Heat absorbing layer for metal oxide varistor
By using a heat-absorbing layer of a mixture of silica sand, melamine cyanurate, and silicone resin in the TMOV device to absorb heat, the problems of electrical breakdown and overheating in the TMOV device are solved, and more reliable circuit protection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DONGGUAN LITTELFUSE ELECTRONICS CO LTD
- Filing Date
- 2024-12-18
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional thermally protected metal oxide varistors (TMOVs) are prone to electrical breakdown and overheating under high local current, leading to overheating and combustion, and the TCO element may disconnect prematurely.
The heat-absorbing layer is formed from a mixture of silica sand, melamine cyanurate and silicone resin, and is bonded to the second electrode. It is also connected to the TCO element through heat-absorbing paste. The heat-absorbing layer absorbs heat to prevent the TCO element from melting prematurely, and is combined with a dielectric coating to protect the circuit.
The thermal resilience of the TMOV device is enhanced, preventing the TCO element from disconnecting prematurely, effectively blocking current, avoiding continuous arc damage to the circuit, and protecting circuit safety.
Smart Images
Figure CN122245913A_ABST
Abstract
Description
Technical Field
[0001] This disclosure generally relates to the field of circuit protection devices. More particularly, this disclosure relates to thermally protected metal oxide rheostats with enhanced thermal resilience. Background Technology
[0002] A metal oxide varistor (MOV) is a voltage-dependent nonlinear device used in electronic circuits to provide transient voltage suppression. An MOV exhibits high resistance when subjected to low voltages and low resistance when subjected to high voltages. When connected in parallel with protected circuit components, an MOV can clamp the voltage to a safe level in the event of high transient voltages in the circuit. Therefore, the MOV absorbs energy that would otherwise damage the protected components.
[0003] One drawback associated with traditional MOVs is their susceptibility to electrical punch-through when subjected to high local currents, which can lead to overheating and subsequent combustion. For example, in the event of an abnormal overvoltage condition, an MOV may overheat and potentially experience thermal runaway and / or electrical breakdown, whereby the hot gas plume could cause the electrodes on the outer surface of the MOV to rupture. To address this issue, thermally protected MOV (TMOV) devices have been developed. (Reference) Figure 1A and Figure 1B The diagram shows a front perspective view and a rear perspective view of a TMOV device 10 according to the prior art. The TMOV device 10 includes an MOV chip 12 formed of a material having the voltage-dependent nonlinear resistance characteristics described above. The TMOV device 10 also includes a first conductive electrode 14a and a second conductive electrode 14b disposed on opposite sides of the MOV chip 12, and conductive first leads 15 and second leads 16 for facilitating electrical connections within the TMOV device 10 in a circuit. The first lead 15 is directly connected to the first electrode 14a on a first side of the MOV chip 12, and the second lead 16 is connected to a dielectric barrier 17 disposed on a second side of the MOV chip 12. The dielectric barrier 17 prevents direct electrical connection between the second lead 16 and the second electrode 14b. The TMOV device 10 also includes a thermal cutoff (TCO) element 19 having a first end of the second lead 16 electrically connected (e.g., via soldering) to the dielectric barrier 17 and a second end electrically connected to the second electrode 14b. TCO element 19 is formed of a conductive material and is adapted to melt and separate when a predetermined temperature (e.g., 140°C to 240°C) is reached.
[0004] During normal operation, the TMOV device 10 will operate as a conventional MOV device, clamping the voltage to a safe level in the event of a high transient voltage in the connection circuit. However, in the event of an overheating condition in the TMOV device 10, the TCO element 19 will melt and separate, thereby blocking current flow through the TMOV device 10 to prevent thermal runaway and electrical breakdown. The risk of catastrophic failure (e.g., combustion) is thus mitigated.
[0005] In some cases, the TCO element of a TMOV device can disconnect prematurely (i.e., without a real failure condition), such as if the TMOV device is operated for extended periods and / or in a thermal environment. Therefore, it is desirable to provide a TMOV device with enhanced thermal resilience, wherein the TCO element of the TMOV device is less prone to premature disconnection. It is precisely regarding these and other considerations that this improvement can be useful. Summary of the Invention
[0006] This overview is provided to present, in a simplified form, the selection of concepts further described below in the detailed description. This overview is not intended to identify key or substantial features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter.
[0007] A thermally protected metal oxide varistor (TMOV) device according to an embodiment of the present disclosure may include an MOV chip; a first electrode disposed on a first side of the MOV chip; a second electrode disposed on a second side of the MOV chip opposite to the first side; a conductive first lead connected to the first electrode; a heat-absorbing layer bonded to the second electrode by a heat-absorbing paste formed of a mixture of silica sand, melamine cyanurate, and silicone resin, and the heat-absorbing paste being formed of a mixture of melamine cyanurate and silicone resin; a thermal cutoff (TCO) element extending through holes in the heat-absorbing layer and having a first end electrically connected to the second electrode by a certain amount of solder having a melting temperature lower than the melting temperature of the TCO element; and a conductive second lead electrically connected to a second end of the TCO element.
[0008] A thermally protected metal oxide varistor (TMOV) device according to another embodiment of the present disclosure may include: an MOV chip; a conductive first electrode disposed on a first side of the MOV chip; a conductive second electrode disposed on a second side of the MOV chip opposite to the first side; a conductive first lead connected to the first electrode; a heat-absorbing layer bonded to the second electrode by a heat-absorbing paste formed of a mixture of silica sand, melamine cyanurate, and silicone resin, and the heat-absorbing paste being formed of a mixture of melamine cyanurate and silicone resin; a thermal cutoff (TCO) element extending through holes in the heat-absorbing layer and having a first end electrically connected to the second electrode by a certain amount of solder having a melting temperature lower than the melting temperature of the TCO element; and a conductive second lead electrically connected to a second end of the TCO element. Attached Figure Description
[0009] Figure 1A and Figure 1B These are front and rear perspective views showing a thermally protected metal oxide rheostat device according to the prior art;
[0010] Figures 2A to 2C These are front perspective views, rear perspective views, and exploded views of a thermally protected metal oxide rheostat device according to embodiments of the present disclosure; and
[0011] Figures 3A to 3E It shows that Figures 2A to 2C A series of perspective views showing the assembly process of the thermally protected metal oxide rheostat device. Detailed Implementation
[0012] The thermally protected metal oxide varistor (TMOV) device according to this disclosure will now be described more fully with reference to the accompanying drawings. However, TMOV devices can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will convey certain exemplary aspects of the TMOV device to those skilled in the art.
[0013] refer to Figures 2A to 2CThis illustration shows a front view, a rear view, and an exploded view of an exemplary embodiment of a thermally protected metal oxide varistor device 100 (hereinafter referred to as "TMOV device 100") according to the present disclosure. The TMOV device 100 may include an MOV chip 112 having conductive first electrodes 114a and second electrodes 114b disposed on opposite first and second sides thereon. The MOV chip 112 may be formed from any MOV composition known in the art, such as zinc oxide particles embedded in ceramic. The present disclosure is not limited in this respect. The first electrodes 114a and second electrodes 114b of the TMOV device 100 may be formed from metals with good conductivity, including but not limited to aluminum, copper, silver, tin, etc. The present disclosure is not limited in this respect.
[0014] The TMOV device 100 may further include a heat-absorbing layer 113 disposed on a second side of the MOV chip 112, flush with and adjacent to the second electrode 114b. The heat-absorbing layer 113 may be formed from a mixture of silica sand, melamine cyanurate, and silicone resin, which may be cast into a mold, pressed and cured (e.g., hot-pressed at a temperature ranging from room temperature to 170 degrees Celsius) and subsequently stamped or cut into a desired shape (e.g., a disc as shown). In various embodiments, the aforementioned mixture may contain silica sand, melamine cyanurate, and silicone resin in an 8:1:1 ratio. This disclosure is not limited in this respect. The heat-absorbing layer 113 may be attached to the second electrode 114b using a heat-absorbing paste, as further described below.
[0015] The MOV chip 112, the first electrode 114a and the second electrode 114b, and the heat-absorbing layer 113 are depicted as circular in shape, but this is not critical. It is conceivable that one or more of the MOV chip 112, the first electrode 114a and the second electrode 114b, and the heat-absorbing layer 113 may have different shapes, such as rectangular, triangular, irregular shapes, etc., without departing from the scope of this disclosure. The heat-absorbing layer 113 is shown covering the entire second electrode 114b and the entire second side of the MOV chip 112. This disclosure is not limited in this respect. In various non-limiting embodiments, the heat-absorbing layer 113 may cover at least 80% of the second side of the MOV chip.
[0016] The TMOV device 100 may further include a conductive first lead 115 and a second lead 116 for facilitating electrical connections of the TMOV device 100 within a circuit. The first lead 115 may be directly connected to a first electrode 114a on a first side of the MOV chip 112 via soldering, fusion, conductive adhesive, etc. The second lead 116 may be connected to a first end of a thermally cut-off (TCO) element 119, such as with solder 121. The TCO element 119 may extend through an opening 123 formed in the heat-absorbing layer 111 (e.g., via drilling) and may be attached at a second end to a second electrode 114b, such as with solder as further described below. The TCO element 119 may be formed of a conductive material adapted to melt and separate upon reaching a predetermined temperature (e.g., 140°C to 240°C). In various embodiments, the TCO element 119 may be formed of solder having a higher melting temperature than the solder used to connect the TCO element 119 to the second lead 116 and the second electrode 114b.
[0017] refer to Figures 3A to 3E This shows a series of views illustrating the process of assembling the TMOV device 100. Figure 3A In this configuration, the first lead 115 can be electrically connected to the first electrode 114a, and the TCO element 119 can be electrically connected to the second electrode 114b. In various embodiments, the TCO element 119 can be electrically connected to the second electrode 114b using a certain amount of solder 127 having a melting temperature lower than the melting temperature of the solder used to form the TCO element 119 as described above. Therefore, the solder 123 can be heated and reflowed to bond the TCO element 119 to the second electrode 114b without melting it.
[0018] exist Figure 3B In this process, the heat-absorbing paste 130 can be applied to the second electrode 114b and can substantially cover the solder 127 at the junction of the TCO element 119 and the second electrode 114b. The heat-absorbing paste 130 can be formed from a mixture of melamine cyanurate and silicone resin. In various embodiments, the mixture mentioned above can contain melamine cyanurate and silicone resin in a 1:1 ratio. This disclosure is not limited in this respect.
[0019] exist Figure 3C In this configuration, the second lead 116 can be threaded through the opening 123 of the heat-absorbing layer 113, and the heat-absorbing layer 113 can move or slide over the second lead 116 and the TCO element 119, and can be rotated and / or tilted to be flush with the second electrode 114b to cover the second side of the MOV chip 112, as shown below. Figure 3DAs shown. The heat-absorbing paste 130 can then be cured (e.g., at 170 degrees Celsius for 2 to 4 minutes) and the heat-absorbing layer 113 can then be bonded to the second electrode 114b.
[0020] exist Figure 3E In this embodiment, a protective dielectric coating 132 is applied over portions of the MOV chip 112, the first electrode 114a and the second electrode 114b, the heat-absorbing layer 113, the TCO element 119, and the first lead 115 and the second lead 116. In various embodiments, the dielectric coating 132 may be formed of epoxy resin and may be applied via dip coating, spraying, or similar methods. In various embodiments, the dielectric coating 132 may be omitted entirely. This disclosure is not limited in this respect.
[0021] During normal operation of the TMOV device 100, the heat-absorbing layer 113 and the heat-absorbing paste 130 absorb heat to prevent the TCO element 119 from melting / breaking prematurely, which could otherwise occur due to heat buildup in the TMOV device 100 caused by prolonged operation and / or operation in a hot environment. Similarly, the heat-absorbing layer 113 and the heat-absorbing paste 130 can prevent premature melting / breaking of the solder 127 connecting the TCO element 119 to the second electrode and / or the solder 123 connecting the TCO element 119 to the second lead 116.
[0022] In the event of a real fault condition (e.g., an extreme overvoltage condition) in the TMOV device 100, the heat absorption capacity of the heat-absorbing layer 113 and the heat-absorbing paste 130 may be exceeded, and the TCO element 119 may melt, thereby blocking the current flow through the TMOV device 100 and preventing further heating that could ignite the TMOV device 100 and damage surrounding components. When the TCO element 119 disconnects, an electric arc may propagate through the gap left between the separated TCO element 119 and the second electrode 114a. The heat from the arc can burn and decompose the silicone resin in the heat-absorbing layer 113 and / or the heat-absorbing paste 130. As the silicone resin decomposes, melamine cyanurate in the heat-absorbing layer 113 and / or the heat-absorbing paste 130 may be exposed and may also be burned by the heat of the arc. When melamine cyanurate is burned and decomposed, it can undergo an endothermic chemical reaction that absorbs heat. The arc is thus rapidly cooled. Furthermore, some byproducts of the endothermic chemical reaction may be non-conductive gases (e.g., ammonia), which can hinder the arc's ability to persist. Further, other byproducts of the endothermic chemical reaction can produce water, which can further cool the arc. Therefore, the endothermic layer 113 and / or the endothermic paste 130 can absorb heat, release gases detrimental to arc maintenance, and generate water that can further cool the arc in the event of a malfunction in the TMOV device 100, all of which contribute to rapid arc quenching. Components connected to and / or located near the TMOV device 100 are thus protected from damage that would otherwise be possible if the arc were allowed to persist.
[0023] As used herein, elements or operations described in the singular and beginning with the words “a” or “an” should be understood to not exclude elements or operations in the plural form, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” in this disclosure are not intended to exclude the existence of additional embodiments that also incorporate the described features.
[0024] While this disclosure refers to certain embodiments, numerous modifications, alterations, and variations of the described embodiments are possible without departing from the scope and domain of this disclosure, as defined in the appended claims. Therefore, this disclosure is intended to be limited to the described embodiments but has the full scope defined by the following claims and their equivalents.
Claims
1. A thermally protected metal oxide varistor (TMOV) device, the TMOV device comprising: MOV chip; A conductive first electrode is disposed on the first side of the MOV chip. A conductive second electrode is disposed on the second side of the MOV chip opposite to the first side; A conductive first lead is connected to the first electrode; A heat-absorbing layer is disposed on the second electrode; A thermal cutoff (TCO) element, the TCO element extending through the heat-absorbing layer and having a first end electrically connected to the second electrode; as well as A conductive second lead is electrically connected to the second end of the TCO element.
2. The TMOV device according to claim 1, wherein, The TCO element is formed of a conductive material and is adapted to melt and separate upon reaching a predetermined temperature.
3. The TMOV device according to claim 1, wherein, The TCO element is formed from solder.
4. The TMOV device according to claim 1, wherein, The heat-absorbing layer is formed from a mixture including melamine cyanurate.
5. The TMOV device according to claim 4, wherein, The heat-absorbing layer is formed from a mixture comprising silica sand, melamine cyanurate, and silicone resin.
6. The TMOV device according to claim 5, wherein, The heat-absorbing layer is formed from a mixture of silica sand, melamine cyanurate, and silicone resin in a ratio of 8:1:
1.
7. The TMOV device according to claim 1, wherein, The heat-absorbing layer covers at least 80% of the second side of the MOV chip.
8. The TMOV device according to claim 1, wherein, The heat-absorbing layer is bonded to the second electrode using heat-absorbing paste.
9. The TMOV device according to claim 8, wherein, The heat-absorbing paste is formed from a mixture of melamine cyanurate and silicone resin.
10. The TMOV device according to claim 9, wherein, The heat-absorbing paste is formed from a mixture of melamine cyanurate and silicone resin in a 1:1 ratio.
11. The TMOV device according to claim 8, wherein, The heat-absorbing paste covers the junction between the TCO element and the second electrode.
12. The TMOV device according to claim 1, wherein, The TCO element is connected to the second electrode by a certain amount of solder, the solder having a melting temperature lower than that of the TCO element.
13. The TMOV device according to claim 1, wherein, The MOV chip, the first electrode and the second electrode, the heat absorption layer, the TCO element, and portions of the first lead and the second lead are covered by a dielectric coating.
14. The TMOV device according to claim 13, wherein, The dielectric coating is formed of epoxy resin.
15. A thermally protected metal oxide varistor (TMOV) device, the TMOV device comprising: MOV chip; A conductive first electrode is disposed on the first side of the MOV chip. A conductive second electrode is disposed on the second side of the MOV chip opposite to the first side; A conductive first lead is connected to the first electrode; A heat-absorbing layer is bonded to the second electrode by a heat-absorbing paste, the heat-absorbing layer being formed of a mixture of silica sand, melamine cyanurate and silicone resin, and the heat-absorbing paste being formed of a mixture of melamine cyanurate and silicone resin; A thermal cutoff (TCO) element extends through holes in the heat-absorbing layer and has a first end electrically connected to a second electrode by a certain amount of solder having a melting temperature lower than the melting temperature of the TCO element; as well as A conductive second lead is electrically connected to the second end of the TCO element.
16. The TMOV device according to claim 15, wherein, The heat-absorbing layer is formed from a mixture of silica sand, melamine cyanurate, and silicone resin in a ratio of 8:1:
1.
17. The TMOV device according to claim 15, wherein, The heat-absorbing layer covers at least 80% of the second side of the MOV chip.
18. The TMOV device according to claim 15, wherein, The heat-absorbing paste is formed from a mixture of melamine cyanurate and silicone resin in a 1:1 ratio.
19. The TMOV device according to claim 15, wherein, The heat-absorbing paste covers the junction between the TCO element and the second electrode.