Abstract: A circuit arrangement for protecting an input of an integrated circuit (14) fed from a supply voltage source from overvoltages contains an input (26) which is connected to the input (12) of the integrated circuit to be protected. A four-layer diode (T1, T2) having two control terminals lies in parallel with the input (12) to be protected and a negative feedback resistor (R1) is connected in series with the four-layer diode. Connected to the one control terminal of the four-layer diode (T1, T2) is the control terminal of a controllable current drain element (T4) which is connected in parallel with the four-layer diode (T1, T2). For applying a reference voltage, the junction point of a series circuit comprising a diode (T3) and a constant current source (S) lying between the supply voltage and ground is connected to the other control terminal.

Abstract: In one embodiment, the threshold voltage of the electrostatic protection circuit is selectively raised above the power supply voltage by the inclusion of a plurality of serially connected diodes connected between the power supply voltage and a discharge reference rail. The serially connected diodes become forward biased when a voltage applied to the rail is above the power supply voltage by a voltage equal to the sum of the various voltage drops across the serially connected diodes.The various input pads of the integrated circuit are connected to an anode of an associated diode, wherein the cathode of the associated diode is connected to the discharge reference rail, rather than directly to V.sub.DD as in the prior art. The anodes of each of these diodes are also connected to the device to be protected within the integrated circuit.

Abstract: A mechanically normally open low voltage switch is connected between ground and the high impedance input of a low voltage electronic circuit fed by a low voltage source through a low impedance resistor. With the switch open, current flows into high impedance input of the electronic circuit to provide the electrically normally closed function. When the switch is actuated to the closed position, the high impedance input is pulled down to ground to provide the switch open function.

Abstract: A temperature limiting device for connection across a common heater which senses the critical temperature of the heater to trip circuit breakers and thereby disrupt power to the heater when the critical temperature exceeds a predetermined value. The device includes an SCR or triac connected across power lines to the heater and which is triggered by a comparator monitoring the output of an integrator circuit. The input to integrator circuit is connected to the output of a thermocouple device. Upon the critical temperature of the heater exceeding the predetermined value as determined by the integrator and comparator circuits the SCR or triac is fired so as to short the voltage lines and thereby open the mechanically resettable circuit breakers.

Abstract: A single-channel shunt-diode safety barrier for energizing a 2-wire transmitter, particularly for use in process control, incorporates within the barrier a floating d.c. power supply or its equivalent to enable the barrier to deliver into an earthed load a direct current substantially equal to that which it draws from the transmitter. The floating d.c. power supply is preferably derived from an external d.c. power source via a transformer or diode-pump circuit within the barrier itself. The barrier is enabled to pass superimposed digital or frequency signals in both directions to and from the transmitter.

Abstract: A digital differential signal transmission apparatus is provided in a transmission line connecting a device (3) requiring an explosion-proof structure with a differential driver (101) or differential receiver (102). A shunt diode-type safety device (16) is inserted in order to realize an essential safe explosion-proof structure. High impedance transmission lines, which transmit and receive a single end signal, are employed as the transmission lines. Another shunt diode-type safety device (408) is inserted in a power supply line (143) connected to transmitting equipment (405, 406) on the side of the abovementioned device.

Abstract: A radio frequency limiter having a radio frequency power divider having an input and a plurality of outputs; at least one diode connected in shunt with each one of the outputs of the power divider; and, a power combiner having an output and a plurality of inputs, each one of such inputs being connected to a corresponding one of the outputs of the power divider. With such arrangement, the insertion loss of such limiter is reduced compared to a limiter having a like number of diodes connected in shunt at a common point of a single transmission line. Therefore, the reduced insertion loss means that the impedance matching circuit required will not limit the maximum operating frequency to the degree an impedance matching circuit of similar complexity will limit the maximum operating frequency required for a limiter having the same number of diodes but using a single transmission line.

Abstract: An integrated circuit is disclosed having a thermal shutdown capability. A single chip bonding pad is coupled to a circuit that will operate the bonding pad at a low potential for normal conditions and will pull it high when a temperature threshold is crossed. Thus, the normally low bonding pad provides a temperature flag. The bonding pad is also coupled to a latch that will hold it high and to a lockout circuit that acts to disable the heat producing chip circuitry. Therefore, when the bonding pad is once driven high the circuits are locked out and will remain out until a start up command is present. This is achieved by either momentarily removing the power supply or by pulling the bonding pad low. Both manual and computer control of the circuit is disclosed.

Abstract: A differential current protection circuit breaker that operates as a magnetic amplifier has a secondary winding connected in series to a complex, predominately capacitive measuring impedance and a square wave generator. An evaluating circuit is connected at a tap and is actuated along a tripping device and a switch latch of a switching contact device. The evaluation circuit is blocked by a sensor that responds to extraneous current surges or voltage surges during a predetermined response time. A blocking device in the tripping device responds to the signals from the sensor.

Abstract: Zinc oxide surge arresters are used to replace capacitive elements for voltages below the pick-up voltage of the surge arrester. Advantageously, the surge arresters may be provided in an alternating current network to provide a high degree of protection against transient disturbances without increasing cost.

Abstract: A filament bypass circuit for use with a string of lamps in series capable of continuing current flow when a lamp in the string fails. Each lamp is provided with a shunt circuit consisting of a series circuit of a diode and a silicon bilateral voltage triggered switch. The switch becomes conductive upon the application of a substantial increase in voltage from the A.C. source and remains conductive until there is an interruption of current flow or current flow drops below its required holding value. The diode insures that during continued operation after a failure there will not be an excessive voltage applied to the remaining lamps, and also serves as an indicator of a failed lamp.

Abstract: An overcurrent protection circuit wherein excessive current flow to current handling components triggers a programmable unijunction transistor which activates a crow-bar device to clamp off current flow through the current handling components. The overcurrent protection circuit finds utility in protecting solid state circuits from overcurrent situations, and is characterized by rapid response time on an order of less than one microsecond.

Abstract: Disclosed herein is a regulator circuit for regulating the charging of a battery from a source of alternating current wherein the regulator circuit includes a rectifier having first and second pairs of terminals. Alternating current, applied to the first pair of terminals, is converted to a unidirectional charge current for application to the battery through the second pair of terminals. Circuitry, responsive to the voltage at the first pair of terminals, inhibits the generation of the charge current when the voltage at the first pair of terminals reaches a predetermined threshold. Additional circuitry, also responsive to the voltage at the first pair of terminals, provides a low impedence path across the second pair of terminals. Upon the occurrence of an overvoltage condition, the production of charge current by the rectifier is inhibited and any capacitance coupled to the charge current output circuit is discharged through the low impedence path provided across the second pair of terminals.

Abstract: Varistor fuse element for protecting an electric circuit against overvoltages, including a thermal fuse, a varistor combined with the thermal fuse for for tripping the thermal fuse with joulean or ohmic heat losses of the varistor, first and second conductors for supplying current to the fuse element, and first and second switch contacts each being connected to a respective one of the conductors for bridging the varistor, the contacts being closed when the thermal fuse is tripped by the varistor.

Abstract: A power supply circuit includes a battery power source connected by a switch to the input of a DC to DC converter. The output of the DC to DC converter is connected to a filter capacitor and a load. A crow-bar is connected to the input and the output of the DC to DC converter. The crow-bar shorts the output to ground to discharge the capacitor when the voltage at the input drops to a predetermined value.

Abstract: A synchro power amplifier and control circuit for an inductive load has a plurality of synchro leg amplifiers connected to the load. Each amplifier has an interstage transformer for deriving samples of current drawn by the load. A multiplicity of capacitors are respectively connectable in parallel with the (load) upstream of the amplifiers by switches in a circuit 10 responsive to the voltage/current phase angle of the power driving the load, to compensate for the inductance of the load.

Abstract: A power line transient surge suppressor circuit features a nonlinear surge-bypassing network connected to bypass line surges around electrical loads connected to circuit output terminals. A fuse is inserted in series with the network, and blows in the event of short-circuit failure of a regulator device in the network. A thermal cut-out preferably of the irreversibly actuated type is inserted in series with the suppressor circuit input. A current-limiting heater resistor connected in parallel with the fuse supplies heat to trip the cut-out after the fuse blows, thereby permanently terminating power output to the loads. A similar suppression network is provided for the earth lead in three-wire systems.

Abstract: A protective circuit for reducing subsynchronous natural resonant frequency signals in a multiphase power supply system includes a damping resistor connected in series with each phase winding of the system. A resonant circuit tuned to the rated line frequency of the system is connected in parallel with each resistor so that signals having frequencies other than the rated line frequency will be damped by the resistors. An inductor can also be placed in parallel with each resistor to maximize the damping effect of each resistor at predetermined subsynchronous frequencies.

Abstract: A secondary arc extinction device in an electric power system, including a bus bar; an electric power line connected to the bus bar; protective relaying means connected to the bus bar; first reactance means having two terminals, one terminal of which is connected to the electric power line; a transformer having a primary winding and a secondary winding connected between the other terminal of the first reactance means and ground; second reactance means connected to the secondary winding of the transformer; and means for controlling the second reactance means in response to the protective relaying means.

Abstract: Transmission lines have both their terminals connected with bus lines through breakers, respectively, and connected to earth through earth switches, respectively. Protecting relay devices are fed with not only the outputs of voltage transformers and current transformers but also the contact signals made coactive with the breakers and earth switches at the terminals considered. Those contact signals are transmitted through signal transmission devices to the other terminals, and the contact signals of the breakers and earth switches at the other terminals are transmitted. The protecting relay devices detect the fault of the transmission lines, if any, to trip the breakers and to confirm the open states of the breakers from the breaker contact signals of the terminals considered and the other terminals thereby to close the earth switches.

Abstract: A three-phase power supply has a current transformer in each power line. The transformer secondary winding is connected to a load. Generally, the load is a control means responsive to the current being sensed. A triac in parallel with the secondary winding and load has its gate connected by a voltage sensitive circuit to sense the corresponding secondary winding voltage and to conduct and protect the transformer in the event of load loss. The gate circuit includes a metal oxide varistor and a linear resistor in series connected in parallel with the secondary winding. A second linear resistor is connected to the common node of the first linear resistor and metal oxide varistor. The second linear resistor is in series with a diac and connects the gate to the common node of the varistor and first resistor. A trigger capacitor is connected between the common node of the second resistor and diac and the opposite end of the first linear resistor.

Abstract: A safety power cutoff arrangement is disclosed for appliances which utilize membrane panel switches on their control panels causing electrical power to the appliance to be shut off in the event of damage to the control panel. The safety cutoff arrangement comprises a conductive track pattern formed over the outermost circuit sheet forming the membrane switch and interrupter circuitry which requires the continuity of the conductive track pattern to be maintained for electrical power to be continued to be supplied to the appliance circuitry. In the event of damage to the control panel, breaking of any segment of the conductive track pattern results in the interrupt safety circuit cutting off power to the appliance.

Abstract: A high-voltage crowbar circuit continually senses the load impedance and crowbars the output voltage applied to a load if the load impedance falls below a selected value. A differentiator circuit at the load senses variations in load voltage and can trigger the crowbar operation if the voltage variation as a function of time exceeds a preselected load.

Abstract: A solid state relay is disclosed which is failsafe in the sense that it is prevented from failing in a closed circuit condition. The relay comprises a main switch adapted to be connected in series with a load and voltage source and responsive to relay opening and closing signals. A secondary switch is connected in parallel with the load and is switched a sense opposite that of the main switch by the relay opening and closing signals. If the main switch fails to open, the secondary switch is closed and the load is short circuited by it. Additionally, a fuse in series with the main switch is blown by the current through the secondary switch to latch the relay in the open circuit condition. Self-checking circuits are provided to latch the relay an open circuit condition if there is any circuit failure.

Abstract: A fault detector for detecting shoot-through conditions in series connected solid state rectifiers (326, 329) of a power inverter (314) is disclosed. A capacitor (311) discharges when a shoot-through occurs and the discharge current is detected by a current transformer (315). An SCR (317) is gated on by the detector to short circuit the DC bus (327, 328) and prevent damage to the solid state rectifiers (326, 329).

Abstract: A high speed fault diverter switch is connected near the input side of a gas-insulated substation. The switch is normally open and is used in response to arcing anywhere within the substation to connect the gas-insulated high-voltage conductor to ground for each phase of the system at high speed to divert the fault current to ground.

Abstract: In a series capacitor transmission system the protective bypass device has a force firing arrangement responsive to an applied signal for causing the series capacitor bank to be bypassed rapidly, such as within three cycles, for reducing subsynchronous oscillation effects on generating equipment connected with the transmission system. A capacitive potential device supplies power to energize a firing control circuit with a pulse transformer placing high frequency or pulse voltage across the protective device for rapid bypassing. The bypass device may be a protective spark gap as is normally present for protection of the capacitor bank against overvoltages.

Abstract: Apparatus for detecting current flow in any one or more of the three lines of a three phase electrical system which have been connected together by means having negligible impedance which comprises three current transformers which may be magnetically coupled to the lines and a further transformer for combining the outputs of the current transformers. The further transformer is connected to an amplifier and a rectifier and the rectified voltage is used to control a visual and audible alarm system to indicate the presence of current flow in one or more of the lines. The rectified voltage may also be used to prevent re-opening of a switch which is used to interconnect the lines.

Abstract: A temperature responsive resistor is thermally connected to a body of metal oxide varistor material in transient suppression and other applications. In the event of excess energy dissipation in the varistor, the temperature of the thermally responsive resistor increases to provide a trigger signal to a triac or other similar electronic switch which may be utilized to provide an alarm, provide increased cooling to the varistor body, to divert, or limit current flow from the varistor.Current flow through the temperature responsive resistor may be provided from a third terminal on the metal oxide varistor in which case the circuit is responsive to both total energy dissipation and peak energy dissipation levels in the varistor.

Abstract: In a gate input circuit for insulated gate field effect transistors, an insulated gate field effect transistor of depletion type is used, whose drain electrode (or source electrode) is connected to one terminal of a power source and whose source electrode (or drain electrode) is short-circuited with the gate electrode and connected to an input terminal of the gate input circuit through a resistor.