Patent Description:
The present invention relates to the field of circuit protection, and in particular, to an overheat protection device and a varistor. <CIT> discloses an overheat protection device according to the preamble of claim <NUM>.

A varistor is a resistor device provided with nonlinear volt-ampere characteristics, and is mainly used for performing voltage clamping when a circuit is subjected to overvoltage and absorbing redundant current so as to protect a sensitive device. A varistor is equivalent to a variable resistor connected in parallel in the circuit. When the circuit is in normal use, the varistor has a high impedance and small leakage current, and can be regarded as an open circuit having little effect on the circuit. However, when very high surge voltage occurs, the resistance of the varistor drops instantaneously (the resistance may change from the megaohm level to the milliohm level), causing it to allow a large current to flow through while clamping the overvoltage at a certain value.

A thermally protected varistor is a product capable of providing instant heat removal. This property is achieved by an alloy type thermal fuse and a varistor through an internal effective thermocouple and the structure thereof. A thermally protected varistor has multiple protective functions for overvoltage, overcurrent, and overtemperature. The varistor is promptly removed from the circuit by fusing the alloy in an overvoltage, overcurrent, or overtemperature, thus preventing fires caused by the varistor being continuously overheated.

However, in the above structure, when the alloy of the fuse is fused, no effective physical isolation structure between the fused alloy material and electrodes of the varistor exists. The varistor may still be connected to the circuit, and the varistor may catch on fire from being overheated continuously, thus posing a certain potential for safety hazards.

In order to solve at least one aspect of the above problems, an overheat protection device and a varistor are defined in claims <NUM> and <NUM> respectively.

An overheat protection device is provided in an embodiment of the present disclosure, including: a first electrode and a second electrode disposed to be spaced apart; a hot-melt wire located between the first electrode and the second electrode, the hot-melt wire being in electrical contact with the first electrode and the second electrode; and an insulator supporting the first electrode and the second electrode, wherein the hot-melt wire is melted into a liquid hotmelt material when the ambient temperature reaches a predetermined temperature, the liquid hotmelt material wets the first electrode and the second electrode, and the liquid hot-melt material does not wet the insulator at least at a portion located between the first electrode and the second electrode.

In some embodiments, the insulator comprises a plate-shaped or corrugated structure, and the first electrode, the second electrode, and the hot-melt wire are disposed on one side of the plate-shaped or corrugated structure.

In some embodiments, the overheat protection device further comprises: a protective layer, wherein the protective layer and the plate-shaped or corrugated structure enclose a cavity; at least a portion of the first electrode, at least a portion of the second electrode, and the hot-melt wire are accommodated in the cavity.

In some embodiments, the liquid hot-melt material does not wet the protective layer.

In some embodiments, the overheat protection device further comprises at least one wetting component, the one wetting component is disposed between the first electrode and the second electrode, the first electrode, the at least one wetting component, and the second electrode are successively and sequentially arranged to be spaced apart in an extension direction of the hotmelt wire, and the liquid hot-melt material wets the wetting component.

The insulator comprises a cylindrical structure, and the first electrode, the second electrode, and the hot-melt wire are disposed in the cylindrical structure.

In some embodiments, at least one of the first electrode and the second electrode is a layered electrode, a columnar electrode, or a sponge electrode.

A varistor is provided in an embodiment of the present disclosure, the varistor comprising: a varistor body; and the overheat protection device disposed on the pressure-sensitive electronic body as described according to the above embodiments, wherein compared with the first electrode and the second electrode, the insulator is closer to the varistor body.

In some embodiments, the varistor body comprises a first electrode layer, a varistor chip, and a second electrode layer disposed sequentially to be stacked, and the second electrode layer and the insulator are disposed to face each other.

In some embodiments, the varistor comprises a heat conductive layer, and the heat conductive layer is disposed between the insulator and the second electrode layer.

In some embodiments, the second electrode layer is electrically connected to one of the first electrode and the second electrode, and the varistor further comprises: a first pin, the first pin being electrically connected to the first electrode layer; and a second pin, the second pin being electrically connected to the other one of the first electrode and the second electrode.

In some embodiments, the varistor further comprises an encapsulation layer, the encapsulation layer cladding the varistor body and the overheat protection device.

From the description of the present invention in the following and with reference to accompanying drawings, other objectives and advantages of the present invention will become apparent and can help one understand the present invention thoroughly.

The technical solutions of the present invention will be further described specifically below through embodiments with reference to the accompanying drawings. In the description, the same or similar reference numerals indicate the same or similar members. The description of implementation manners of the present invention below with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention, and should not be construed as limitations to the present invention.

In addition, in order to provide a clear explanation and a thorough understanding of the embodiments of the present disclosure, numerous specific details are set forth in the following detailed description. However, it is obvious that one or a plurality of embodiments can still be implemented without these specific details.

It should be noted that "on," "formed on," and "disposed on" as described herein may indicate that one layer is formed or disposed on another layer directly, and may also indicate that one layer is formed or disposed on another layer indirectly, i.e., another layer exists between the two layers.

It should be noted that terms such as "first" and "second" may be used herein for describing various members, components, elements, regions, layers, and/or portions; however, these members, components, elements, regions, layers and/or portions should not be limited by these terms. Instead, these terms are used for distinguishing one member, component, element, region, layer and/or portion from another. Therefore, for example, a first member, a first component, a first element, a first region, a first layer, and/or a first portion discussed below may be referred to as a second member, a second component, a second element, a second region, a second layer and/or a second portion.

An overheat protection device is provided in the present disclosure. The overheat protection device includes a first electrode and a second electrode disposed to be spaced apart; a hot-melt wire located between the first electrode and the second electrode; a first end of the hotmelt wire being in electrical contact with the first electrode; and a second end of the hot-melt wire being in electrical contact with the second electrode; and an insulator supporting the first electrode and the second electrode. The hot-melt wire is melted into a liquid hot-melt material when the ambient temperature reaches a predetermined temperature; the liquid hot-melt material wets the first electrode and the second electrode, and the liquid hot-melt material does not wet the insulator at least at a portion located between the first electrode and the second electrode.

Regarding the overheat protection device provided by the present disclosure, the materials of the first electrode, the second electrode, and the insulator are selected such that the liquid hot-melt material wets the first electrode and the second electrode and does not wet at least a portion of the insulator. As a result, when the hot-melt wire is melted when the ambient temperature reaches the predetermined temperature, the liquid hot-melt material is collected at the first electrode and the second electrode that are spaced apart from each other, so that the first electrode and the second electrode are completely insulated, thereby ensuring that the thermal protection device is in a complete open-circuit state.

Specifically, an overheat protection device <NUM> is provided in an embodiment of the present disclosure. <FIG> is a schematic structural plan view according to the overheat protection device <NUM>. <FIG> is a schematic cross-sectional structural view of <FIG> taken along the line aa. As shown in <FIG>, the overheat protection device <NUM> includes an insulator <NUM>, a first electrode <NUM> and a second electrode <NUM> located on the insulator <NUM>, and a hotmelt wire <NUM> electrically connecting the first electrode <NUM> and the second electrode <NUM>. In this embodiment, the insulator is of a plate-shaped or corrugated structure (an example of a plate-shaped structure is shown in <FIG>). The first electrode <NUM> and the second electrode <NUM> are located on one side of the insulator <NUM> and are disposed to be spaced apart from each other. Two ends of the hot-melt wire <NUM> are in electrical contact with the first electrode <NUM> and the second electrode <NUM>, respectively. For example, the two ends of the hot-melt wire <NUM> are soldered to the first electrode <NUM> and the second electrode <NUM>, respectively.

The hot-melt wire <NUM> can be made of a conductive material having a lower melting point, such as tin, aluminum-antimony alloy, tin-bismuth alloy, tin-copper alloy, and tin-silver-copper alloy. Thus, when the ambient temperature reaches the predetermined temperature, the hot-melt wire <NUM> is melted and broken, so that the electrical connection between the first electrode <NUM> and the second electrode <NUM> of the overheat protection device <NUM> is broken, and the overheat protection device <NUM> is in an open-circuit state.

The insulator <NUM> of the plate-shaped or corrugated structure can be made of a material such as ceramic, glass, alumina, SiN, and polyimide (PI) to ensure that the liquid hot-melt material does not wet the insulator <NUM>. The first electrode <NUM> and the second electrode <NUM> have melting points higher than the melting point of the hot-melt wire <NUM>, and can be made of a material such as Cu, Ag, Au, Ni, and Pd, to ensure that the liquid hot-melt material wets the first electrode <NUM> and the second electrode <NUM> of the insulator. Therefore, when the hot-melt wire <NUM> is melted when the ambient temperature reaches the predetermined temperature, the liquid hot-melt material flows under the action of surface tension of the liquid hot-melt material, and is collected at the first electrode <NUM> and the second electrode <NUM> that are spaced apart from each other. Substantially no liquid hot-melt material is present on the surface of the insulator <NUM> between the first electrode <NUM> and the second electrode <NUM>. As shown in <FIG>, the liquid hot-melt material flows to and is collected at the first electrode <NUM> and the second electrode <NUM>, and covers the first electrode <NUM> and the second electrode <NUM>. As a result, the first electrode <NUM> and the second electrode <NUM> are completely insulated, thereby ensuring that the thermal protection device <NUM> is in a complete open-circuit state.

In this embodiment, the first electrode <NUM> and the second electrode <NUM> each have a layered structure. For example, the first electrode <NUM> and the second electrode <NUM> may be copper pads disposed on one side of the insulator <NUM> and spaced apart from each other.

In some embodiments, it is also possible to provide an arrangement in which only a portion of the insulator <NUM> located between the first electrode <NUM> and the second electrode <NUM> is not wet by the liquid hot-melt material.

In some embodiments, the overheat protection device <NUM> may further include a protective layer <NUM> to avoid external interference with the fluidity of the liquid hot-melt material and to ensure the flow of the liquid hot-melt material under surface tension, as shown in <FIG> (the protective layer is not shown in <FIG>). The protective layer <NUM> and the insulator <NUM> having a plate-shaped or corrugated structure enclose a cavity, and at least a portion of the first electrode <NUM>, at least a portion of the second electrode <NUM>, and the hot-melt wire <NUM> are accommodated in the cavity. The protective layer <NUM> can be made of a material such as SiN and polyimide (PI), and the liquid hot-melt material does not wet the protective layer <NUM>. Therefore, the liquid hot-melt material formed by melting the hot-melt wire <NUM> can be collected at the first electrode <NUM> and the second electrode <NUM> in the cavity under the action of surface tension. The protective layer <NUM> thus ensures that the fluidity of the liquid hot-melt material is not interfered by external factors.

In some embodiments, the distance between the first electrode and the second electrode <NUM> is, for example, greater than or equal to <NUM>, ensuring that the liquid hot-melt materials respectively collected at the first electrode <NUM> and the second electrode <NUM> are sufficiently separated.

<FIG> is a schematic structural plan view of an overheat protection device according to another embodiment of the present disclosure, which differs from the overheat protection device shown in <FIG> in that the overheat protection device <NUM> further includes at least one wetting component <NUM>, for example, two wetting components. The wetting component <NUM> is also disposed on the insulator <NUM> and located between the first electrode <NUM> and the second electrode <NUM>. The first electrode <NUM>, the second electrode <NUM>, and the wetting component <NUM> are disposed to be spaced apart from each other. For example, as shown in <FIG>, the first electrode <NUM>, the second electrode <NUM>, and the wetting component <NUM> each have an elongated shape and collectively form a zebra crossing shape. The wetting component <NUM> can be made of a material such as Cu, Ag, Au, Ni, and Pd, such that the liquid hot-melt material wets the wetting component <NUM>. When the hot-melt wire <NUM> is melted into the liquid hot-melt material when the ambient temperature reaches the predetermined temperature, the liquid hot-melt material is collected at the first electrode <NUM>, the second electrode <NUM>, and the wetting component <NUM> that are spaced apart from each other, and the liquid hot-melt material is divided into a plurality of portions disconnected to each other, so that the first electrode <NUM> and the second electrode <NUM> are completely insulated, thereby ensuring that the thermal protection device <NUM> is in a complete open-circuit state. The overheat protection device in this embodiment can be used in a case where the amount of the liquid hot-melt material melted from the hot-melt wire <NUM> is comparatively large.

In some embodiments, the wetting component <NUM> can be made of the same material as the first electrode <NUM> and the second electrode <NUM>. In this case, the wetting component <NUM> can be formed on the insulator <NUM> simultaneously with the first electrode <NUM> and the second electrode <NUM>, thus simplifying the preparation process.

In other embodiments, the first electrode <NUM> and the second electrode <NUM> may also adopt a columnar structure or a sponge structure.

It can be understood by those skilled in the art that although the overheat protection device <NUM> shown in <FIG> and <FIG> has a rectangular shape as a whole, this feature does not serve as a limitation of the present disclosure; the overheat protection device <NUM> may have another shape, such as a circular shape and a diamond shape.

An overheat protection device is provided in another embodiment of the present disclosure. <FIG> is a schematic structural view of an overheat protection device according to the embodiment, and <FIG> is a cross-sectional diagram of <FIG> taken along a plane parallel to a Y direction and including an axis of a cylinder. In this embodiment, as shown in <FIG>, an overheat protection device <NUM> includes an insulator. The insulator <NUM> in this embodiment is a hollow tube, of a hollow cylindrical structure. This embodiment is illustrated by taking the hollow cylindrical structure shown in <FIG> as an example.

The overheat protection device <NUM> further includes a first electrode <NUM>, a second electrode <NUM>, and a hot-melt wire <NUM> that are accommodated in the hollow tube. As shown in <FIG>, the first electrode <NUM> and the second electrode <NUM> are respectively disposed in the hollow tube near two ends. The first electrode <NUM> and the second electrode <NUM> are spaced apart by a predetermined distance that is, for example, equal to or greater than <NUM>. Two ends of the hotmelt wire <NUM> are in electrical contact with the first electrode <NUM> and the second electrode <NUM>, respectively. For example, the two ends of the hot-melt wire <NUM> are soldered to the first electrode <NUM> and the second electrode <NUM>, respectively.

The hot-melt wire <NUM> can be made of a conductive material having a lower melting point, such as tin, aluminum-antimony alloy, tin-bismuth alloy, tin-copper alloy, and tin-silver-copper alloy. As a result, when the ambient temperature reaches a predetermined temperature, the hot-melt wire <NUM> is melted and broken, so that the electrical connection between the first electrode <NUM> and the second electrode <NUM> of the overheat protection device <NUM> is broken, and the overheat protection device <NUM> is in an open-circuit state.

The insulator <NUM> of the hollow tubular structure can be made of a material such as ceramic, glass, SiN, and polyimide (PI), so as to ensure that the liquid hot-melt material does not wet the insulator <NUM>. The first electrode <NUM> and the second electrode <NUM> have melting points higher than the melting point of the hot-melt wire <NUM>, and can be made of a material such as Cu, Ag, Au, Ni, and Pd, so as to ensure that the liquid hot-melt material wets the first electrode <NUM> and the second electrode <NUM> of the insulator. As a result, when the hot-melt wire <NUM> is melted when the ambient temperature reaches the predetermined temperature, the liquid hot-melt material flows under the action of surface tension of the liquid hot-melt material, and is collected at the first electrode <NUM> and the second electrode <NUM> that are spaced apart from each other. Substantially, no liquid hot-melt material is present on the inner surface of the insulator <NUM> between the first electrode <NUM> and the second electrode <NUM>. The first electrode <NUM> and the second electrode <NUM> are completely insulated, thereby ensuring that the thermal protection device <NUM> is in a complete open-circuit state.

In this embodiment, the first electrode <NUM> and the second electrode <NUM> may each be a plate-shaped structure, and they enclose a closed space together with the hollow tubular insulator <NUM>.

In some embodiments, the first electrode <NUM> and the second electrode <NUM> may be a sponge electrode which is an electrode block having a porous structure such that the liquid hotmelt material is more easily adsorbed onto the first electrode <NUM> and the second electrode <NUM>. It is thus ensured that the first electrode <NUM> and the second electrode <NUM> are completely insulated and that the thermal protection device <NUM> is in a complete open-circuit state.

A varistor is provided in an embodiment of the present disclosure. The varistor may be an overheat protection varistor, and <FIG> shows a schematic cross-sectional structural view of this type of varistor. As shown in <FIG>, a varistor <NUM> includes a varistor body <NUM> and an overheat protection device disposed on the pressure-sensitive electronic body <NUM>. Various overheat protection devices in the foregoing embodiments may be adopted as the overheat protection device. Here, illustration is made only by taking the overheat protection device <NUM> shown in <FIG> as examples.

As shown in <FIG>, the varistor body <NUM> includes a first electrode layer <NUM>, a varistor chip <NUM>, and a second electrode layer <NUM> disposed sequentially to be stacked. The varistor chip <NUM> may be a metal oxide varistor chip such as a zinc oxide varistor chip. The varistor chip may have various shapes such as a circular shape and a square shape, which is not particularly limited herein. The first electrode layer <NUM> and the second electrode layer <NUM> are respectively disposed on two sides of the varistor chip <NUM>. The first electrode layer <NUM> and the second electrode layer <NUM> can each be made of a metal material, for example, a metal material such as Cu, Ag, and Al, or an alloy thereof. The first electrode layer <NUM> and the second electrode layer <NUM> respectively cover the two sides of the varistor chip <NUM>, and they may have the same shape as the varistor chip <NUM>.

The overheat protection device <NUM> is disposed on one side of the second electrode layer <NUM> away from the first electrode layer <NUM>. The insulator <NUM> of the thermal protection device <NUM> is disposed to face the second electrode layer <NUM>; that is, the first electrode <NUM> and the second electrode <NUM> of the overheat protection device <NUM> are located on one side of the insulator <NUM> away from the second electrode layer <NUM>.

The varistor <NUM> further includes a first lead <NUM> and a second lead <NUM>, wherein the first lead <NUM> is led out by the first electrode layer, the second lead <NUM> is led out by one of the first electrode <NUM> and the second electrode <NUM>, and the second electrode layer <NUM> is electrically connected to the other one of the first electrode <NUM> and the second electrode <NUM>. As shown in <FIG>, in this embodiment, the second lead <NUM> is led out by the second electrode <NUM>, the second electrode layer <NUM> and the first electrode <NUM> are electrically connected by a wire <NUM>, and two ends of the wire <NUM> may be soldered to the second electrode layer <NUM> and the first electrode <NUM>, respectively. The first lead <NUM> and the second lead <NUM> are used to connect the varistor <NUM> to an external circuit.

When a circuit where the varistor <NUM> is located works normally, abnormal overheat does not happen, and the temperature does not reach the fusing condition of the hot-melt wire <NUM> in the varistor <NUM>. In this case, the varistor <NUM> is in a normal working state.

When there is an abnormal voltage in the circuit where the varistor <NUM> is located and the varistor <NUM> has an abnormal overvoltage continuously, or when the temperature of the varistor body <NUM> rises due to another abnormal condition, the varistor body <NUM> conducts heat to the overheat protection device <NUM> located thereon. When the temperature reaches a predetermined temperature, the hot-melt wire <NUM> is melted and broken, such that the electrical connection between the first electrode <NUM> and the second electrode <NUM> of the overheat protection device <NUM> is broken, and the overheat protection device <NUM> is in an open-circuit state. As a result, the circuit where the varistor <NUM> is located is in an open-circuit state, and the varistor body <NUM> is prevented from being continuously overheated and catching on fire.

In this embodiment, as shown in <FIG>, the varistor <NUM> further includes a heat conductive layer <NUM> disposed between the second electrode layer <NUM> and the insulator <NUM> for conducting the heat from the varistor body <NUM> to the overheat protection device <NUM>. The heat conductive layer <NUM> may be a heat conductive adhesive, such that the overheat protection device <NUM> is adhered and fixed to the second electrode layer <NUM> and heat may be conducted. The heat conductive layer <NUM> may also be a solder for soldering and fixing the overheat protection device <NUM> to the second electrode layer <NUM>, and function to conduct heat.

It can be understood by those skilled in the art that the conductive layer <NUM> is optional. In some embodiments, the heat conductive layer <NUM> may be omitted, and the overheat protection device may be directly disposed on the second electrode layer <NUM>.

In some embodiments, the varistor <NUM> may further include an encapsulation layer (not shown in <FIG>) that can integrally clad a combination of the varistor body <NUM> and the overheat protection device <NUM>. The encapsulation layer is for protecting the varistor body <NUM>, the overheat protection device <NUM>, and the like encapsulated therein. The first lead <NUM> and the second lead <NUM> of the varistor <NUM> are led out through the encapsulation layer. The encapsulation layer can be made of an epoxy material.

Claim 1:
An overheat protection device, comprising:
a first electrode (<NUM>) and a second electrode (<NUM>) disposed to be spaced apart;
a hot-melt wire (<NUM>) located between the first electrode and the second electrode, the hot-melt wire being in electrical contact with the first electrode and the second electrode; and
an insulator (<NUM>) supporting the first electrode and the second electrode, wherein
the hot-melt wire is melted into a liquid hot-melt material when the ambient temperature reaches a predetermined temperature, the liquid hot-melt material wets the first electrode and the second electrode, and the liquid hot-melt material does not wet the insulator at least at a portion located between the first electrode and the second electrode;
characterised in that the insulator comprises a cylindrical structure (<NUM>), and the first electrode, the second electrode, and the hot-melt wire are disposed in the cylindrical structure;
and in that at least one of the first electrode and the second electrode is a sponge electrode having a porous structure such that the liquid hotmelt material is more easily adsorbed.