Abstract: The disclosed protection circuit which is suitable for providing protection of transistors included in integrated circuits such as regulators and power amplifiers, includes thermal shutdown, safe area and current control circuits. The current control portion includes a sense transistor connected substantially in parallel with the transistor to be protected. In monolithic integrated circuit applications, the sense transistor has an emitter area that is a predetermined ratio of the emitter area of the protected transistor. A "sense resistor" is connected to the sense transistor and develops a control signal which is proportional to the instantaneous current being conducted by the protected transistor. A threshold circuit is coupled between the sense resistor and the drive circuit for the protected transistor and responds to the magnitude of the control signal crossing a predetermined threshold to remove or reduce the drive to the protected transistor.

Abstract: An electronic ignition control device for an internal combustion engine includes a power amplifier which controls current through an ignition coil and a triggering circuit for the power amplifier. To protect the power amplifier against damage resulting from being connected to a higher voltage source during starting there is a protection circuit which switches off the power amplifier when an over voltage is detected but allows it to switch on for a very short period when a spark is required. The protection circuit uses conventional logic elements, sensing the output of the triggering means, the output of a delay circuit driven by the triggering means, and the output of an over voltage sensing circuit.

Abstract: A directional power detector mounted between the power amplifier and antenna which supplies audio frequency output signals indicative of forward and reflected power, circuitry for summing and converting the output signals from the power detector means to a DC potential proportional to the magnitude thereof and a transistor connected in shunt at the input of the power amplifier and controlled by the DC potential for controlling the peak envelope power at the antenna.

Abstract: An overload protection circuit for an amplifier is disclosed in which a signal supply means connected with the input of the amplifier is deactivated when the output of the amplifier exceeds a given value. Transducer means of the optoelectrical type are connected with the output terminals of the amplifier for operating a bistable device such as an operational amplifier to deactivate the signal supply means as long as the overload voltage occurs. Timing capacitor means maintain the signal supply means de-activated for a given period of time after the overload condition is terminated.

Abstract: A load protective circuit having a class B amplifying stage driven by a class A amplifier and a load DC coupled to the class B stage, in which means are provided for detecting an undesirable DC voltage at the output of the class B amplifying stage and for producing a control signal in response to the output of the detecting means. A first protective means shunts the input signal to the class B amplifier to ground in response to the control signal. A second protective means controls a switching means connected between the output point and ground so as to connect the output point of the class B amplifier to ground in response to the control signal to thereby remove any undesirable DC voltage from the output point of the amplifier and to protect the DC coupled load from being damaged.

Abstract: An amplifier circuit including provision for detecting non-linear circuit operation caused by the application of input signals that exceed either the amplifier dynamic range or the amplifier slewing capability is disclosed. The amplifier circuit includes the cascaded combination of a voltage amplifier stage, a voltage-to-current converter stage, a current limiter stage and an output stage. A first signal, obtained at the junction between a capacitor and resistor that are series connected between the signal common or ground potential and the input terminal to the output stage, is compared with a second signal obtained at the input terminal of the voltage to current converter stage. When the amplifier circuit is operating within the linear region these two signals are of equal magnitude or exhibit some other known relationship to one another.

Abstract: One junction field effect transistor is connected in shunt with an operational amplifier so as to render its gain zero when no voltage is applied to its gate and another junction field effect transistor is connected so as to shunt the output of the amplifier to ground when no voltage is applied to its gate.

Abstract: A protective circuit effective for use with an output capacitor less type transistor amplifier includes a load impedance detecting circuit and a detecting circuit for detecting an undesirable DC voltage applied to a load. The load impedance detecting circuit comprises first and second DC bridge circuits for detecting a load impedance, and the DC voltage detecting circuit comprises third and fourth DC bridge circuits. Both the load and amplifier are protected by outputs from the first through fourth bridge circuits so as to be free from a load-shorted state and an undesirable DC voltage.

Abstract: A protective circuit for a transistor amplifier is provided which measures the load impedance and actuates a protective means across an input terminal of the transistor amplifier when a measured value of said load impedance becomes lower than a predetermined value, to protect the transistor amplifier from overload. The protective circuit is applicable for a class B push-pull amplifier and, particularly effective to protect the overload even when the load of the amplifier has a reactance component. Various modifications such as relay type protective circuits are also disclosed.

Abstract: An improved circuit is provided for a known amplifier having complementary input transistors in its power output stages for supplying oppositely phased signals in response to an input signal. Output transistors are connected to the input transistors to provide output signals for the amplifier. Normally conducting switching means are connected between one of the output transistors and one of the input transistors. Normally nonconducting switching means are coupled between the one output transistor and the amplifier input. During an overload or overdrive condition, the normally conducting switching means become nonconducting, and this in turn causes the normally nonconducting switching means to become conducting, and thereby limit the output from the amplifier.

Abstract: A DC linear power amplifier is disclosed having a first amplifier referenced to +14VDC, for receiving a control signal. The first amplifier in turn controls a first power stage connected to a load through a first sensing resistor. The first resistor provides a differential voltage to a second amplifier forming a current control loop with the first amplifier. A third amplifier controls a second power stage connected to the load through a second sensing resistor, so that the first and second power stages each dissipate equal power. The resistors each provide differential signals to a comparator which provides a first output signal if the current through each resistor is the same. If the differential signals are different, resulting from the load shorting to ground, the comparator provides a second output signal which turns the entire power amplifier essentially off. The entire power amplifier returns to normal when the short is eliminated.

Abstract: An electronic cut out for a circuit to be protected comprises a measuring resistor connected across the d.c. load voltage of the circuit, a differential amplifier also connected across the measuring resistor and a switch stage connected thereafter controlling a current source drive a response to the switch stage to feed current to the circuit to be protected to disconnect it.

Abstract: An electronic cut out for the protection of output stage transistors of a low frequency amplifier comprises means for producing first and second direct voltages proportional to the output alternating voltage and the collector alternating current of the output stage transistors respectively, means for comparing these voltages and igniting a thyristor if the second voltage exceeds a predetermined threshold, the thyristor being connected to short circuit the low frequency signal to earth prior to its arrival at the output stage transistors when the thyristor is ignited.

Abstract: In an amplifier device including a driving amplifier circuit and a push-pull output circuit, the push-pull output circuit consisting of a first amplifier portion which turns "on" when the drive current of the driving amplifier circuit decreases, and a second amplifier portion which turns "on" when the drive current increases, the improvement comprising the first protective circuit which is disposed on the input side of the first amplifier portion so as to branch an input current when the first amplifier portion falls outside its allowable operating range, and the second protective circuit which is disposed on the input side of the driving amplifier circuit so as to branch an input current when the second amplifier portion falls outside its allowable operating range, whereby even when the drive current of the driving amplifier circuit becomes large, the constituent parts of the push-pull output circuit can be reliably protected from being destroyed.

Abstract: An integrated circuit, current protection network wherein the point of operation (trip point) can be changed over a wide range of values by proportioning the areas of the junctions of semiconductor devices. A pair of transistors form a high gain differential amplifier, with the emitter electrodes of the transistors connected to the ends of a sense resistor through which current flows to the device to be protected. Diodes are connected between the base and emitter electrodes of the two transistors with the same polarities as the junctions, so that the current flow through the transistors will be in accordance with the areas of the junctions of the transistors and diodes. During construction of the integrated circuit, the areas of the junctions can be selected to provide the desired trip point for the network. A differential to single ended converter load circuit is connected to the collector electrodes of the transistors, and controls the protected device when the trip point is reached.

Abstract: An automatic level controller comprising a switching transistor connected to the output stage of an audio amplifying circuit to be turned off when the output signal of the audio amplifying circuit attains a predetermined level, a control transistor connected to the input stage of the audio amplifying circuit for bypassing to the ground a portion of the audio signal applied to the audio amplifying circuit thereby controlling the audio level, a diode adapted to be turned on in response to the turn-off of the switching transistor for supplying current from a power source to the audio level control transistor as an audio level control signal, and a time constant circut for setting the attack period and release period of control by the audio level control signal.

Abstract: A power supply has both high and low voltage power sources connected to a common output terminal. A switching circuit is connected between the high voltage source and this terminal, the switching circuit being controlled by a control circuit. The control circuit operates in response to malfunction and temperature sensors when these sensors have outputs indicative of equipment operating conditions outside of predetermined ranges for each of the sensed parameters. When the control circuit is not being actuated by an output from one of the sensors, the switching circuit is actuated to connect the high voltage output to the output terminal. In the event, however, that one of the temperature or malfunction sensors senses a condition outside of range, the control circuit is actuated, thereby deactuating the switching circuit to remove the high voltage output from the output terminal, leaving low voltage output.

Abstract: A compound transistor circuitry comprises a non-saturation type first field effect transistor and a saturation type second field effect transistor which is direct-coupled to the source circuit of said first FET. The internal dynamic resistance of the second FET functions as a negative feed-back element for the first FET. This internal dynamic resistance will greatly increase when the drain current of the second FET saturates. As a result, the compound transistor circuitry presents an output characteristic closely resembling that of the first FET within the operative range where the second FET does not saturate, whereas the circuitry presents an output characteristic that the current saturates at a level substantially equal to the saturating current of the second FET within the operative range where the second FET saturates.

Abstract: It is known in the art to place a low impedance path across the input circuit of an output amplifier when the power dissipation of the amplifier exceeds a given value. The present circuit includes, in addition, a gate controlled rectifier, the main conduction path of which is connected across the output terminals of the amplifier, and which is turned on in response to a flow of current through this low impedance path. This additional circuit protects the amplifier from voltage spikes produced, for example, by an inductive load, such as a speaker driven by the amplifier.

Abstract: A resistor senses low-level drive current is a logic circuit. When the output is shorted, excessive drive current turns on a sensor transistor, which causes drive voltage to the output stage to be clamped to ground, and to remain clamped until the fault is removed.

Abstract: A sense amplifier having three transistor stages. A balanced differential input stage with high noise immunity to capacitively coupled noise. A second threshold stage is provided with protection against an output being caused by a permanent potential on the input, false trigger protection circuitry, and protection against supply voltage and other minor variations. A differential output stage increases noise immunity of the amplifier output and protects against a short circuit in the output.

Abstract: A protective circuit for a pulse width modulated signal amplifier includes a signal input circuit, a carrier signal generator, a pulse width modulator for receiving both the output signals of the signal input circuit and the carrier signal generator and for producing a pulse width modulated signal, an amplifier for receiving the pulse width modulated signal and for amplifying it to drive a load through a low pass filter, a detecting circuit for detecting whether the pulse width modulated signal is present or not, or detecting DC voltage of undesirable duration produced at the output of the amplifier and for producing a control signal, and a protective circuit activated by the control signal for cutting off the operation of the amplifier.

Abstract: A field effect transistor amplifier comprising one or more depletion-type field effect transistors, preferably with triode characteristics, and having an operating voltage applied across its drain and source electrodes through a load, while an input signal to be amplified is applied to its gate electrode and a predetermined DC gate bias voltage is applied between the gate and source electrodes; is provided with a protective circuit for preventing damage to the field effect transistor by an excessive input signal that is, by over-drive, and which includes a source resistor connected in series with the source electrode and a constant voltage element, for example, constituted by one or more diodes, connected between the gate electrode and the side of the source resistor remote from the respective source electrode.

Abstract: PNP composite transistors connected as commonemitter amplifiers each comprise a PNP pre-amplifier transistor in direct coupled cascade with a plurality of parallelled NPN transistors. The emitter-electrode of the PNP transistor is connected to a sensing resistor in the collector path of one of these NPN transistors, causing the "base-to-emitter" potential of the composite transistor to increase if its "emitter" current exceeds a threshold current. By clamping this base-to-emitter potential if it exceeds a predetermined potential, the output current of the composite transistor is prevented from becoming excessive. This predetermined potential is controlled as a function of composite transistor temperature and supply potential to provide the required degree of over-current protection for these particular conditions.

Abstract: A power amplifier includes a plurality of generally identical amplifier elements connected in parallel between input and output transmission lines for phase coherent addition of the signal outputs of each amplifier element. Resistive elements are connected across normally phase identical points on the transmission lines. If the amplifier becomes electrically unbalanced, power is absorbed in the resistive elements, thus protecting the amplifier elements.

Abstract: A protective circuit for a loudspeaker connected to the output of an audio amplifier, in which a predetermined fraction of the voltage derived from the output of the power amplifier is peak rectified and stored in an accumulator provided with resistors for leaking charge from the accumulator at a predetermined rate. The voltage across the storage capacitor is normally maintained blocked in respect to application to a diode control circuit for by-passing input signal to the power amplifier. When the voltage across the storage capacitor attains a sufficiently high value, control signal is applied to oppositely poled diodes, to vary their back biases, and the diodes provide a controlled shunt path to ground for peaks of the signal applied to the input to the power amplifier.

Abstract: A power amplifier and loudspeaker protection circuit for a receiver having an AC potential source with a center-tap transformer shunted by a full-wave bridge rectifier and a power amplifier directly coupled to a loudspeaker connected to a potential reference level includes a thermal relay means coupling the bridge rectifier through normally closed contacts to a power amplifier stage and an impedance coupling the transformer center-tap to a potential reference level to activate the thermal relay means and disconnect the potential source in response to increased current flow in a loudspeaker.

Abstract: A system for igniting, by a spark, the main burner of a gas fired device without the use of a pilot light from, for example, 12 or 24 volts. A unique oscillator provides the spark power and voltage. The oscillator also supplies the power to open the gas valve. A capacitor momentarily opens the valve. The valve is maintained open when a flame is present at the main burner.

Abstract: In a signal receiver having a potential source and an amplifier stage connected to a loudspeaker, a loudspeaker and amplifier protection circuit includes a normally closed switch coupling the potential source to the amplifier stage and a protection circuit coupled to the output of the amplifier stage and responsive to positive or negative polarity DC potentials for activating the switch to disconnect the power supply from the amplifier stage.

Abstract: Two current-carrying paths are connected in parallel between a signal input terminal and an internal node to which are connected the gate electrodes of insulated-gate field-effect transistors to be protected. One path includes the conduction path of a first transistor of one conductivity type connected in series with a first diode poled in a direction to charge the internal node and the other path includes the conduction path of a second transistor of second conductivity type in series with a second diode poled in a direction to discharge the internal node. The control electrodes of the first and second transistors are connected to points of operating potential rendering the first transistor conductive in the source follower mode for input signals of one polarity and rendering the second transistor conductive in the source follower mode for input signals of opposite polarity.

Abstract: This invention refers to an overload protection circuit for an oscillatory circuit driving an electro-acoustic converter and more specifically concerns a circuit for automatically inhibiting the oscillatory circuit in the presence of an overload. The overload protection circuit monitors the collector-emitter voltage signal and the base-emitter voltage signal for providing an overlap signal responsive to the interval when both mentioned voltage signals are in their high condition. Such a condition is indicative of the power dissipated in a switching transistor of the oscillatory circuit. The overlap signal is integrated and the integrated signal is compared to a predetermined voltage level. When the integrated signal exceeds the predetermined voltage level, the oscillatory circuit is inhibited.

Abstract: A pair of Zener diodes having like electrodes interconnected for voltage suppressor functions also has a connection to their common point for obtaining half wave rectified voltage from an alternating source.

Abstract: A protective circuit for a transistor amplifier is disclosed which includes a load impedance detecting circuit provided between an output terminal of a transistor amplifier and a load terminal, a circuit for detecting an abrupt surge voltage of a voltage source for the amplifier and a muting circuit are provided between an input terminal of the amplifier and a reference point, the muting circuit being operative to limit an input signal applied to the input terminal of the amplifier in response to output signals of the load impedance detecting circuit. A protective circuit having a thermal sensing circuit for detecting a temperature rise of an output transistor above a predetermined level which shuts off the amplifier is described as one embodiment.

Abstract: The amplitude is detected of both the input and output signals of the circuit (such as an audio amplifier) it is desired to protect. When, for example, a short circuit occurs across the load being driven, there is a sudden change in the ratio of these amplitudes and in response to this change, the signal to the output driver stage of the circuit is shunted to ground.