Integrated thermally protected varistor and discharge tube

Abstract

An integrated component for protecting against temporary power surges comprises a first conductive lead and a second conductive lead, each of which mounted on an electrical circuit; a gas discharge tube; a thermally protected varistor and a thermal fuse. The thermally protected varistor comprises a varistor body, a first varistor electrode and a second varistor electrode that are positioned on either side of the varistor body. The varistor body rises in temperature when the voltage imposed between the first and the second varistor electrodes exceeds a voltage threshold. An electrical connection is made via the thermal fuse.

Claims

1. An integrated component for protecting against temporary power surges, comprising: a first conductive lead and a second conductive lead, each conductive lead mounted to an electrical circuit; a gas discharge tube comprising a first discharge tube electrode, a second discharge tube electrode and a discharge tube body arranged between the first and the second discharge tube electrodes, wherein the body of the discharge tube rises in temperature when an electric current flows through it; a thermal fuse comprising with a temperature-sensitive element to provide an electrical connection in an initial state and to interrupt said electrical connection when subjected to a temperature greater than a temperature threshold; and a varistor comprising: a varistor body, and a first varistor electrode and a second varistor electrode positioned on either side of the varistor body, wherein the varistor body rises in temperature when the voltage applied across the first and the second varistor electrodes exceeds a voltage threshold; wherein the first conductive lead is connected to the first varistor electrode by a first connection, the second varistor electrode is connected to the first discharge tube electrode by a second connection, the second discharge tube electrode being connected to the second conductive lead by a third connection, and the first connection is made through the thermal fuse, wherein the temperature-sensitive element is sensitive to a temperature increase of at least one of the discharge tube and the varistor, wherein the temperature-sensitive element of the thermal fuse is a metal connector having a melting point equal to or less than a thermal safety temperature threshold for the varistor, wherein a first end of the metal connector is soldered to the first varistor electrode, the component furthermore comprising an insulator arranged on a surface of the first varistor electrode such that a second end of the metal connector does not make contact with the surface of the first varistor electrode.

2. The integrated component according to claim 1, wherein the metal connector melts upon a temperature increase above the melting point of the metal connector; and wherein a portion of the first varistor electrode is covered by a thermoactive material, wherein the thermoactive material melts upon a temperature increase below the melting point of the metal connector, and increases the coefficient of spreading of the metal connector in the liquid state over the first electrode of the varistor, such that the metal connector transforms into a metal film spreading over the first electrode of the varistor upon a temperature increase above the melting point of the metal connector.

3. The integrated component according to claim 1, wherein the insulator is a plate made of plastic, ceramic or glass.

4. The integrated component according to claim 2, wherein the insulator is a plate made of plastic, ceramic or glass.

5. The integrated component according to claim 1, furthermore comprising a coating comprising a protective resin, the coating being arranged around the varistor, the thermal fuse and the discharge tube so as to form an electrically insulating protective barrier, wherein only a portion of each of the two conductive leads protruding beyond the coating.

6. The integrated component according to claim 2, furthermore comprising a coating comprising a protective resin, the coating being arranged around the varistor, the thermal fuse and the discharge tube so as to form an electrically insulating protective barrier, wherein only a portion of each of the two conductive leads protruding beyond the coating.

7. The integrated component according to claim 3, furthermore comprising a coating comprising a protective resin, the coating being arranged around the varistor, the thermal fuse and the discharge tube so as to form an electrically insulating protective barrier, wherein only a portion of each of the two conductive leads protruding beyond the coating.

8. The integrated component according to claim 5, wherein the protective resin comprises an epoxy resin.

9. A method for manufacturing an integrated component for protecting against temporary power surges, comprising: providing a first and a second conductive lead for mounting on an electrical circuit; providing a gas discharge tube comprising a first discharge tube electrode, a second discharge tube electrode and a discharge tube body arranged between the first and the second discharge tube electrodes, wherein the body of the discharge tube rises in temperature when an electric current flows through it; providing a thermal fuse equipped with a temperature-sensitive element designed to provide an electrical connection in an initial state and to interrupt said electrical connection when it is subjected to a temperature greater than a threshold; providing a varistor comprising: a varistor body, and a first varistor electrode and a second varistor electrode that are positioned on either side of the varistor body, the varistor body being able to rise in temperature when the voltage applied across the first and the second varistor electrodes exceeds a voltage threshold; making a first electrical connection between the first conductive lead and the first varistor electrode, making a second electrical connection between the first discharge tube electrode and the second varistor electrode, and making a third electrical connection between the second discharge tube electrode and the second conductive lead, wherein the first electrical connection is made via the thermal fuse, wherein the temperature-sensitive element of the thermal fuse is a metal connector having a melting point equal to or less than a thermal safety temperature threshold for the varistor, soldering a first end of the metal connector to the first varistor electrode, and arranging an insulator on a surface of the first varistor electrode such that a second end of the metal connector does not make contact with the surface of the first varistor electrode.

10. An integrated component for protecting against temporary power surges, comprising: a first conductive lead and a second conductive lead, each conductive lead mounted to an electrical circuit; a gas discharge tube comprising a first discharge tube electrode, a second discharge tube electrode and a discharge tube body arranged between the first and the second discharge tube electrodes, wherein the body of the discharge tube rises in temperature when an electric current flows through it; a thermal fuse comprising with a temperature-sensitive element to provide an electrical connection in an initial state and to interrupt said electrical connection when subjected to a temperature greater than a temperature threshold; and a varistor comprising: a varistor body, and a first varistor electrode and a second varistor electrode positioned on either side of the varistor body, wherein the varistor body rises in temperature when the voltage applied across the first and the second varistor electrodes exceeds a voltage threshold; wherein the first conductive lead is connected to the first varistor electrode by a first connection, the second varistor electrode is connected to the first discharge tube electrode by a second connection, the second discharge tube electrode being connected to the second conductive lead by a third connection, and the second connection is made through the thermal fuse, wherein the temperature-sensitive element is sensitive to a temperature increase of at least one of the discharge tube and the varistor, wherein the temperature-sensitive element of the thermal fuse is a metal connector having a melting point equal to or less than a thermal safety temperature threshold for the varistor, wherein a first end of the metal connector is soldered to the second varistor electrode, the component furthermore comprising an insulator arranged on a surface of the second varistor electrode such that a second end of the metal connector does not make contact with the surface of the second varistor electrode.

11. The integrated component according to claim 10, wherein the metal connector melts upon a temperature increase above the melting point of the metal connector; and wherein a portion of the second varistor electrode is covered by a thermoactive material, wherein the thermoactive material melts upon a temperature increase below the melting point of the metal connector, and increases the coefficient of spreading of the metal connector in the liquid state over the second electrode of the varistor, such that the metal connector transforms into a metal film spreading over the second electrode of the varistor upon a temperature increase above the melting point of the metal connector.

12. The integrated component according to claim 10, furthermore comprising a coating comprising a protective resin, the coating being arranged around the varistor, the thermal fuse and the discharge tube so as to form an electrically insulating protective barrier, wherein only a portion of each of the two conductive leads protruding beyond the coating.

13. The integrated component according to claim 12, wherein the protective resin comprises an epoxy resin.

14. A method for manufacturing an integrated component for protecting against temporary power surges, comprising: providing a first and a second conductive lead for mounting on an electrical circuit; providing a gas discharge tube comprising a first discharge tube electrode, a second discharge tube electrode and a discharge tube body arranged between the first and the second discharge tube electrodes, wherein the body of the discharge tube rises in temperature when an electric current flows through it; providing a thermal fuse equipped with a temperature-sensitive element designed to provide an electrical connection in an initial state and to interrupt said electrical connection when it is subjected to a temperature greater than a threshold; providing a varistor comprising: a varistor body, and a first varistor electrode and a second varistor electrode that are positioned on either side of the varistor body, the varistor body being able to rise in temperature when the voltage applied across the first and the second varistor electrodes exceeds a voltage threshold; making a first electrical connection between the first conductive lead and the first varistor electrode, making a second electrical connection between the first discharge tube electrode and the second varistor electrode, and making a third electrical connection between the second discharge tube electrode and the second conductive lead, wherein the second electrical connection is made via the thermal fuse, wherein the temperature-sensitive element of the thermal fuse is a metal connector having a melting point equal to or less than a thermal safety temperature threshold for the varistor, soldering a first end of the metal connector to the second varistor electrode, and arranging an insulator on a surface of the second varistor electrode such that a second end of the metal connector does not make contact with the surface of the second varistor electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other aims, details, features and advantages thereof will become more clearly apparent over the course of the following description of several particular embodiments of the invention, which are given solely by way of non-limiting illustration, with reference to the appended drawings.

(2) In the drawings:

(3) FIG. 1 is a front view of a component according to a first embodiment, when it is not coated.

(4) FIG. 2 is a rear view of the component of FIG. 1.

(5) FIG. 3 is a side view of the component of FIG. 1.

(6) FIG. 4 is a circuit diagram of the component of FIG. 1.

(7) FIG. 5 is a perspective view of the component of FIG. 1, when it is coated.

(8) FIG. 6 is a front view of a component according to a second embodiment, when it is not coated.

(9) FIG. 7 is a side view of the component of FIG. 6.

(10) FIG. 8 is a circuit diagram of the component of FIG. 6.

(11) FIG. 9 is a perspective view of the component of FIG. 6, when it is coated.

(12) FIG. 10 is a circuit diagram of a third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(13) A discrete component for mounting on a printed electrical circuit and to protect an electrical device against power surges will now be described with reference to the accompanying figures.

(14) Three alternative embodiments of such a discrete component will be described. The first embodiment is described with reference to FIGS. 1 to 5. The second embodiment is described with reference to FIGS. 6 to 9. The third embodiment is described with reference to FIG. 10. Identical or similar elements have been referenced with the same reference numbers in the figures showing the two embodiments.

(15) FIG. 4 shows a circuit diagram for component 1 as shown in FIG. 1 according to the first embodiment. The circuit comprises a discharge tube 4, a varistor 2 and a thermal fuse 3 mounted in series between two electrical lines 5 and 6 of a circuit or electrical device to be protected. The electrical lines 5 and 6 may be any conductor used to supply electrical power at a low or medium voltage to an electrical device. The thermal fuse 3 is connected to the electrical line 5 and to the varistor 2. A thermal bridge 7 makes it possible to spread the heat emitted by the varistor 2 to the thermal fuse 3.

(16) The discharge tube 4 is connected to the varistor 2 and to the electrical line 6 to be protected.

(17) The discrete component 1 comprises the following three functions: a discharge tube 4, a varistor 2 and a thermal fuse 3. The component and a method for manufacturing the component according to the first embodiment, will be described with reference to FIGS. 1, 2, 3 and 5.

(18) The discrete component 1 comprises a varistor 2, for example a varistor of rectangular shape, comprising a rectangular zinc oxide wafer 9 and two electrodes 10 and 11, which are also rectangular and positioned on either side of the zinc oxide wafer 9.

(19) The component also comprises a gas discharge tube 4 having two electrodes. The gas discharge tube 4 is preferably small. For example a BB series 2-electrode gas discharge tube, a BH series 2-electrode gas discharge tube, or a BG series gas-filled spark gap gas discharge tube such as the BG600, available from CITEL at http://www.citel.fr/en/produit/citel-gas-discharge-tubes-range.html may be used for the invention.

(20) The component 1 also comprises an insulating wafer 14, for example made of plastic, having dimensions considerably smaller than the dimensions of the electrode 10, for example a tenth of the rectangular area of the electrode 10.

(21) The component 1 also comprises a heat-fusible electrically conductive bar 13, preferably made of metal, for example of tin.

(22) The component 1 also comprises two electrical tabs 15 and 16.

(23) The manufacture of such a component 1 is susceptible to mass production.

(24) The manufacture of such a component 1 comprises in particular the step of soldering one of the ends of the heat-fusible bar 13 to the electrode 10 via a solder joint 8 formed with the material of the heat-fusible bar 13.

(25) One face of the insulating wafer 14 is then positioned on the electrode 10. A step of bonding the face of the insulating wafer 14 to the electrode 10 may optionally be provided.

(26) The manufacturing also comprises a step of fastening the other end of the heat-fusible bar 13 to the other face of the insulating wafer 14, such that the heat-fusible bar is in electrical contact with the varistor only via the end soldered to the electrode 10.

(27) The manufacturing further comprises a step of soldering joint 18 between a first discharge tube electrode and the electrode 11, and another of soldering joint 17 between tab 15 and the end of the heat-fusible bar 13 placed on the insulating wafer 14.

(28) A further step comprises soldering joint 19 between tab 16 and a second discharge tube electrode.

(29) The manufacture of the component then comprises a step of providing a thermoactive material 21 in an area of the surface of the electrode 10.

(30) The thermoactive material 21 is heat-fusible and has aggressive chemical properties, such that it cleans and purifies impurities from the surface onto which it melts.

(31) The thermoactive material is for example a material selected from the following materials: A no clean (NC) flux, composed of resin, solvent and a small amount of activator. A flux of this type is not conductive. A water soluble (WS) flux, composed of organic acids, thixotropes and solvents. A rosin mildly activated (RMA) flux, composed of resin, solvent and a small amount of activator. A flux of this type is not conductive. A rosin activated (RA) flux, composed of resin, solvent and aggressive activators.

(32) Finally, in order to protect the component 1 thus obtained, it is advantageous to cover the varistor 2, the discharge tube 4 and the heat-fusible bar 13 with a resin coating 20 (see FIG. 5), such that only one end of each of the tabs 15, 16 intended to be mounted on a printed circuit, protrude beyond the coating 20.

(33) The operation of such a component during a temporary power surge, for example caused by lightning, between the lines 5 and 6 will be described. The power surge triggers the discharge tube 4. Specifically, the discharge tube 4 changes from a very high impedance state to a quasi-short circuit upon the application of a voltage greater than a voltage threshold across the electrical line 5 and the electrical line 6.

(34) Moreover, this power surge induces a current that flows through the varistor. The current flowing through the varistor 2 then induces gradual heating of the varistor 2 and therefore heating of the thermal fuse 3 by way of the thermal bridge 7 between the varistor and the thermal fuse 3. When the power surge exceeds the nominal voltage threshold of the varistor 2, the varistor 2 changes to low impedance and limits the voltage across its terminals. The discrete component is therefore readily able to protect the electrical line 5 from the applied power surge.

(35) However, beyond a heating threshold corresponding to a disconnection temperature of the thermal fuse 3, the induced current is abruptly interrupted by the thermal fuse 3.

(36) The thermal fuse 3 comprises the heat-fusible bar 13 and also the thermoactive material 21.

(37) The disconnection enabled by the heat-fusible bar 13 and the thermoactive material 21 will now be described in more detail.

(38) The heating induced on the thermoactive material 21 results in the material melting and flowing onto the surface of the first electrode 10, so as to clean and purify the surface of the first electrode 10.

(39) The heating induced on the heat-fusible bar 13 by the thermal bridge 7 will also cause the heat-fusible bar 13 to melt, subsequent to the melting of the thermoactive material 21, the melting point of which is lower. The molten material of the bar then forms a drop that slides and spreads over the surface of the first electrode 10. Specifically, the cleaning produced by the molten thermoactive material 21 on the surface of the first varistor electrode 10 causes the wettability of tin on the surface of the first varistor electrode 10 to increase. As a result, the molten tin of the heat-fusible bar 13 forms a thin metal film over the entire surface of the first varistor electrode 10. This thin film is not able to provide the electrical connection between the first varistor electrode and the first conductive lead 15.

(40) The magnitude of the current therefore becomes zero.

(41) The component 1 is thus able to protect the electrical line 5 from fires by completely disconnecting it upon a temperature increase beyond a temperature threshold.

(42) With reference to FIGS. 6 to 9, a second embodiment of the discrete component 1 according to the invention will be disclosed. Elements like or similar to those of the figures of the first embodiment have been identified by the same reference numbers.

(43) FIG. 8 shows an equivalent circuit diagram of the component 1 of FIG. 6 according to the second embodiment. As in the first embodiment, the circuit comprises a discharge tube 4, a varistor 2 and a thermal fuse 3 mounted in series on an electrical line to be protected. In contrast to the first embodiment, the thermal fuse 3 is arranged between the varistor 2 and the discharge tube 4.

(44) The varistor 2 is connected to the electrical line 5 to be protected and to the thermal fuse 3. A thermal bridge 7 makes it possible to diffuse the heat emitted by the varistor 2 and the discharge tube 4 to the thermal fuse 3. The discharge tube 4 is connected to the thermal fuse 3 and to a second electrical line 6 to be protected.

(45) A method for manufacturing the discrete component according to the second embodiment, incorporating the three following functions: discharge tube 4, varistor 2 and thermal fuse 3, will be described with reference to FIGS. 6 to 9. The discrete component 1 according to this second embodiment comprises the same elements as the component according to the first embodiment. Only the manufacturing method differs for some steps.

(46) The manufacture of the component 1 comprises in particular the step of soldering one of the ends of the heat-fusible bar 13 to the electrode 11 via a solder joint 8.

(47) In this second embodiment, one face of the insulating wafer 14 is placed on the electrode 11, and not on the electrode 10. Advantageously, this face of the insulating wafer 14 is able to be bonded to the electrode 11.

(48) In addition, it is necessary to fasten the other end of the heat-fusible bar 13 to the other face of the insulating wafer 14, such that the heat-fusible bar is in electrical contact with the varistor only through its end soldered to the electrode 11, and not to the electrode 10.

(49) It is also necessary to produce a solder joint 18 between a first discharge tube electrode and the end of the heat-fusible bar 13 placed on the insulating wafer 14.

(50) The electrical tabs are also soldered differently than in the first embodiment. Specifically, the manufacturing comprises producing a solder joint 17 between the tab 15 and the electrode 10, and producing a solder joint 19 between the tab 16 and a second discharge tube electrode.

(51) A third embodiment is shown in FIG. 10. FIG. 10 shows a circuit diagram for the component 1 according to the third embodiment. As in the first embodiment, the circuit comprises a discharge tube 4, a varistor 2 and a thermal fuse 3 mounted in series on an electrical line to be protected. In contrast to the first embodiment, the discharge tube 4 is arranged between the thermal fuse 3 and the varistor 2. In such an embodiment, the thermal fuse 3 is thus sensitive only to heating by the discharge tube 4 by way of bridge 7.

(52) Although the invention has been described in connection with several particular embodiments, it is readily obvious that it is in no way limited thereto, and that it comprises all of the technical equivalents of the means described, and also combinations thereof if these fall within the scope of the invention. For example, it is possible to provide other varistors for manufacturing the component. For example, the varistor used may have technical features different from those outlined above, for example dimensions of about 3434 mm in width and in length, a maximum nominal operating voltage of about 385 volts AC and about 505 volts DC, a DC voltage at a current of 1 mA of between about 590 and 600 volts, and a maximum discharge current of 40 kA (8/20 s).

(53) The use of the verb have, comprise or include, and of its conjugated forms, does not exclude elements or steps other than those mentioned in a claim from being present. The use of the indefinite article a or an for an element or a step does not exclude a plurality of such elements or steps from being present, unless indicated otherwise.

(54) In the claims, any reference sign between parentheses should not be interpreted as a limitation of the claim.