Abstract: A protection apparatus (48) is provided which in addition to protecting electronic equipment (5) from overvoltage transients is also able to provide an indication of whether or not said transients are due to impedances associated with poor earthing. In one embodiment the protection apparatus (48) includes an input terminal (42), an output terminal (60) and a ground reference terminal (62) with a transient blocking unit (50) arranged to isolate the output terminal (60) in response to the destructive transient voltages. A gas discharge tube (46) is provided to conduct transient currents associated with the destructive transient voltages to the earth reference connection point (62); and an indicator (58), such as a fuse or circuit breaker is placed in series with the transient blocking unit (50) to indicate the presence of a voltage resulting from an interaction of the transient currents with an earthing impedance.

Abstract: A protection system in which a shunt protection device at the interface terminals is optically triggered by sensor components within the circuit. This permits a variety of appropriate overvoltage detection thresholds to be defined at different nodes within the circuit. Preferably the shunt protection device is combined with one or more series protection devices which interrupt overcurrent.

Abstract: A differential mode surge protection apparatus includes first and second solid state protection devices in series between respective input and output connection points. The apparatus may be provided in conjunction with a common mode protection apparatus such as an isolation transformer. Alternatively, the apparatus may be provided integrated into a single miniaturized protection package. In a preferred embodiment, the apparatus includes a surge arrestor arranged to supplement protection conferred by the first and second solid state protection devices. The surge arrestor is capable of being triggered prior to breakdown of either the first or second solid state protection devices. The apparatus may be incorporated into digital processing cards such as LAN cards and also into cables to conveniently provide differential mode protection.

Abstract: An apparatus and method for temperature-dependent transient blocking employing a transient blocking unit (TBU) that uses at least one depletion mode n-channel device interconnected with at least one depletion mode p-channel device. The interconnection is performed such that a transient alters a bias voltage Vp of the p-channel device and a bias voltage Vn of the n-channel device in concert to effectuate their mutual switch off to block the transient. The apparatus has a temperature control unit that is in communication with the TBU and adjusts at least one of the bias voltages Vp, Vn in response to a sensed temperature Ts, thereby enabling the apparatus to also respond to over-temperature. In some embodiments the p-channel device is replaced with a positive temperature coefficient thermistor (PTC). The temperature control unit can use any suitable circuit element, including, among other a PTC, resistor, negative temperature coefficient element, positive temperature coefficient element, transistor, diode.

Abstract: An apparatus and method for enhanced transient blocking employing a transient blocking unit (TBU) that uses at least one depletion mode n-channel device interconnected with at least one depletion mode p-channel device. The interconnection is performed such that a transient alters a bias voltage Vp of the p-channel device and a bias voltage Vn of the n-channel device such that the p- and n-channel devices mutually switch off to block the transient. The apparatus has an enhancer circuit for applying an enhancement bias to a gate terminal of at least one of the depletion mode n-channel devices of the TBU to reduce a total resistance Rtot of the apparatus. Alternatively, the apparatus has an enhancement mode NMOS transistor and a TBU connected thereto to help provide an enhancement bias to a gate terminal of the enhancement mode NMOS.

Abstract: Merged devices for transient blocking. A pass transistor is placed so that its body potential drives the gate of a depletion-mode JFET-type blocking transistor. Thus a transient which appears on an external terminal is very rapidly propagated to shut off the blocking transistor, before large numbers of carriers can be injected. Preferably a shunt device is also used to drop high potentials which may appear at the same time. This connection can be particularly useful in power or data input terminals.

Abstract: A protection apparatus (48) is provided which in addition to protecting electronic equipment (5) from overvoltage transients is also able to provide an indication of whether or not said transients are due to impedances associated with poor earthing. In one embodiment the protection apparatus (48) includes an input terminal (42), an output terminal (60) and a ground reference terminal (62) with a transient blocking unit (50) arranged to isolate the output terminal (60) in response to the destructive transient voltages. A gas discharge tube (46) is provided to conduct transient currents associated with the destructive transient voltages to the earth reference connection point (62); and an indicator (58), such as a fuse or circuit breaker is placed in series with the transient blocking unit (50) to indicate the presence of a voltage resulting from an interaction of the transient currents with an earthing impedance.