Amplifier overload protection circuit

Claim 2

An amplifier overload protection circuit comprising: A. a first amplifier having inverting and noninverting inputs and an output; B. circuit load means, wherein said circuit load means comprises variable impedance means whose impedance value remains above a specified value until a predetermined voltage appears across said variable impedance means and which variable impedance means lowers in impedance value once said predetermined voltage is exceeded, and wherein said variable impedance means includes a first plurality of diodes connected in series and a second plurality of diodes connected in series, said first and second plurality of diodes connected in parallel, said first plurality of diodes connected in a first easy current flow direction and said second plurality of diodes connected in a second easy current flow direction opposite that of said first plurality of diodes; C. current-limiting means coupled between said amplifier output and said circuit load means for increasingly limiting current drawn by said circuit load means from said amplifier output as said current exceeds a predetermined value; D. coupling means for coupling the junction of said currentlimiting means and said circuit load means to said inverting input; and E. feedback means connected between said amplifier output and said inverting input for decreasing impedance between said output and said inverting input as said current exceeds said predetermined value, whereby the coupling to said inverting input changes from said junction to said output as said current exceeds said predetermined value.

Claim 3

An amplifier overload protection circuit comprising: A. a first amplifier having inverting and noninverting inputs and an output; B. circuit load means; C. current-limiting means coupled between said amplifier output and said circuit load means for increasingly limiting current drawn by said circuit load means from said amplifier output as said current exceeds a predetermined value, said current-limiting means comprising a diode bridge comprising four diodes so arranged that each of said diodes is forward biased when said current is less than said predetermined value and so that opposite, noncontiguous diodes become increasingly reverse biased as said current exceeds said predetermined value; D. coupling means for coupling the junction of said current limiting means and said circuit load means to said inverting input; and E. feedback means connected between said amplifier output and said inverting input for decreasing impedance between said output and said inverting input As said current exceeds said predetermined value, whereby the coupling to said inverting input changes from said junction to said output as said current exceeds said predetermined value.

Claim 4

An amplifier overload protection circuit comprising: A. a first amplifier having inverting and noninverting inputs and an output; B. circuit load means; C. current-limiting means coupled between said amplifier output and said circuit load means for increasingly limiting current drawn by said circuit load means from said amplifier output as said current exceeds a predetermined value, said current-limiting means comprising a diode bridge comprising four diodes so arranged that each of said diodes is forward biased when said current is less than said predetermined value and so that opposite, noncontiguous diodes become increasingly reverse biased as said current exceeds said predetermined value; D. coupling means for coupling the junction of said current limiting means and said circuit load means to said inverting input; and E. feedback means connected between said amplifier output and said inverting input for decreasing impedance between said output and said inverting input As said current exceeds said predetermined value, whereby the coupling to said inverting input changes from said junction to said output as said current exceeds said predetermined value.

Claim 5

A circuit as defined in claim 2 wherein said feedback means includes at least one diode connected between said output and said second input so that said diode is forward biased when said current is greater than said predetermined value and so that said diode provides a high impedance when said current is less than said predetermined value.

Claim 6

A circuit as defined in claim 3 wherein said amplifier is an operational amplifier, said operational amplifier having a feedback path to said inverting input regardless of the value of said current.

Claim 7

A circuit as defined in claim 2 wherein said feedback means includes at least one transistor having a base, a collector, and an emitter, said base coupled to said junction of said current-limiting means and said circuit load means, said collector coupled to said second input and said emitter connected to said output.

Claim 8

A circuit as defined in claim 5 further including a diode connected between said collector and said second input.

Claim 9

A circuit as defined in claim 6 further including an impedance coupled between said junction and said base.

Claim 10

A circuit as defined in claim 5 wherein said amplifier is an operational amplifier and further including: A. switch means; and B. impedance means, said switch means and impedance means coupled together and with said operational amplifier to provide said operational amplifier with a programmable voltage gain depending on the gain selection by said switch means.

Claim 11

An amplifier overload protection circuit comprising: A. a first amplifier having inverting and noninverting inputs and an output; B. circuit load means; C. current-limiting means coupled between said amplifier output and said circuit load means for increasingly limiting current drawn by said circuit load means from said amplifier output as said current exceeds a predetermined value; D. coupling means for coupling the junction of said current-limiting means and said circuit load means to said inverting input; E. feedback means connected between said amplifier output and said inverting input for decreasing impedance between said output and said inverting input as said current exceeds said predetermined value, whereby the coupling to said inverting input changes from said junction to said output as said current exceeds said predetermined value; F. a second amplifier similar to said first amplifier; G. a second means for limiting, similar to said first means for limiting; H. a second feedback means, similar to said first feedback means; I. a second coupling means for coupling, similar to said first means for coupling; J. wherein said noninverting input of said first and second amplifiers provide a differential input; and K. wherein said circuit load means includes a semiconductor circuit coupled to receive current from both said first and second current-limiting means, said semiconductor circuit providing a high impedance when the differential value between said currents is below said predetermined value, and said semiconductor circuit providing a low impedance when said differential value is above said predetermined value.

Claim 12

An amplifier overload protection circuit comprising: A. a first amplifier having inverting and noninverting inputs and an output; B. circuit load means; C. current-limiting means coupled between said amplifier output and said circuit load means for increasingly limiting current drawn by said circuit load means from said amplifier output as said current exceeds a predetermined value; D. coupling means for coupling the junction of said current-limiting means and said circuit load means to said inverting input; E. feedback means connected between said amplifier output and said inverting input for decreasing impedance between said output and said inverting input as said current exceeds said predetermined value, whereby the coupling to said inverting input changes from said junction to said output as said current exceeds said predetermined value; F. a second amplifier similar to said first amplifier; G. a second means for limiting, similar to said first means for limiting; H. a second feedback means, similar to said first feedback means; I. a second coupling means for coupling, similar to said first means for coupling; J. wherein said noninverting input of said first and second amplifiers provide a differential input; and K. wherein said circuit load means includes a semiconductor circuit coupled to receive current from both said first and second current-limiting means, said semiconductor circuit providing a high impedance when the differential value between said currents is below said predetermined value, and said semiconductor circuit providing a low impedance when said differential value is above said predetermined value.

Claim 13

A circuit as defined in claim 9 wherein said semiconductor circuit includes first and second zener diodes each having an anode and a cathode, said anodes connected together and each said cathodes coupled to one of said current limiting means.

Claim 14

A circuit as defined in claim 9 wherein said diode circuit includes at least a first diode connected in parallel with at least a second diode, said diodes having anodes and cathodes, wherein the cathode of said first diode is connected to the anode of said second diode and to one of said current-limiting means, the other ends of said diodes connected together and to the other of said current-limiting means.

Claim 15

An amplifier overload protection circuit comprising: A. an amplifier having inverting and noninverting inputs and an output, said noninverting input coupled to receive a signal; B. an output circuit having an input; C. current-limiting means coupled between said output and said input of said output circuit, said current-limiting means comprising a diode bridge so arranged that each of said diodes is forward biased when current from said amplifier output is below a predetermined value thereby providing a low-impedance path from said output to said output circuit input; D. coupling means for coupling said output circuit input to said inverting input; E. a semiconductor circuit coupled between said output and said inverting input, said semiconductor circuit providing a high impedance path when said current is below said predetermined value; and F. wherein as said output circuit begins to draw an overload current from said amplifier, said diode bridge provides a high impedance path and said semiconductor circuit provides a low-impedance path so that the feedback coupling to said inverting input changes from said output circuit input to said amplifier output.

Claim 16

An amplifier overload protection circuit comprising: A. an amplifier having inverting and noninverting inputs and an output, said noninverting input coupled to receive a signal; B. an output circuit having an input; C. current-limiting means coupled between said output and said input of said output circuit, said current-limiting means comprising a diode bridge so arranged that each of said diodes is forward biased when current from said amplifier output is below a predetermined value thereby providing a low-impedance path from said output to said output circuit input; D. coupling means for coupling said output circuit input to said inverting input; E. a semiconductor circuit coupled between said output and said inverting input, said semiconductor circuit providing a high impedance path when said current is below said predetermined value; and F. wherein as said output circuit begins to draw an overload current from said amplifier, said diode bridge provides a high impedance path and said semiconductor circuit provides a low-impedance path so that the feedback coupling to said inverting input changes from said output circuit input to said amplifier output.

Claim 17

A circuit as defined in claim 12 wherein said semiconductor circuit includes first and second diodes connected between said output and said inverting input so that said first diode is forward biased when said current is a first polarity and is greater than said predetermined value and so that said second diode is forward biased where said signal is a second polarity and is greater than said predetermined value and so that both of said diodes provide a high impedance when said current is less than said predetermined value.

Claim 18

A circuit as defined in claim 12 wherein said semiconductor circuit includes first and second complementary transistors, each of said transistors having a base, an emitter, and a collector, said bases coupled to said output circuit input, said emitters coupled to said output, and said collectors coupled to said inverting input so that the emitter-collector path of one of said transistors is forward biased when said current is greater than said predetermined value.

Claim 19

A circuit as defined in claim 14 further including first and second diodes connected in the easy current flow direction from said collectors of said first and second transistors respectively, to said inverting input.

Claim 20

A circuit as defined in claim 14 further including means for selecting the voltage gain of said amplifier, said means for selecting comprising: A. a plurality of switch means; B. first and second impedance networks arranged between said output circuit input, a first potential and by way of said plurality of switch means to said inverting input so as to result in a voltage amplifier configuration; and C. wherein a voltage gain is selected by activation of one of said plurality of switch means.

Claim 21

A circuit as defined in claim 12 wherein said means for coupling includes an impedance means.