WO1991011840A1 - Circuit protection arrangement - Google Patents

Circuit protection arrangement Download PDF

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Publication number
WO1991011840A1
WO1991011840A1 PCT/GB1991/000120 GB9100120W WO9111840A1 WO 1991011840 A1 WO1991011840 A1 WO 1991011840A1 GB 9100120 W GB9100120 W GB 9100120W WO 9111840 A1 WO9111840 A1 WO 9111840A1
Authority
WO
WIPO (PCT)
Prior art keywords
arrangement
threshold
foldback
voltage
circuit
Prior art date
Application number
PCT/GB1991/000120
Other languages
French (fr)
Inventor
Ian Paul Atkins
Original Assignee
Raychem Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Raychem Limited filed Critical Raychem Limited
Publication of WO1991011840A1 publication Critical patent/WO1991011840A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage

Definitions

  • This invention relates to the protection of electrical circuits from voltage transients.
  • Voltage transients may be produced in electrical cir ⁇ cuits by a variety of methods, for example by lightning, electrostatic discharge or by a nuclear electromagnetic pulse. These phenomena may all induce very ' large currents on cables and structures such as aircraft and ships which can penetrate and damage electrical systems, either causing hardware damage such as semiconductor burnout or electronic upset such as transmission loss or loss of stored data.
  • Electrostatic discharges are extremely fast discharges from a capacitor such as a human body. These discharges, because they can be so local, present a great threat to the individual electronic components. Induced electrical tran ⁇ sients caused by lightning represent a threat to electrical/electronic equipment especially, but not solely, in aerospace vehicles.
  • the most severe threat to electrical and electronic equipment is the electromagnetic pulse, a typical pulse exhibiting a field strength of about 10 5 vm" 1 with an accom ⁇ panying H field intensity of 130 Am -1 (based on free space impedance of 377 ohms), a pulse width of a few microseconds and a rise time of a few nanoseconds.
  • damaging amplitudes in the pulse occur within the frequency range of 10 kHz to 100 MHz.
  • an arrangement for protecting an electrical circuit from a voltage transient which comprises a threshold foldback device arranged to be connected between a pair of current- carrying lines of the circuit, an additional overvoltage protection device connected in parallel with the threshold foldback device, the additional overvoltage protection device switching more slowly than the threshold switching device, and a capacitor having a capacitance in the range from 100 pF to 200 nF, the capacitor being connected in series with the threshold foldback device but not with the additional overvoltage protection device.
  • threshold foldback device as used herein is intended to mean a device which exhibits a high electrical resistance, e.g. at least 10 kohms, preferably at least 100 kohm, more preferably at least 1 Mohm and especially at least 10 Mohms, at low electrical voltages but whose resistance falls from a high value to a low value, e.g. less than 10 ohms, when subjected to a high voltage (the lowest such voltage being referred to as the "threshold voltage)".
  • the device will remain in its low resistance state only for as long as a small "holding" current is maintained through the device, otherwise it will automatically revert to its high resistance state.
  • the threshold foldback device preferably has a capaci ⁇ tance of not more than 100 pF, more preferably not more than 20 pF, and especially not more than 10 pF.
  • Preferred threshold foldback devices include solid state devices such as those based on amorphous chalcogenide compositions, and especially a device based on a composition comprising sele ⁇ nium and/or sulphur together with at least one, and pre ⁇ ferably two of, germanium, gallium, arsenic or antimony.
  • the chalcogenide composition preferably contains not more than 10 atomic %, more preferably not more than 5 atomic % tellurium, and especially contains substantially no tellurium since the presence of significant quantities can lead to an unacceptable reduction in the high resistance (or "off") state resistivity of the composition.
  • Such chalcoge ⁇ nide containing devices have the advantage that they switch extremely rapidly, usually in the region of 1 ns from their high resistance state to their low resistance state when subjected to a voltage transient.
  • chalco ⁇ genide devices usually exhibit very low capacitances, e.g. in the order to 10 pF. Examples of such devices are disclosed in European patent applications Nos.
  • foldback device includes devices referred to as "crowbar” devices. Examples of devices that may be employed in the circuit include Zener diodes, triggered thyristors and the like. The arrangement preferably includes only a single threshold foldback device.
  • the arrangement according to the invention may be employed very effectively to protect the load of an electri ⁇ cal circuit or a component from a voltage transient.
  • the arrangement will usually have a low capacitance, eg. not more than 100 pF, which enables it to be used in very high frequency signal and data transmission systems operating with frequencies of up to about 1 GH Z without adversely affecting the signal or data transmission.
  • the potential difference across both the over- voltage devices increases until it reaches the threshold voltage of the threshold device whereupon the voltage across the load will fall to a low value determined by the "on" state resistance of the threshold foldback device.
  • the threshold foldback device Once the threshold foldback device has switched to its low resistance state the capacitor will begin to charge up with the tran ⁇ sient current and the potential difference across it, and hence across the load, will begin to rise.
  • the threshold foldback device and the additional overvoltage protection device may be separated by a resistor, eg. in the range of up to 1 kohm, or delay so that the voltage across the over ⁇ voltage protection device can continue to increase.
  • a resistor eg. in the range of up to 1 kohm
  • the additional overvoltage protection device will usually be located between the solid-state foldback device and the signal transmission line and be employed to protect the threshold foldback device from the effects of very large transients.
  • a preferred additional overvoltage protection device is a foldback device such as a gas discharge unit or "spark gap". Such devices are capable of transmitting con ⁇ siderable amounts of power and yet have very low capacitan ⁇ ces. If such an additional device is employed it may be separated from the solid-state foldback device by a series resistance of up to 1 kohm which may assist the voltage across the further circuit protection device to rise to the threshold voltage of the device even though the solid-state foldback device has switched to its low resistance state.
  • the capa ⁇ citor can act as a high pass filter and allow the low energy high frequency front edge of the waveform to be handled by the threshold foldback device, and the lower speed high energy portion of the waveform to be handled by the addi ⁇ tional slower overvoltage protection device.
  • Correct choice of the value of the capacitor maintains the threshold fold ⁇ back device in its safe operating area, and ensures that no voltage overshoot occurs because of the lack of speed of operation of the additional overvoltage protection device.
  • the value of the capacitor will depend on a number of fac ⁇ tors including the safe operating area of the foldback device, the source impedance of the circuit and the reliable switching voltage and speed of the further circuit protec ⁇ tion device but will normally be in the range of from 100 pF to 200 nF, preferably from 1 to 100 nF, and especially from 10 to 50 nF.
  • a resettable fuse type device may be included in one of the circuit lines usually between the threshold foldback device (or any other components) and the load.
  • a resettable fuse type device may be included in one of the circuit lines usually between the threshold foldback device (or any other components) and the load.
  • Such a device which will normally exhibit a low resistance but whose resistance will increase to a very high value, is described in our international application No. WO9000817 the disclosure of which is incorporated herein by reference.
  • a voltage clamping device may be employed to limit the voltage overshoot before the threshold switching device has had time to switch.
  • the voltage clamping device may be selected from a number of devices that have voltage limiting properties, for example a back-to-back diode arrangement in which the diodes may comprise semiconductor diodes, avalanche diodes or Zener diodes.
  • the voltage clamping device may comprise a MIM or nin device or a gaseous voltage regulator.
  • MIM and nin devices that may be employed in the invention are described in our International Applications Nos. O9000827 and O9000826 the disclosures of which are incor ⁇ porated herein by reference.
  • the term nin device as used herein includes devices in which the amorphous silicon con ⁇ taining layer is sandwiched between doped layers that can contain either n ⁇ or p ⁇ dopants as described more fully in our copending patent application.
  • the voltage clamping device has a capacitance of not more than 50 pF, and for this reason nin devices are preferred to MIM devi ⁇ ces.
  • the clamping voltage of the device will normally be arranged so that it is above the normal operating voltage of the circuit, e.g. about 1.5 times the normal operating voltage, so that it will not interfere with the operation of the circuit but will not allow too high a voltage across the load before clamping.
  • Yet another device that may be included in a series circuit protection device located between the additional overvoltage protection device and the signal transmission line which will change from a low to a high electrical resistance to shut down the circuit in the case of extremely long duration overloads such as a short circuit etc.
  • a device may, for example, be a PTC (positive temperature coefficient) device circuit protection device as described in US patents Nos. 4,237,441, 4,426,633, 4,426,339 and 4,774,024, and in European application No. 38,713 the disclosures of which are incorporated herein by reference.
  • a suitable device is sold by Raychem Corporation, Menlo Park, California, USA, under the trade mark "Polyswitch" .
  • the arrangement according to the invention may function in a different manner to that described above.
  • the circuit may be subjected to a transient caused by an electrostatic discharge which will normally have a wavefront that rises very rapidly, e.g. at a rate of 1000 V ns _1 or more. It is possible for the solid-state threshold foldback device and any voltage clamping device to be separated by a sufficient delay that the voltage across the foldback device exceeds its threshold voltage before the voltage clamping device experiences the transient to any extent.
  • the transient is shunted across the load by the foldback device without the voltage clamping device or resettable fuse (if present) or the gas discharge tube reacting to it. This is particularly advantageous since it is possible for voltage clamping devices to be permanently damaged by such forms of transient.
  • a pair of transmission lines 1 and 2 connect the signal transmission line (beyond the left side of the drawing) to the load (beyond the right side of the drawing).
  • a solid state threshold foldback device 6 such as an amorphous chalcogenide composition is connected between lines 1 and 2.
  • a 33 nF capacitor 7 is connected in series with the foldback device 6, and a resistance 8, typically of up to 1 kohm, is connected between the lines in series with the foldback device 6 and capacitor 7, the resistance 8 preferably being selected so that, together with all the other series and parallel elements of the arrangement, it matches the incoming line impedance and so minimises the reflected tran ⁇ sient.
  • the resistance is of such a size that not more than 50%, more preferably not more than 25% and espe ⁇ cially not more than 10% of the incident transient power is reflected.
  • a spark gap or discharge tube 9 is connected between the lines 1 and 2 on the transmission line side of the fold ⁇ back device 6.
  • a series resistor 13 is provided between the threshold foldback device 6 and the spark-gap 9 the resistor having a resistance of up to 100 kohms.
  • This simple circuit has the advantage that the threshold foldback device 6, capacitor 7 and any resistances are normally smaller in size than the spark gap 9, and can be physically mounted on the spark gap.
  • the arrange ⁇ ment can be employed in circuits in place of conventional spark gaps often employing the same holder.
  • the arrangement can exhibit very short switching times which are less prone to change with time than with conventional spark gaps.
  • Figure 2 shows a similar circuit protection device as that shown in figure 1, but which is able to protect a cir ⁇ cuit against a wider range of transients.
  • the arrangement includes a solid state threshold foldback device 6, lOOpF to 200 nF capacitor 7, resistance 8 and spark gap 9 which operate as described with reference to figure 1.
  • the arrangement includes a voltage clamping device comprising a pair of back-to-back diodes 4 and 5 connected across the load, and a series resistor 12 of up to 1 kohm between the voltage clamping device 3 and the threshold foldback device 6.
  • a series connected carbon loaded polymer circuit protection device 10 or other overcurrent protection device is included on the transmission line side of the spark gap 9 .
  • a series connected resettable fuse 11 is provided between the voltage clamping device 3 and the load.
  • the voltage across the clamping device 3 rises until the fuse 11 becomes high resistance and device 3 clamps the voltage across it at a substantially constant value, e.g. 5 to 100 V, and usually 10 to 20 V.
  • the voltage across points A and B continues to rise until at typically 80 to 200 V the foldback device 6 changes to its low resistance state.
  • Power is now dissipated in resistor 8 and the voltage across points A and B rises until spark-gap 9 fires, typically at least 20 ns after the start of the transient.
  • the carbon-loaded polymer device 10 will begin to change to its high resistance state and shut the circuit off.

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  • Emergency Protection Circuit Devices (AREA)

Abstract

An arrangement for protecting an electrical circuit from a voltage transient comprises a threshold foldback device (6) arranged to be connected between a pair of current carrying lines of the circuit, and additional overvoltage protection device (9), connected in parallel with the threshold foldback device, and a capacitor (7) having a capacitance in the range of 10 pF to 200 nF connected in series with the threshold foldback device but not with the additional overvoltage device. The additional overvoltage protection device switches more slowly than the threshold foldback device and preferably is a device such as a spark gap or gas discharge tube that exhibits foldback or crowbar characteristics. The arrangement can be employed to protect an electrical circuit or component from a voltage transient and will usually have a low capacitance which enables it to be used in very high frequency systems.

Description

Circuit Protection Arrangement
This invention relates to the protection of electrical circuits from voltage transients.
Voltage transients may be produced in electrical cir¬ cuits by a variety of methods, for example by lightning, electrostatic discharge or by a nuclear electromagnetic pulse. These phenomena may all induce very' large currents on cables and structures such as aircraft and ships which can penetrate and damage electrical systems, either causing hardware damage such as semiconductor burnout or electronic upset such as transmission loss or loss of stored data.
Electrostatic discharges are extremely fast discharges from a capacitor such as a human body. These discharges, because they can be so local, present a great threat to the individual electronic components. Induced electrical tran¬ sients caused by lightning represent a threat to electrical/electronic equipment especially, but not solely, in aerospace vehicles.
The most severe threat to electrical and electronic equipment is the electromagnetic pulse, a typical pulse exhibiting a field strength of about 105 vm"1 with an accom¬ panying H field intensity of 130 Am-1 (based on free space impedance of 377 ohms), a pulse width of a few microseconds and a rise time of a few nanoseconds. In general damaging amplitudes in the pulse occur within the frequency range of 10 kHz to 100 MHz. According to the present invention, there is provided an arrangement for protecting an electrical circuit from a voltage transient, which comprises a threshold foldback device arranged to be connected between a pair of current- carrying lines of the circuit, an additional overvoltage protection device connected in parallel with the threshold foldback device, the additional overvoltage protection device switching more slowly than the threshold switching device, and a capacitor having a capacitance in the range from 100 pF to 200 nF, the capacitor being connected in series with the threshold foldback device but not with the additional overvoltage protection device.
The term "threshold foldback device" as used herein is intended to mean a device which exhibits a high electrical resistance, e.g. at least 10 kohms, preferably at least 100 kohm, more preferably at least 1 Mohm and especially at least 10 Mohms, at low electrical voltages but whose resistance falls from a high value to a low value, e.g. less than 10 ohms, when subjected to a high voltage (the lowest such voltage being referred to as the "threshold voltage)". The device will remain in its low resistance state only for as long as a small "holding" current is maintained through the device, otherwise it will automatically revert to its high resistance state.
The threshold foldback device preferably has a capaci¬ tance of not more than 100 pF, more preferably not more than 20 pF, and especially not more than 10 pF. Preferred threshold foldback devices include solid state devices such as those based on amorphous chalcogenide compositions, and especially a device based on a composition comprising sele¬ nium and/or sulphur together with at least one, and pre¬ ferably two of, germanium, gallium, arsenic or antimony. The chalcogenide composition preferably contains not more than 10 atomic %, more preferably not more than 5 atomic % tellurium, and especially contains substantially no tellurium since the presence of significant quantities can lead to an unacceptable reduction in the high resistance (or "off") state resistivity of the composition. Such chalcoge¬ nide containing devices have the advantage that they switch extremely rapidly, usually in the region of 1 ns from their high resistance state to their low resistance state when subjected to a voltage transient. In addition such chalco¬ genide devices usually exhibit very low capacitances, e.g. in the order to 10 pF. Examples of such devices are disclosed in European patent applications Nos. 196,891, 198,624, 242,902, 261,937, 261,938 and 261,939 (corresponding to US applications Nos. 170,576, 945,640, 214,913, 99,947, 218,511 and 99,931, the disclosures of which are incorporated herein by reference). The term "foldback device" includes devices referred to as "crowbar" devices. Examples of devices that may be employed in the circuit include Zener diodes, triggered thyristors and the like. The arrangement preferably includes only a single threshold foldback device.
The arrangement according to the invention may be employed very effectively to protect the load of an electri¬ cal circuit or a component from a voltage transient. The arrangement will usually have a low capacitance, eg. not more than 100 pF, which enables it to be used in very high frequency signal and data transmission systems operating with frequencies of up to about 1 GHZ without adversely affecting the signal or data transmission.
In most instances, when the circuit is subjected to a transient the potential difference across both the over- voltage devices increases until it reaches the threshold voltage of the threshold device whereupon the voltage across the load will fall to a low value determined by the "on" state resistance of the threshold foldback device. Once the threshold foldback device has switched to its low resistance state the capacitor will begin to charge up with the tran¬ sient current and the potential difference across it, and hence across the load, will begin to rise. The threshold foldback device and the additional overvoltage protection device may be separated by a resistor, eg. in the range of up to 1 kohm, or delay so that the voltage across the over¬ voltage protection device can continue to increase. As the transient continues a point will be reached when sufficient time has elapsed to enable the slower overvoltage protection device to switch to its low resistance state and shunt the transient current across the load.
The additional overvoltage protection device will usually be located between the solid-state foldback device and the signal transmission line and be employed to protect the threshold foldback device from the effects of very large transients. A preferred additional overvoltage protection device is a foldback device such as a gas discharge unit or "spark gap". Such devices are capable of transmitting con¬ siderable amounts of power and yet have very low capacitan¬ ces. If such an additional device is employed it may be separated from the solid-state foldback device by a series resistance of up to 1 kohm which may assist the voltage across the further circuit protection device to rise to the threshold voltage of the device even though the solid-state foldback device has switched to its low resistance state.
In the arrangement according to the invention the capa¬ citor can act as a high pass filter and allow the low energy high frequency front edge of the waveform to be handled by the threshold foldback device, and the lower speed high energy portion of the waveform to be handled by the addi¬ tional slower overvoltage protection device. Correct choice of the value of the capacitor maintains the threshold fold¬ back device in its safe operating area, and ensures that no voltage overshoot occurs because of the lack of speed of operation of the additional overvoltage protection device. The value of the capacitor will depend on a number of fac¬ tors including the safe operating area of the foldback device, the source impedance of the circuit and the reliable switching voltage and speed of the further circuit protec¬ tion device but will normally be in the range of from 100 pF to 200 nF, preferably from 1 to 100 nF, and especially from 10 to 50 nF.
It is possible for additional devices to be included in the arrangement. For example a resettable fuse type device may be included in one of the circuit lines usually between the threshold foldback device (or any other components) and the load. Such a device, which will normally exhibit a low resistance but whose resistance will increase to a very high value, is described in our international application No. WO9000817 the disclosure of which is incorporated herein by reference. A voltage clamping device may be employed to limit the voltage overshoot before the threshold switching device has had time to switch. The voltage clamping device may be selected from a number of devices that have voltage limiting properties, for example a back-to-back diode arrangement in which the diodes may comprise semiconductor diodes, avalanche diodes or Zener diodes. Alternatively the voltage clamping device may comprise a MIM or nin device or a gaseous voltage regulator. MIM and nin devices that may be employed in the invention are described in our International Applications Nos. O9000827 and O9000826 the disclosures of which are incor¬ porated herein by reference. The term nin device as used herein includes devices in which the amorphous silicon con¬ taining layer is sandwiched between doped layers that can contain either n± or p~ dopants as described more fully in our copending patent application. Preferably the voltage clamping device has a capacitance of not more than 50 pF, and for this reason nin devices are preferred to MIM devi¬ ces. The clamping voltage of the device will normally be arranged so that it is above the normal operating voltage of the circuit, e.g. about 1.5 times the normal operating voltage, so that it will not interfere with the operation of the circuit but will not allow too high a voltage across the load before clamping.
Yet another device that may be included in a series circuit protection device located between the additional overvoltage protection device and the signal transmission line which will change from a low to a high electrical resistance to shut down the circuit in the case of extremely long duration overloads such as a short circuit etc. Such a device may, for example, be a PTC (positive temperature coefficient) device circuit protection device as described in US patents Nos. 4,237,441, 4,426,633, 4,426,339 and 4,774,024, and in European application No. 38,713 the disclosures of which are incorporated herein by reference. A suitable device is sold by Raychem Corporation, Menlo Park, California, USA, under the trade mark "Polyswitch" .
In some instances the arrangement according to the invention may function in a different manner to that described above. For example, the circuit may be subjected to a transient caused by an electrostatic discharge which will normally have a wavefront that rises very rapidly, e.g. at a rate of 1000 V ns_1 or more. It is possible for the solid-state threshold foldback device and any voltage clamping device to be separated by a sufficient delay that the voltage across the foldback device exceeds its threshold voltage before the voltage clamping device experiences the transient to any extent. Likewise, where a fast foldback device such as a chalcogenide device is employed, it is possible for the transient to be shunted across the load by the foldback device without the voltage clamping device or resettable fuse (if present) or the gas discharge tube reacting to it. This is particularly advantageous since it is possible for voltage clamping devices to be permanently damaged by such forms of transient.
Two forms of arrangement will now be described by way of example with reference to the accompanying drawings which are circuit diagrams of circuit protection arrangements according to the invention. In the drawings like reference numerals denote the same components.
Referring to figure l of the accompanying drawings, a pair of transmission lines 1 and 2 connect the signal transmission line (beyond the left side of the drawing) to the load (beyond the right side of the drawing). A solid state threshold foldback device 6 such as an amorphous chalcogenide composition is connected between lines 1 and 2. A 33 nF capacitor 7 is connected in series with the foldback device 6, and a resistance 8, typically of up to 1 kohm, is connected between the lines in series with the foldback device 6 and capacitor 7, the resistance 8 preferably being selected so that, together with all the other series and parallel elements of the arrangement, it matches the incoming line impedance and so minimises the reflected tran¬ sient. Preferably the resistance is of such a size that not more than 50%, more preferably not more than 25% and espe¬ cially not more than 10% of the incident transient power is reflected.
A spark gap or discharge tube 9 is connected between the lines 1 and 2 on the transmission line side of the fold¬ back device 6. A series resistor 13 is provided between the threshold foldback device 6 and the spark-gap 9 the resistor having a resistance of up to 100 kohms.
This simple circuit has the advantage that the threshold foldback device 6, capacitor 7 and any resistances are normally smaller in size than the spark gap 9, and can be physically mounted on the spark gap. Thus the arrange¬ ment can be employed in circuits in place of conventional spark gaps often employing the same holder. The arrangement can exhibit very short switching times which are less prone to change with time than with conventional spark gaps. Thus, it is possible to form relatively fast and reliable devices while employing inexpensive GDTs that do not contain tritium.
When the arrangement is subjected to a voltage tran¬ sient, the voltage between the lines rises until at typi¬ cally 80 to 200 V the threshold foldback device 6 changes to its low resistance state. Power is now dissipated in resistance 8 and the voltage across points A and B rises until spark-gap 9 fires, normally at least 20 ns after the start of the transient.
Figure 2 shows a similar circuit protection device as that shown in figure 1, but which is able to protect a cir¬ cuit against a wider range of transients. The arrangement includes a solid state threshold foldback device 6, lOOpF to 200 nF capacitor 7, resistance 8 and spark gap 9 which operate as described with reference to figure 1. In addi- tion the arrangement includes a voltage clamping device comprising a pair of back-to-back diodes 4 and 5 connected across the load, and a series resistor 12 of up to 1 kohm between the voltage clamping device 3 and the threshold foldback device 6.
On the transmission line side of the spark gap 9 a series connected carbon loaded polymer circuit protection device 10 or other overcurrent protection device is included. In addition a series connected resettable fuse 11 is provided between the voltage clamping device 3 and the load.
When the arrangement is subjected to a voltage tran¬ sient the voltage across the clamping device 3 rises until the fuse 11 becomes high resistance and device 3 clamps the voltage across it at a substantially constant value, e.g. 5 to 100 V, and usually 10 to 20 V. The voltage across points A and B continues to rise until at typically 80 to 200 V the foldback device 6 changes to its low resistance state. Power is now dissipated in resistor 8 and the voltage across points A and B rises until spark-gap 9 fires, typically at least 20 ns after the start of the transient.
If the duration of the transient exceeds about 100 s, the carbon-loaded polymer device 10 will begin to change to its high resistance state and shut the circuit off.

Claims

CLAIMS :
1. An arrangement for protecting an electrical circuit from a voltage transient, which comprises a threshold fold¬ back device arranged to be connected between a pair of current-carrying lines of the circuit, an additional over¬ voltage protection device connected in parallel with the threshold foldback device, the additional overvoltage pro¬ tection device switching more slowly than the threshold switching device, and a capacitor having a capacitance in the range of from 100 pF to 200 nF, the capacitor being con¬ nected in series with the threshold foldback device but not with the additional overvoltage protection device.
2. An arrangement as claimed in claim 1, which includes a voltage clamping device in parallel with the threshold fold¬ back device and the overvoltage protection device.
3. An arrangement as claimed in claim 1 or claim 2, which includes a resistance of such a size that the total of all series and parallel elements matches the incoming line impe¬ dance.
4. An arrangement as claimed in any one of claims l to 3, wherein the overvoltage protection device is a foldback device.
5. An arrangement as claimed in any one of claims 1 to 4, wherein the overvoltage protection device is capable of shunting a larger amount of energy across a load connected to the pair of lines than is the threshold foldback device.
6. An arrangement as claimed in claim 4 wherein the addi¬ tional circuit protection device comprises a spark-gap or a gas discharge tube.
7. An arrangement as claimed in any one of claims 1 to 6, wherein the threshold foldback device includes a switching element that is formed from an amorphous chalcogenide com¬ position.
8. An arrangement as claimed in claim 7, wherein the chalcogenide composition comprises selenium and/or sulphur together with at least one of germanium, gallium, arsenic or antimony, but contains no more than 10 atomic % tellerium.
9. An arrangement as claimed in any one of claims 1 to 8, wherein the theshold foldback device has a resistance in its high resistance state of at least 1 M ohm.
10. An arrangement as claimed in any one of claims 1 to 9, wherein the threshold foldback device has a capacitance of not more than 100, preferably not more than 50 pF.
11. An arrangement as claimed in claim 10, wherein the capacitance of the threshold foldback device is not more than 20 pF.
12. An arrangement as claimed in any one of claims 1 to 11, wherein the circuit at least partly absorbs internally generated switching transients.
* * * * * *
PCT/GB1991/000120 1990-01-30 1991-01-29 Circuit protection arrangement WO1991011840A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB909002094A GB9002094D0 (en) 1990-01-30 1990-01-30 Circuit protection arrangement
GB9002094.2 1990-01-30

Publications (1)

Publication Number Publication Date
WO1991011840A1 true WO1991011840A1 (en) 1991-08-08

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AU (1) AU7186991A (en)
GB (1) GB9002094D0 (en)
WO (1) WO1991011840A1 (en)

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CN104134988A (en) * 2014-08-21 2014-11-05 国家电网公司 Multifunctional lightning protection device of intelligent single-phase electric meter

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CN1043499C (en) * 1995-11-17 1999-05-26 李长益 Low-voltage distribution type lightning-protection module
JP3854305B1 (en) * 2005-12-09 2006-12-06 均 木嶋 Overvoltage protector, overvoltage protection method
CN101350516B (en) * 2007-07-16 2011-11-30 台达电子工业股份有限公司 Circuit and method for protecting energy storage apparatus
CN102185304A (en) * 2011-05-16 2011-09-14 浙江大华技术股份有限公司 Surge protection circuit of video input signal

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US3973224A (en) * 1975-10-28 1976-08-03 The United States Of America As Represented By The Secretary Of The Army Tandem configuration for EMP protection
US4616286A (en) * 1982-08-02 1986-10-07 Puroflow Corporation Power line filter
EP0259178A2 (en) * 1986-09-05 1988-03-09 Raychem Limited Circuit protection arrangement
WO1990000826A1 (en) * 1988-07-13 1990-01-25 Raychem Limited Circuit protection arrangement
WO1990003681A1 (en) * 1988-09-20 1990-04-05 Raychem Limited Circuit protection arrangement

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1126672A2 (en) * 2000-02-18 2001-08-22 Telefonica, S.A. Protection equipment for pulse code modulation installations
EP1126672A3 (en) * 2000-02-18 2004-07-14 Telefonica, S.A. Protection equipment for pulse code modulation installations
CN104134988A (en) * 2014-08-21 2014-11-05 国家电网公司 Multifunctional lightning protection device of intelligent single-phase electric meter

Also Published As

Publication number Publication date
AU7186991A (en) 1991-08-21
GB9002094D0 (en) 1990-03-28
CN1053868A (en) 1991-08-14

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