Amplifier protection circuit

Claim 2

A protection circuit for an electrical signal amplifier comprising in combination first and second opposite conductivity transistors each having a base, emitter, and collector electrodes; a signal input circuit; means coupling said signal input circuit to the base electrodes of said transistors including common signal coupling means connected between the base electrodes of said transistors; an output circuit; means coupling said emitters to said output circuit including a current sampling impedance in the current path of at least one of said emitters; electronic switch means coupled between said common signal coupling means and said output circuit to form a circuit loop including said emitter, said current sampling impedance and said electronic switch means, said switch means being responsive to voltage developed across said current sampling impedance to provide a low impedance path between said common signal coupling means and said output circuit when said voltage exceeds a threshold value.

Claim 3

A protection circuit as defined in claim 1 wherein the current sampling impedance is a resistor.

Claim 4

A protection circuit as defined in claim 1 wherein said electronic switch means is a diode which provides said low impedance path when a threshold voltage is exceeded for at least one polarity of applied voltage.

Claim 5

A protection circuit as defined in claim 3 wherein said signal input circuit includes a driver transistor having a collector electrode connected in common to the base electrodes of said first and second transistors, and being of the same conductivity type as said second transistor, and wherein said diode is poled to be driven toward forward current conduction by current flow between the emitter and collector electrodes of said first transistor.

Claim 6

A protection circuit as defined in claim 4 wherein said diode comprises a Zener diode.

Claim 7

A protection circuit as defined in claim 2 including a third and fourth transIstor of the same conductivity type as said second transistor; means connecting the emitter electrode of said second transistor to the base electrode of said third transistor; means connecting the collector electrode of said first transistor to the base electrode of said fourth transistor; said resistor being in series with the collector-to-emitter current path of one of said third and fourth transistors.

Claim 8

A protection circuit as defined in claim 6 including a second current sampling impedance means which comprises a second resistor in series with the other of said third and fourth transistor emitter collector current paths and said electronic switch means is a bidirectionally conductive device conducting current when a threshold voltage is exceeded for each polarity of applied voltage.

Claim 9

A transistor amplifier circuit including first and second opposite conductivity transistors each having base, emitter and collector electrodes; a driver transistor having base, emitter and collector electrodes and being of the same conductivity type as said second transistor; signal input circuit coupled between the base and emitter electrodes of said driver transistor; means connecting the collector electrode of said driver transistor to the base electrode of said first transistor; a common impedance element connected between the base electrodes of said first and second transistors; a pair of output terminals; means including at least one resistor connecting one of said output terminals to the emitter electrode of one of said first and second transistors and a diode connected between said one of said output terminals and the common impedance element, said diode being poled in a direction such that current from said first transistor through said resistor tends to forward bias said diode.

Claim 10

A transistor amplifier circuit including first and second opposite conductivity transistors each having base, emitter and collector electrodes; a driver transistor having base, emitter and collector electrodes and being of the same conductivity type as said second transistor; signal input circuit coupled between the base and emitter electrodes of said driver transistor; means connecting the collector electrode of said driver transistor to the base electrode of said first transistor; a common impedance element connected between the base electrodes of said first and second transistors; a pair of output terminals; means including at least one resistor connecting one of said output terminals to the emitter electrode of one of said first and second transistors and a diode connected between said one of said output terminals and the common impedance element, said diode being poled in a direction such that current from said first transistor through said resistor tends to forward bias said diode.

Claim 11

An amplifier circuit comprising: a driver transistor of a first conductivity type having base, emitter and collector electrodes; a signal input circuit coupled between the base and emitter electrodes of said driver transistor; first, second and third transistors each having base, emitter and collector electrodes and being of the same conductivity type as the driver transistor, a fourth transistor having base, emitter and collector electrodes and being of a conductivity type opposite of that of said driver transistor; means connecting the collector electrode of said driver transistor to the base electrode of said fourth transistor; a resistive means and first, second and third rectifier devices connected in the order named between the base electrode of said first transistor and base electrode of said fourth transistor; means connecting the emitter electrode of said first transistor to the base electrode of said second transistor; means connecting the collector electrode of the fourth transistor to the base electrode of the third transistor; a pair of output terminals; a fourth rectifier device and second resistive means connected between the emitter electrode of the second transitor and one of said output terminals; third resistive means connected between the collector electrode of the third transistor and said one of said pair of output terminals; a diode connected between said one of said output terminals and the junction of said first and second rectifier devices; said diode being poled in a direction such that an increase in the voltage drop across said third resistive element tends to bias said diode in a forward direction.

Claim 12

An amplifier circuit comprising: a driver transistor of a first conductivity type having base, emitter and collector electrodes; a signal input circuit coupled between the base and emitter electrodes of said driver transistor; first, second and third transistors each having base, emitter and collector electrodes and being of the same conductivity type as the driver transistor, a fourth transistor having base, emitter and collector electrodes and being of a conductivity type opposite of that of said driver transistor; means connecting the collector electrode of said driver transistor to the base electrode of said fourth transistor; a resistive means and first, second and third rectifier devices connected in the order named between the base electrode of said first transistor and base electrode of said fourth transistor; means connecting the emitter electrode of said first transistor to the base electrode of said second transistor; means connecting the collector electrode of the fourth transistor to the base electrode of the third transistor; a pair of output terminals; a fourth rectifier device and second resistive means connected between the emitter electrode of the second transitor and one of said output terminals; third resistive means connected between the collector electrode of the third transistor and said one of said pair of output terminals; a diode connected between said one of said output terminals and the junction of said first and second rectifier devices; said diode being poled in a direction such that an increase in the voltage drop across said third resistive element tends to bias said diode in a forward direction.