Protection circuit for an output transistor

Claim 2

A protection circuit-for an output transistor - having a base electrode, an emitter electrode, and a collector electrode, the protection circuit comprising; first circuit means connected between the collector electrode and emitter electrode of the transistor, for producing a first voltage dependent upon the collector current of said output transistor; second circuit means connected in parallel to said first means for producing a second voltage dependent upon the collector to emitter voltage of said output transistor; and third circuit means coupled to said first and second means for combining said first and second voltages and for producing a protection signal in accordance with the combination of the said signals.

Claim 3

A protection circuit according to claim 1, wherein said first means comprises; a first transistor having a base electrode connected to the base electrode of said output transistor, an emitter electrode coupled to said second terminal, and a collector electrode coupled to said first terminal.

Claim 4

A protection circuit according to claim 2, wherein said first means further comprises; a first semiconductor device having a first PN junction coupled between the collector electrode of said first transistor and said first terminal.

Claim 5

A protection circuit according to claim 3, wherein said second means comprises; a resistor and a second semiconductor device having a second PN junction.

Claim 6

A protection circuit according to. claim 4, wherein said third means connects said first and second PN junctions serially between said first and second terminals.

Claim 7

A protection circuit for and according to claim 5, in which the third means includes fourth circuit means for producing the said protection signal and comprising; a third transistor having a base electrode being supplied with said combined voltage of said first and second voltages, and an emitter electrode coupled to said first terminal means, and thereby produces said protecting signal from a collector electrode thereof.

Claim 8

A protection circuit according to claim 6, wherein said fourth means further comprises; a third semiconductor device having a third PN junction between the emitter electrode of said third transistor and said first terminal.

Claim 9

A protection circuit according to claim 8, further comprising; a constant current, source having an output terminal coupled to the emitter electorde of said third transistor.

Claim 10

A protection circuit according to claim 1, wherein said output transistor is an output transistor in a complementary class B push-pull amplifier.

Claim 11

A protection circuit for an output transistor having a base electrode, an emitter electrode, and a collector electrode, comprising; a first terminal coupled to the collector electrode of said output transistor; a second terminal coupled to the emitter electrode of said output terminal; a first transistor haviang a base electrode, an emitter electrode and a collector electrode; first means for connecting the base electrode' of said first transistor to the base electrode of said output transistor; first resistor means coupled-between said emitter electrode and said second terminal; second means comprising first diode means and second resistor means for connecting said collector electrode of said first transistor to said first terminal; a second transistor having a base electrode, an emitter electrode and a collector electrode;. second means for connecting the base electrode of said second transistor to the collector electrode of said first transistor; third means for connecting the collector electrode of said second transistor to said first terminal; third resistor means coupled between said emitter electrode of said second transistor and said second terminal; a fourth transistor having a base electrode, an emitter electrode and a collector electrode; fourth means for connecting the base electorde of said fourth transistor to the emitter electrode of said third transistor; and second diode means coupled between said emitter electrode of said third transistor and said first terminal, thereby producing a protecting signal from the collector electrode of said third transistor.

Claim 12

A protection circuit for an output transistor having a base electrode, an emitter electrode, and a collector electrode, comprising; a first terminal coupled to the collector electrode of said output transistor; a second terminal coupled to the emitter electrode of said output terminal; a first transistor haviang a base electrode, an emitter electrode and a collector electrode; first means for connecting the base electrode' of said first transistor to the base electrode of said output transistor; first resistor means coupled-between said emitter electrode and said second terminal; second means comprising first diode means and second resistor means for connecting said collector electrode of said first transistor to said first terminal; a second transistor having a base electrode, an emitter electrode and a collector electrode;. second means for connecting the base electrode of said second transistor to the collector electrode of said first transistor; third means for connecting the collector electrode of said second transistor to said first terminal; third resistor means coupled between said emitter electrode of said second transistor and said second terminal; a fourth transistor having a base electrode, an emitter electrode and a collector electrode; fourth means for connecting the base electorde of said fourth transistor to the emitter electrode of said third transistor; and second diode means coupled between said emitter electrode of said third transistor and said first terminal, thereby producing a protecting signal from the collector electrode of said third transistor.

Claim 13

A protection circuit for an output transistor having a base electrode, an emitter electrode and a collector electrode, comprising; a first terminal coupled to the collector - electrode of said output transistor; a second terminal coupled to the emitter electrode of said output transistor; a first transtor having a base electrode, an emitter electrode and a collector electrode; first means for connecting the base electrode of said first transistor to the base electrode of said output transistor; first resistor means coupled between said emitter electrode of said first transistor and said second terminal; a second transistor having a base electrode, an emitter electrode and a collector electrode; second resistor means coupled between said collector electrode of said first transistor and the emitter electrode of said second transistor; second means for connecting the collector electrode of said second transistor to said first terminal; first diode means coupled between said base electrode of said second transistor and said first terminal; third resistor means coupled between said first diode means and said second terminal; a third transistor having a base electrode, an emitter electrode and a collector electrode; third means for connecting the base electrode of said third transistor to the collector electrode of said first transistor; and second diode means coupled between the emitter electrode of said third transistor and said first terminal means, thereby producing a protecting signal from the collector electrode of said third transistor.

Claim 14

A protection circuit for an output transistor having a base electrode, an emitter electrode and a collector electrode, comprising; a first terminal coupled to the collector - electrode of said output transistor; a second terminal coupled to the emitter electrode of said output transistor; a first transtor having a base electrode, an emitter electrode and a collector electrode; first means for connecting the base electrode of said first transistor to the base electrode of said output transistor; first resistor means coupled between said emitter electrode of said first transistor and said second terminal; a second transistor having a base electrode, an emitter electrode and a collector electrode; second resistor means coupled between said collector electrode of said first transistor and the emitter electrode of said second transistor; second means for connecting the collector electrode of said second transistor to said first terminal; first diode means coupled between said base electrode of said second transistor and said first terminal; third resistor means coupled between said first diode means and said second terminal; a third transistor having a base electrode, an emitter electrode and a collector electrode; third means for connecting the base electrode of said third transistor to the collector electrode of said first transistor; and second diode means coupled between the emitter electrode of said third transistor and said first terminal means, thereby producing a protecting signal from the collector electrode of said third transistor.