Abstract: The invention concerns an anode voltage sensor of a vertical power component selected from the group consisting of components called thyristor, MOS, IGBT, PMCT, EST, BRT transistor, MOS thyristor, turn-off MOS thyristor, formed by a lightly doped N-type substrate (1) whereof the rear surface (2) having a metallizing coat corresponds to the component anode. Said sensor comprises, on the front surface side, a substrate zone (12) surrounded at least partly by a P-type region with low potential in front of an anode potential, said zone (12) being coated with a metallizing coat (M) in ohmic contact with it, whereon is provided an image of the anode voltage.

Abstract: A power amplifier module is provided with a function of protecting an amplifying device against destruction caused by a standing wave by reflection from an antenna end in load variation. Increase in base current from idling current of a final stage amplifying portion GaAs-HBT in load variation is detected and canceled and collector current is restrained to thereby prevent an increase in output and prevent destruction of GaAs-RET. By also using a function of successively lowering idling current when power source voltage is elevated and a clipping function of diodes connected in parallel with output stage GaAs-RET, voltage as well as current more than necessary are avoided from being applied on the output stage GaAs-RET.

Abstract: A ground fault circuit interrupter for use on a circuit having an AC power source electrically connected to a load circuit via hot and neutral lines. The ground fault circuit interrupter having at least a pair of switching components forming part of the circuit for opening the circuit upon occurrence of a ground fault. The switching components are electronic semiconductors, preferably MOSFETs, which permit substantially instantaneous switching. In addition, preferably the ground fault circuit interrupter includes a pair of redundant switching channels so that failure of any one component does not prevent the ground fault circuit interrupter from properly opening the circuit upon detection of a ground fault.

Abstract: According to the present invention, for a module in which a plurality of integrated circuit devices are mounted in parallel, the inductance generated by the unit length of a branched signal line on a motherboard is so set that it is smaller for a branched signal line a longer distance from its branching point to its distal end, and is so set that it is larger for a branched signal line having a shorter distance from its branching point to its distal end, so that the time required for transmission of a signal from the branching point to the distal end of each branched signal line is the same.

Abstract: A protection circuit (10) is formed to protected a load (11) when a short circuit develops during operation of the load (11). A load transistor (18) is formed to couple the load to a voltage return terminal. A disable transistor (19) is formed to disable the load transistor (18) when a short circuit occurs.

Abstract: The present invention provides a short circuit power limiter circuit having a current sensor and a power limiter. The short circuit sensor sends a short circuit flag signal to the power limiter when the short circuit sensor detects a short circuit condition in a target circuit. The power limiter then reduces the power consumption of the target circuit. In a specific example, the power limiter toggles a particular portion of the target circuit on and off to reduce the circuit's average short circuit power consumption. This cycle is repeated as long as a short circuit condition exists.

Abstract: A semiconductor fuse for electrical consumers (2) is disclosed, in which a semiconductor switch (3) is disposed between the battery (1) serving as a current- or voltage source and the consumer (2). Parallel to the semiconductor switch (3), there is a short circuit-proof bypass (4) with an integrated wakeup circuit (5), which cooperates with the semiconductor switch (3).

Abstract: A power module including a self arc-extinguishing type semiconductor such as an IGBT and having a function to protect the semiconductor, i.e., to protect the IGBT against a short-circuit current. Even the IGBT having a collector-emitter saturation voltage VCE (sat) set low can be protected against the short-circuit current, by charging a collector-gate junction capacitor (13) quickly, when a sense current IS to flow through a current sense exceeds a set value, to raise a collector voltage VCE quickly thereby to prevent a collector current IC from increasing, by keeping a gate voltage VGE of the IGBT (12) at a voltage rather higher than a threshold voltage, and by turning OFF the IGBT (12) after a predetermined time.

Abstract: A discharge interrupt circuit and method is directed to short circuit protection for an electronic circuit that includes a load regulation device that is arranged to normally provide an output current. The discharge interrupt circuit detects a short circuit condition by monitoring the voltage across the load regulation device. When a short circuit is detected, a logic circuit within the discharge interrupt circuit latches the short circuit condition in a memory circuit and disables the load regulation device such that the output current is interrupted from flowing. The logic circuit re-enables the load regulation device when the logic circuit has determined that the device has been deactivated. A time-out circuit can also be used add an additional delay between the load regulation device being disabled and re-enabled. The discharge interrupt circuit provides short circuit protection with power supply voltages less than 1V.

Abstract: A solid state fuse type protective circuit is provided in which a series MOSFET is connected in series with the load and its voltage source and a shunt MOSFET is connected in parallel with the load. A control circuit turns the series MOSFET on and the shunt FET off under normal operation; and turns the series FET off and applies a turn on signal to the shunt FET under a fault condition. An indicator LED is connected across the series FET and turns on when the series FET turns off.

Abstract: A bipolar junction transistor (BJT) used as a synchronous rectifier (SR) that is driven and controlled by an electronic circuit, such that when the collector-emitter voltage (VCE) is above an offset voltage (VOS) the circuit drives the base of the SR BJT with a base current proportional to the difference between VCE and VOS, turning the SR BJT on with a base current proportional to the collector current. When the VCE of the SR BJT falls below VOS the drive circuit turns on a second transistor coupled between the base and collector of the SR BJT to turn the SR BJT rapidly off and maintains it in the off state as the collector voltage reverses. When the VCE of the SR BJT is exceeds a threshold voltage above the normal conduction VCE range, the control circuit increases the base drive current to accelerate the SR BJT turn-on process.

Abstract: A circuit that protects a current shunt or any analog measuring circuit without the implementation of fuses. In a particular embodiment, a circuit comprises a current shunt and a plurality of transistors that may be configured to function as a fuse. One of the transistors may be deactivated once the input voltage exceeds a negative threshold voltage. The other transistor may be deactivated once the input voltage exceeds a positive threshold voltage. By deactivating the transistors once the input voltage exceeds a negative or a positive threshold voltage, the transistors are configured to function as a fuse and provide input protection for a current shunt or for any analog measuring circuit. In another particular embodiment, a circuit provides protection for a first and second current shunt where the second current shunt is less in resistance than the first current shunt. The circuit further comprises a plurality of transistors that may be configured to function as a fuse.

Abstract: This circuit is inserted between a terminal (RGB) and a line (LI). The signal of the input terminal (RGB) is applied to the base of a bipolar amplifier transistor (T2) mounted with a top load (LR1) and a bottom load (LR2). A series transistor (T1) mounted in series in the main signal path has its collector wired up as an electrode for receiving the input signal, its emitter feeds a line (LI), and its base is linked by a resistor to the collector of the second transistor.

Abstract: A solid state safety relay comprises: a first driver circuit; a second driver circuit; a charge disconnect transistor coupled to the first driver circuit and configured to control the flow of current along a current path; a first discharge disconnect transistor coupled to the first driver circuit and configured to control the flow of current along the current path; and a second discharge disconnect transistor coupled to the second driver circuit and configured to control the flow of current along the current path. A method of isolating an energy source from a circuit current path, comprises: turning off a first discharge disconnect transistor coupled to the circuit current path; and turning off a second discharge disconnect transistor coupled to the circuit current path to permit isolation of the energy source from the circuit current path if either one of the first discharge disconnect transistor or the second discharge disconnect transistor fails.

Abstract: A buck converter has an input circuit for receiving an input signal, a controller connected to and controlling the input circuit, a switch controllable by the controller for switching on/off, a current storage element connected to the input circuit and the switch, and an output voltage storage element connected to the current storage element for connecting in parallel with a load. In a charging phase, the controller causes (a) the input circuit to allow the input signal to pass through for provision to the load via the current storage element and (b) the switch to switch off (becoming an open circuit). In a discharging phase, the controller causes (a) the input circuit to decouple from the input signal and (b) the switch to switch on (become a short circuit), so that (c) current flows within a loop formed by the switch and the current storage element.

Abstract: A method for performing a short-circuit and overload disconnection with a semiconductor component includes the steps of providing a semiconductor component having a drain, a source and a gate. The semiconductor component has a gate-source voltage applied thereto, a current flowing therethrough, and a voltage dropping between the source and the drain. The gate-source voltage at the semiconductor component is adjusted, in dependence of the current flowing through the semiconductor component, such that, after charge carriers in the semiconductor component are depleted, the voltage dropping between the source and the drain assumes a highest possible value still uncritical for the semiconductor component and for a circuit to be disconnected. An algorithm is used for the step of adjusting the voltage dropping between the source and the drain.

Abstract: A plant for transmitting electric power which employs a first combination of a turn off semiconductor and controllable semiconductor connected in antiparallel and a second combination of a turn off semiconductor and antiparallel wherein the first combination is alternately conducting and blocking current for producing an alternating current output and the second combination is conducting during normal operation of the plant. When a fault occurs, a disconnect switch opens and separates the plant from other plants located on the network.

Abstract: A fuseless DC-DC converter is provided to protect a circuit from overcurrent without involvement of a protective fuse. This is accomplished by providing a load circuit in the converter that includes a first overheat self-interruption-type semiconductor switch in series between a DC power supply and a load, and a reference circuit including a second overheat self-interruption-type semiconductor switch in parrallel with the first switch, and a reference resistor with one end connected to the source of the second switch, and the other end grounded. Also included is a comparator circuit that compares the source voltage of the first switch with a reference voltage applied to the source of the second switch, and thereby determines if the circuit has overcurrent. If overcurrent is detected, the results from the comparator circuit are used by a power supply controller to deactivate the semiconductor switch.

Abstract: In a circuit arrangement for monitoring an electronic switch provided for controlling a load and current flown through the load during turn-on intervals for driving the load, the switch has a substantially linear resistance behavior during parts of its turn-on state and the operating point of the switch is located in this part of the turn-on state during the load control. The circuit arrangement comprises a modulation signal generator for generating a modulation signal for modulating the load current flowing through the electronic switch. A first voltage measuring device measures the first voltage drop across the electronic switch caused by the modulation signal. A second voltage measuring device measures the voltage drop across the electronic switch caused by the load current, and an evaluation unit determines the load current from the modulation signal and the first and second voltage drops.

Abstract: The present invention discloses a circuit and method for detecting a fault current in a circuit containing a power transistor. A comparator in communication with a parasitic inductance is utilized to sense the excessive change in current through the power transistor. When the voltage magnitude through the parasitic inductor exceeds a predefined limit, the comparator triggers a gate drive circuit. The gate drive circuit is in communication with the power transistor. The gate drive circuit shuts off the power transistor when the predefined limit is reached. Thus, the present invention is capable of reacting quickly to fault currents through the power transistor thereby protecting the transistor and other circuit components from damage.

Abstract: In a switch driver, a pnp transistor turns ON or OFF the passage of the charging current. Resistors are commonly connected to a base of the pnp transistor. Npn transistors are provided in such a way that their collectors are connected to each of the resistors and their emitters are grounded. Bases of each of npn transistors are connected to a control unit. This control unit subsequently turns ON each of the npn transistors so that a base current required for turning ON the pnp transistor flows. Since the base current rises slowly, an abrupt rise of the switching current in a switch driver can be prevented.

Abstract: A circuit for detecting and automatically responding to ground faults. A passive protection PTC resistor is coupled in series with an active protection switch, the active protection switch being controlled by a control circuit to open the switch when excess current is detected to be flowing in the common path of one of the channels. Floating and grounded versions are described.

Abstract: A system for controlling and monitoring operation of an electrical system is described. The system includes a fault protection device, for example, a circuit breaker, that is connected to the electrical system to provide fault isolation. The system also includes a protection system that includes an interface and a logic system connected to the electrical system. The logic system is connected to the interface and controlled by a processor to receive input from the electrical system and input from a user through the interface. The logic system operates the fault protection device when the received input from the electrical system indicates a fault event. Additionally, the logic system indicates information relating to operation of the electrical system through the interface.

Abstract: In an electric power switch circuit with an overcurrent or overheating protection function, unnecessary ON-OFF cycling is prevented. A MOSFET is used as an electric power element for energizing a load according to a control signal. A temperature detector detects the temperature in the neighborhood of the MOSFET, and a control unit opens a switch, interrupting input of the control signal to the MOSPET when the temperature detected by the temperature detecting means is higher than the predetermined temperature. An interruption status retaining device maintains the interruption of the control signal, preventing repetitive ON-OFF cycling.

Abstract: A circuit protection device for protecting an electrical load includes a three-terminal switch element such as a bipolar, or junction or metal-oxide-semiconductor field effect, transistor and a positive temperature compensation (PTC) resistor. In several embodiments the PTC resistor is in series with the current-carrying electrodes of the transistor. In other embodiments the PTC resistor, or a second PTC resistor, is connected to a control element of the transistor. Both DC and AC load-protection circuits are described.

Abstract: The switching functions of switching a load on and off in normal operation and in fault operation are implemented in a simple manner in an electronic branch circuit switch, which is advantageously made with silicon carbide semiconductor switching elements and has a potential-free control device, a device for detection and immediate shutoff in the event of a short-circuit, and a protection device for detection and shutoff against overload currents, as well as an overvoltage limiting device.

Abstract: A short-circuit protection circuit, particularly for power transistors, contains a first circuit for mirroring the output current of a power transistor which is parallel-connected to the power transistor, and a second mirroring circuit which is series-connected to the first mirroring means and is adapted to emit a current which is correlated to the current mirrored by the first mirroring circuit, for comparison with a reference current. The result of the comparison determines the need to intervene or not on the power transistor. The short-circuit protection circuit may also contain a circuit for sensing the voltage drop across the power transistor which is parallel-connected to the power transistor and to the first mirroring circuit, in order to adjust minimum and maximum values of the current in output from the power transistor, as a function of the voltage that is present across the transistor.

Abstract: A power cut-off device comprises first and second electronic switching devices (FETs T2 and T1) which are cross-coupled so that when one switching device is on the other is off and vice versa, and a load (11) to be protected is connectable in series with the first switching device (FET T2). If the current through the first switching device (FET T2) exceeds a certain value, caused for example by a short circuit at the load, the second switching device (FET T1) is turned on to turn the first switching device off.

Abstract: A four-terminal MOSFET, in which no combination of the source, drain, body and gate terminals are permanently connected together, is used as a synchronous rectifier capable of blocking an excessive current in a switching mode DC--DC converter resulting from a short-circuited load. In an N-channel version of the synchronous rectifier, the MOSFET body terminal is normally connected to the inductor in the DC--DC converter and is grounded when an overcurrent condition is detected. In a P-channel version of the synchronous rectifier, the MOSFET body terminal is normally connected to the converter output and is connected to the inductor when an overcurrent condition is detected. In addition, the voltage output by the inductor may be clamped using a zener diode or a snubber capacitor. A MOSFET body bias switching circuit is driven by overcurrent detection circuitry that may also be used to turn off the synchronous rectifier MOSFET gate.

Abstract: A device (1) for supplying electric power to a load (4) connected to the device (1) in a power-on mode comprises a driver stage (7), a control unit (9), adapted to supply turn-on pulses to the driver stage (7), and an output stage (12) with a switching transistor (1) which can be driven into its conductive state for a time interval (T.sub.EIN) by the driver stage (7) in the power-on mode when turn-on pulses occur, and which can be driven into its non-conductive state after expiry of the time interval (T.sub.EIN), the driver stage (7) being also adapted to monitor the operating temperature (T.sub.S) of the switching transistor (11) and to activate a power-off mode when the operating temperature (T.sub.S) of the switching transistor (11) exceeds a first limit temperature (T.sub.G1), in which power-off mode the switching transistor (11) is permanently driven into its non-conductive state by the driver stage (7) in spite of the occurrence of turn-on pulses (I.sub.

Abstract: A trigger circuit for a field-effect-controlled power semiconductor component has a controllable gate resistor for the power semiconductor component, which has low impedance in a normal situation and is switched to high impedance in the event of a short circuit. As a result, the turn-on time in the normal situation is shortened, and limiting the gate-to-source voltage of the power semiconductor component in the short-circuit situation is made possible.

Abstract: An overcurrent prevention circuit which removes noise upon transmission of a signal over a signal line between two devices for which different power supplies are used and prevents overcurrent from flowing through the signal line to prevent an otherwise possible breakdown of the devices or an associated element. Current from a waveform outputting terminal to an external signal line is detected from a voltage drop across a resistance part. Then, in response to a result of the detection, an N-channel D-type MOS transistor which supplies current of an output signal to the waveform outputting terminal is controlled between on and off to interrupt supply of power. Consequently, no overcurrent flows out from the waveform outputting terminal, and a clamp diode for removing noise connected to the waveform outputting terminal does not suffer from a breakdown by overcurrent.

Abstract: Apparatus and method for limiting current in a direct voltage network of a HVDC power distribution system. A direct voltage network is connected to an alternating voltage network through a VSC-converter. At least one parallel connection including a semiconductor switching element is connected in series with the direct voltage network. A surge diverter is connected in parallel with the semiconductor switching element. During a high current condition in the direct voltage network, the switching element is switched off interrupting the current flow which is then diverted through the surge diverter which reduces the current flowing in the direct voltage network. By inserting a plurality of parallel connections, and selectively turning off a number of the semiconductor switching elements, a number of different levels of over current conditions in the direct voltage network may be controlled.

Abstract: For use with a protection circuit having an in-rush current control element that controls in-rush current into a power converter, a control circuit, a method of controlling the in-rush current control element and a power supply employing the control circuit and method are provided. In one embodiment, the control circuit includes: (1) a sensor, coupled to the in-rush current control element, that senses an in-rush current through the in-rush current control element and produces an intermediate signal and (2) a controller, coupled to the sensor and the in-rush current control element, that controls the in-rush current control element to limit the in-rush current when the intermediate signal exceeds a first reference current signal and to substantially interrupt the in-rush current when the intermediate signal exceeds a second reference current signal.

Abstract: A device for counting the edges of electric pulses is disclosed and comprises a first capacitor connected in series with a pump circuit, which comprises a first resistance in series with a first diode connected in parallel with a second resistance, and a second capacitor connected in parallel with the first resistance. When a voltage, which is caused by one of the edges of an electric pulse, is applied across the first capacitor and the pump circuit, the first and second capacitors are charged in series with a charge that is essentially determined by the second capacitor. A first input of a comparator is connected to the connection point between the first capacitor and the pump circuit and a second input of the comparator is connected to a comparison potential, in order to indicate that a given approximate number of pulses have been counted when the voltage across the first capacitor exceeds a threshold level determined by the comparison potential.

Abstract: The current flowing in an output field effect transistor is sensed by a parallel circuit arrangement which derives a sensed current representing the current flowing in the output transistor. The parallel circuit arrangement comprises series-connected CMOS transistors which are connected together in order to derive a current output which is representative of the load current through the output transistor. In a short circuit protected output buffer, the sensed current is compared with a reference current and if it exceeds the reference current the amplitude of the drive signal to the output transistor is reduced.

Abstract: A circuit protects from overcurrent conditions and detects an open electrical load. A microprocessor has at least one microprocessor terminal that is configurable as an output for generating a command signal to an electrical load and as an input for monitoring the condition of the electrical load. A first transistor is operatively connected to the microprocessor terminal and has an output to be connected to the electrical load. The first transistor has ON and OFF states. A second transistor is powered from a power supply and is connected to the first transistor and the microprocessor terminal. The second transistor is operative to generate an output logic signal back to the microprocessor and to latch the first transistor into one of either ON or OFF states under normal load conditions responsive to the receipt of a command signal from the microprocessor, and to maintain the first transistor in an OFF state upon an abnormal overcurrent condition through the first transistor.

Abstract: A control circuit for providing fast turn-off of a PNP transistor with output transient protection. An embodiment of the invention provides a current amplifier coupled between a positive voltage supply line and the base of a PNP switching transistor and an input device for providing an input current to the current amplifier. The current amplifier provides a transitory reverse drive current to the base of the PNP switching transistor. The current amplifier and the input device both include transient blocking junctions that block current flow from a positive voltage transient in excess of the positive supply voltage. The current amplifier is a PNP drive transistor in the preferred embodiment. The PNP drive transistor provides a transitory reverse drive current to the base of the PNP switching transistor.

Abstract: A self-excitation type switch power supply unit with overcurrent protection. For adopting a simple and reliable current negative feedback protective circuit to coordinate with a complementary bridge circuit, a positive feedback circuit without DC biasing capacitive coupling, an oscillation-starting circuit of the AC power supply, etc., so that the self-excitation type switch power supply can become a practical power supply unit with simple circuitry, small size and low cost.

Abstract: A protection circuit for a pnp-type output transistor includes a pnp-type monitor transistor through which a current 1/n (where n>1) times as high as the output current of the output transistor passes. A first, second, and third resistor are connected between the output electrode of the output transistor and ground. An output terminal is connected to the collector of the output transistor. A fourth and fifth resistor are connected serially between the output current of the monitor transistor and ground. When the voltage at the node between the fourth and fifth resistors exceeds a predetermined level, the conduction biases for the output and monitor transistors are reduced. When the voltage at the node between the first and second resistors drops below the voltage at the output side of the monitor transistor, the conduction biases are further reduced in accordance with the voltage difference.

Abstract: In an input protection circuit, a bipolar protection device is constituted of a semiconductor substrate of a first conductivity type, a first diffused layer of a second conductivity type formed in the substrate and connected to an input signal pad, a second diffused layer of the second conductivity type formed in the substrate to extend in parallel to the first diffused layer but separately from the first diffused layer by a first space, and a third diffused layer of a high impurity concentration and of the first conductivity type formed in the first space in the substrate to extend in parallel to the first and second diffused layers, in junction with the second diffused layer but separately from the first diffused layer. When a backward biasing voltage is applied, the thickness of a depletion layer formed is made large, so that generation of hot carriers is minimized.

Abstract: An output circuit has multi-stage protection circuitry for protecting against different fault current conditions. The protection circuitry operates by detecting voltage changes across the output transistor of the output circuit. The output circuit comprises first, second and third switching devices. The first switching device is connected to the output device and power conditions the output signal. The second and third switching devices override the output signal and turn off the first switching device when a magnitude of current through the first switching device exceeds predetermined magnitudes for predetermined amounts of time. A protection circuit is also disclosed which has a sensing device that senses a current flow condition by sensing a voltage drop produced across two terminals of the first power conditioning transistor, the two terminals being the terminals through which the current flows. Advantageously, the output circuit utilizes highly flexible two-stage protection circuitry.

Abstract: An overcurrent detection circuit detects an overcurrent in a current path accurately and sensitively. The overcurrent detection circuit includes a first resistance element connected between first input and output terminals of the current path; a second resistance element connected to the first input terminal; a differential amplifying device connected to the first output terminal and the second resistance element; and a proportional-current output device connected to the second resistance element in series and to an output terminal of the differential amplifying device. The proportional-current output device receives an output signal from the differential amplifying device to output a proportional current with a magnitude proportional to a current flowing through the first resistance element.

Abstract: The invention relates to a method of current limitation in a direct current motor, with the following steps: in successive cycles, the motor is turned on at a predetermined place in the cycle and, after lapse of a predetermined time interval, the motor current is tested in a first test and, if found to be too high, the current is shut off; after lapse of another interval measured from the first test, the motor current is tested again during the same cycle and, if found to be too high, is shut off if it was not shut off previously; after lapse of a third interval, measured from the second test, the motor current is turned on, insofar as it was shut off at either of the two tests, and the cycle is repeated.

Abstract: A circuit configuration includes first and second terminals, a power switch having a control terminal, an electronic switch connected between the control terminal and the second terminal for turning off the power switch at excess temperature, a temperature sensor circuit connected between the first and second terminals and connected to the electronic switch, a switch device connected between the first terminal and the control terminal and a control device connected between the first and second terminals. The control device has an output side connected to the switch device. A semiconductor body includes an n.sup.- -doped base body having upper and lower main surfaces. An n.sup.+ -doped layer adjoins the lower main surface of the base body. A first region has p.sup.+ -doped regions embedded on the upper main surface and n.sup.+ -doped wells contained in the p.sup.+ -doped regions to form a vertical power MOSFET with a drain electrode connected to the n.sup.+ -doped layer.

Abstract: Circuit arrangement for current limiting, which contains, in a series path, the source-drain path of a field-effect transistor (12) and a current sensor (8) connected in series therewith. In order to achieve effective protection against momentary overcurrents, the rate of rise of the current is limited with the aid of an inductor (9) contained in the current sensor (8). A diode (11) acting as a freewheeling diode is arranged in parallel with the current sensor (8). The circuit arrangement can advantageously be used in apparatuses for supplying power to electrical telecommunications equipment.

Abstract: A method of protecting an adjustable impedance element such as a transistor controlling the power supplied to an electric motor, in particular in a motor vehicle, wherein the control of said adjustable impedance element is modified when the current passing through it exceeds a given threshold, characterized in that said current threshold is an increasing function of the voltage U.sub.M across the terminals of the motor.

Abstract: A ground fault detection and line power supply control system protects telecommunication service personnel working on line-powered telephone circuits from ground faults, without requiring that the line power supply be disconnected or shut down prior to a technician working on the line. A ground fault loop sensing current is sourced from an auxiliary DC voltage source that is separate and distinct from the line power supply. This auxiliary DC voltage source is coupled through a ground fault current sense resistor to one side of the powered line, so that detection of a ground fault condition is not dependent upon the supply of current from the potentially hazardous line supply.

Abstract: A power latch circuit for a computer is improved by the expansion of an activate control circuit to include overvoltage protection circuitry. The activate control circuit is responsive to either an activate input circuit or a feedback latch circuit to activate an activating transistor which in turn activates a series transistor providing power from a DC electric power source through a voltage regulating circuit to the computer, which is programmed to turn itself off by activating a deactivate transistor to deactivate the activating and series transistors.

Abstract: A solid state power controller for switching power on and off to an electrical load which also serves as a circuit protection device protecting the load and/or the wire connected between the load output terminal of the controller and ground from thermal damage due to current overload is shown. When a current overload exists the controller interrupts current to the load in a time inversely proportional to the square of the magnitude of the overload as shown in a trip time vs load current curve. The controller also limits the load current to a selected maximum level by controlling the drain-source resistance of power MOSFETs used for switching the power. A secondary interrupt is provided in the event that the junction temperature of the MOSFETs has risen a selected maximum level. A thermal memory feature is included for both interrupt signals. The controller is controlled by a single on/off input line and provides both a status and trip output line to indicate its state.