of said power transistor and said auxiliary transistor and; a complementary transistor being of opposite conductivity type to said power transistor and said auxiliary transistor, having an emitter and a base Electrodes respectively connected to the collector electrode of said power transistor and to the collector electrode of said auxiliary transistor, and having a collector electrode for providing said signal indicative of an over-current condition.

Claim 4

A device as claimed in claim 2 wherein said means for clamping the potential appearing between the base and emitter electrodes of said power transistor comprises: a clamping transistor being of the same conductivity tyep as said power and said auxiliary transistors, having a collector and an emitter electrodes respectively connected to the base and emitter electrodes of said power transistor, and having a base electrode connected to receive said signal indicative of an over-current condition.

Claim 5

In combination: four transistors, each having base, collector and emitter electrodes, the first and second of said transistors connected base electrode-to-base electrode and emitter electrode-to-emitter electrode, the first and second and third of said transistors being of one conductivity type and the fourth of another conductivity type; a current sensing element connected to the collector of said first transistor for sensing the collector current of said transistor; the emitter-to-collector path of said third transistor being connected across the emitter-to-base path of said first transistor; the emitter-to-base path of said fourth transistor being connected across said current sensing element in a direction to produce emitter-to-base current flow in said fourth transistor when the current flow in said sensing element exceeds a given value; and the collector electrode of said fourth transistor connected to the base of said third transistor for delivering the collector current of said fourth transistor to the base-emitter path of said third transistor.

Claim 6

In combination: four transistors, each having base, collector and emitter electrodes, the first and second of said transistors connected base electrode-to-base electrode and emitter electrode-to-emitter electrode, the first and second and third of said transistors being of one conductivity type and the fourth of another conductivity type; a current sensing element connected to the collector of said first transistor for sensing the collector current of said transistor; the emitter-to-collector path of said third transistor being connected across the emitter-to-base path of said first transistor; the emitter-to-base path of said fourth transistor being connected across said current sensing element in a direction to produce emitter-to-base current flow in said fourth transistor when the current flow in said sensing element exceeds a given value; and the collector electrode of said fourth transistor connected to the base of said third transistor for delivering the collector current of said fourth transistor to the base-emitter path of said third transistor.

Claim 7

In the combination as set forth in claim 4, said first transistor having an effective emitter-base junction area which is substantially larger than that of said second transistor.

Claim 8

Composite transistor device with over-current protection comprising: a first and a second and a third terminals, corresponding respectively to the ''''emitter''''base'''' and ''''collector'''' electrodes of said composite transistor device; a first and a second and a third transistors, each having a base and an emitter and a collector electrodes, said first and said third transistors being of a conductivity type complementary to that of said second transistor and having their emitter electrodes connected to said first terminal, said third transistor collector electrode being connected to said first transistor base electrode which is connected to said second terminal, said second transistor collector electrode being coupled to said third transistor base electrode, said second transistor emitter electrode being connected to said third terminal; a resistance connected between said third terminal and an interconnection of said first transistor collector electrode and said second transistor base electrode; and at least one further transistor of the same conductivity type as said first transistor having an emitter electrode connected to said first terminal, having a base electrode connected to said second terminal, and having a collector electrode connected to said third terminal.

Claim 9

Composite transistor device with over-current protection comprising: a first and a second and a third terminals, corresponding respectively to the ''''emitter''''base'''' and ''''collector'''' electrodes of said composite transistor device; a first and a second and a third transistors, each having a base and an emitter and a collector electrodes, said first and said third transistors being of a conductivity type complementary to that of said second transistor and having their emitter electrodes connected to said first terminal, said third transistor collector electrode being connected to said first transistor base electrode which is connected to said second terminal, said second transistor collector electrode being coupled to said third transistor base electrode, said second transistor emitter electrode being connected to said third terminal; a resistance connected between said third terminal and an interconnection of said first transistor collector electrode and said second transistor base electrode; and at least one further transistor of the same conductivity type as said first transistor having an emitter electrode connected to said first terminal, having a base electrode connected to said second terminal, and having a collector electrode connected to said third terminal.

Claim 10

Composite transistor device with over-current protection comprising: a first and a second and a third terminals, corresponding respectively to the ''''emitter'''', ''''base'''' and ''''collector'''' electrodes of said composite transistor device; a first and a second transistors of the same conductivity type, each having a base and an emitter and a collector electrodes, having their emitter electrodes connected to said first terminal, said second transistor collector electrode being connected to said first transistor base electrode which is connected to said second terminal; a resistive element connecting said second transistor Base electrode to said first terminal; and a third and a fourth transistors of a conductivity type opposite to that of said first and said second transistor, said third and said fourth transistors each having an emitter electrode connected to said third terminal, said third and said fourth transistors each having a collector electrode, said third transistor collector electrode being connected to said first transistor collector electrode, said fourth transistor collector electrode being connected to said second transistor base electrode, said third and said fourth transistors each having a base electrode connected to said third transistor collector electrode.

Claim 11

Composite transistor device with over-current protection comprising: a first and a second and a third terminals, corresponding respectively to the ''''emitter'''', ''''base'''' and ''''collector'''' electrodes of said composite transistor device; a first and a second transistors of the same conductivity type, each having a base and an emitter and a collector electrodes, having their emitter electrodes connected to said first terminal, said second transistor collector electrode being connected to said first transistor base electrode which is connected to said second terminal; a resistive element connecting said second transistor Base electrode to said first terminal; and a third and a fourth transistors of a conductivity type opposite to that of said first and said second transistor, said third and said fourth transistors each having an emitter electrode connected to said third terminal, said third and said fourth transistors each having a collector electrode, said third transistor collector electrode being connected to said first transistor collector electrode, said fourth transistor collector electrode being connected to said second transistor base electrode, said third and said fourth transistors each having a base electrode connected to said third transistor collector electrode.