Transistorized amplifiers and protective circuits therefor

Claim 2

A protective network for a transistor amplifier circuit having a pair of transistors with series-connected output circuits and with input circuits driven by respective outputs of complementary phase inverter transistors to which the amplifier input signal is applied, said network comprising a negative feedback path between the junction of said series-connected output circuits and at least one of said phase inverter transistors; switching means capable of being biased to either a conductive or a nonconductive state in said feedback path, means normally biasing said switching means to a conductive state, and biasing said switching means to a nonconductive state when the current through said feedback path reaches a predetermined level indicative of excessive transistor current; further switching means capable of being biased to either a conductive or a nonconductive state; said further switching means connecting said junction to the signal input terminal of said amplifier circuit; said further switching means normally biased to a nonconductive state by the normally conductive condition of the first-named switching means, and biased to a conductive state in response to the assumption by said first-named switching means of a nonconductive state for driving said amplifier circuit into a cutoff condition.

Claim 3

The combination according to claim 1 wherein said first-named and further switching means are diodes.

Claim 4

A transistorized power amplifier for audio input signal, comprising a first transistor amplifier stage for providing high voltage gain, feedback means for DC stabilization of said first stage; a second transistor amplifier stage fOr providing an impedance buffer and a power gain, said second stage including a pair of complementary symmetry transistors responsive to audio output signal from said first amplifier stage applied to a common input junction of said pair for developing balanced oppositely phased signals and a further pair of transistors having series-connected output circuits and having input circuits responsive respectively to said oppositely phased signals to provide the audio output signal of the overall amplifier; feedback means for DC stabilization of said second stage; and means AC coupling the high gain output of said first stage to said common input junction of said complementary symmetry transistors; said second stage including means for cutting off the last-named audio output signal by reduction of transistor currents in said second stage in response to said transistor currents exceeding a predetermined acceptable level.

Claim 5

A transistorized power amplifier for audio input signal, comprising a first transistor amplifier stage for providing high voltage gain, feedback means for DC stabilization of said first stage; a second transistor amplifier stage fOr providing an impedance buffer and a power gain, said second stage including a pair of complementary symmetry transistors responsive to audio output signal from said first amplifier stage applied to a common input junction of said pair for developing balanced oppositely phased signals and a further pair of transistors having series-connected output circuits and having input circuits responsive respectively to said oppositely phased signals to provide the audio output signal of the overall amplifier; feedback means for DC stabilization of said second stage; and means AC coupling the high gain output of said first stage to said common input junction of said complementary symmetry transistors; said second stage including means for cutting off the last-named audio output signal by reduction of transistor currents in said second stage in response to said transistor currents exceeding a predetermined acceptable level.

Claim 6

A transistorized power amplifier, comprising a first stage of cascaded transistors for providing high signal gain, feedback means for DC stabilization of said first stage; a second stage including a pair of complementary transistors connected to supply balanced oppositely phased signals in response to application of signal to a common input junction thereof, and a further pair of transistors having series-connected output circuits and having input circuits responsive respectively to said oppositely phased signals to provide the output signal of said amplifier, feedback means for DC stabilization of said second stage; and means AC coupling the high gain output of said first stage to said common input junction of said complementary transistors; said second stage including means for cutting off signal therethrough in response to the transistor currents therein exceeding a predetermined acceptable level, the last-named means including normally conductive switching means supplying a negative feedback path from one of said further pair of transistors to one of said complementary transistors, and normally nonconductive switching means, responsive to the breaking of said negative feedback path by the energization of said normally conductive switching means to a nonconductive state in the presence of said transistor currents exceeding said level, for supplying a conductive path between the output junction of said series-connected output circuits and said common input junction.

Claim 7

A transistorized power amplifier, comprising a first stage of cascaded transistors for providing high signal gain, feedback means for DC stabilization of said first stage; a second stage including a pair of complementary transistors connected to supply balanced oppositely phased signals in response to application of signal to a common input junction thereof, and a further pair of transistors having series-connected output circuits and having input circuits responsive respectively to said oppositely phased signals to provide the output signal of said amplifier, feedback means for DC stabilization of said second stage; and means AC coupling the high gain output of said first stage to said common input junction of said complementary transistors; said second stage including means for cutting off signal therethrough in response to the transistor currents therein exceeding a predetermined acceptable level, the last-named means including normally conductive switching means supplying a negative feedback path from one of said further pair of transistors to one of said complementary transistors, and normally nonconductive switching means, responsive to the breaking of said negative feedback path by the energization of said normally conductive switching means to a nonconductive state in the presence of said transistor currents exceeding said level, for supplying a conductive path between the output junction of said series-connected output circuits and said common input junction.

Claim 8

The combination according to claim 4 wherein said switching means are diodes.

Claim 9

A transistor amplifier for amplification and power transfer of audio signal from a source thereof to a load, said amplifier comprising a high input impedance complementary-symmetry phase inverter including a pair of transistors of opposite conductivity types concurrently responsive to audio signal applied in parallel thereto for developing balanced oppositely phased signals representative of the applied audio signal, an output stage including a further pair of transistors having their output circuits coupled at a common output junction to provide a low output impedance and having input circuits respectively responsive to said oppositely phased signals for producing at said output junction an audio output signal constituting a substantial replica of said applied audio signal, a negative feedback network from said further pair of transistors to said phase inverter for DC stabilization of that portion of said amplifier including said phase inverter and said output stage, means in said feedback network responsive to overdriving of said portion of said amplifier to open said feedback network, and means coupled to said feedback network and to said phase inverter and responsive to the opening of said feedback network for cutting off audio signal through said portion of said amplifier.

Claim 10

A transistor amplifier for amplification and power transfer of audio signal from a source thereof to a load, said amplifier comprising a high input impedance complementary-symmetry phase inverter including a pair of transistors of opposite conductivity types concurrently responsive to audio signal applied in parallel thereto for developing balanced oppositely phased signals representative of the applied audio signal, an output stage including a further pair of transistors having their output circuits coupled at a common output junction to provide a low output impedance and having input circuits respectively responsive to said oppositely phased signals for producing at said output junction an audio output signal constituting a substantial replica of said applied audio signal, a negative feedback network from said further pair of transistors to said phase inverter for DC stabilization of that portion of said amplifier including said phase inverter and said output stage, means in said feedback network responsive to overdriving of said portion of said amplifier to open said feedback network, and means coupled to said feedback network and to said phase inverter and responsive to the opening of said feedback network for cutting off audio signal through said portion of said amplifier.

Claim 11

The amplifier according to claim 6 wherein said feedback network comprises an electrical connection from said common output junction of said output staGe to the output circuits of said phase inverter transistors, and wherein said means for opening said feedback network includes at least one normally forward biased semiconductor diode in said electrical connection.

Claim 12

The amplifier according to claim 7 wherein said means for cutting off audio signal includes a normally reverse biased semiconductor diode connected between said output junction and the input circuits of said phase inverter transistors and responsive to said opening of said feedback network to switch to a forward biased state in the direction of said input circuits.

Claim 13

A protective circuit for a transistor amplifier, said amplifier comprising a driver stage including a pair of series-connected transistors in class B configuration having a common signal input point and responsive to audio signal applied thereto to produce a pair of balanced oppositely phased output signals, an output stage including a pair of series-connected class B transistors having an output load point at the junction therebetween and responsive respectively to said oppositely phased signals to produce a substantial replica of said audio input signal at a load connected to said output point, said amplifier having substantially unity voltage gain and effecting a transition between a high impedance source of said audio signal and a low impedance load, and a feedback path from said output load point to said driver stage to correct DC level shifts relative to a DC reference level at said signal input point; said protective circuit comprising first electronic switch means in said feedback path, means normally rendering said first switch means conductive to close said feedback path, and responsive to overdriving of said amplifier to render said first switch means nonconductive, whereby to open said feedback path and prevent destructive current multiplication therethrough as a result of said level shift correction, and second electronic switch means connecting said output load point to said signal input point, and responsive to said feedback path being in a closed condition to assume an open state, and responsive to said feedback path being in an open condition to assume a closed state, whereby to prevent signal passage through said amplifier in the event of overdrive of said amplifier.

Claim 14

A protective circuit for a transistor amplifier, said amplifier comprising a driver stage including a pair of series-connected transistors in class B configuration having a common signal input point and responsive to audio signal applied thereto to produce a pair of balanced oppositely phased output signals, an output stage including a pair of series-connected class B transistors having an output load point at the junction therebetween and responsive respectively to said oppositely phased signals to produce a substantial replica of said audio input signal at a load connected to said output point, said amplifier having substantially unity voltage gain and effecting a transition between a high impedance source of said audio signal and a low impedance load, and a feedback path from said output load point to said driver stage to correct DC level shifts relative to a DC reference level at said signal input point; said protective circuit comprising first electronic switch means in said feedback path, means normally rendering said first switch means conductive to close said feedback path, and responsive to overdriving of said amplifier to render said first switch means nonconductive, whereby to open said feedback path and prevent destructive current multiplication therethrough as a result of said level shift correction, and second electronic switch means connecting said output load point to said signal input point, and responsive to said feedback path being in a closed condition to assume an open state, and responsive to said feedback path being in an open condition to assume a closed state, whereby to prevent signal passage through said amplifier in the event of overdrive of said amplifier.