WO2020000181A1

WO2020000181A1 - Thermally Protected Metal Oxide Varistor

Info

Publication number: WO2020000181A1
Application number: PCT/CN2018/092866
Authority: WO
Inventors: Dongjian Song; Libing LU
Original assignee: Dongguan Littelfuse Electronics Company Limited
Priority date: 2018-06-26
Filing date: 2018-06-26
Publication date: 2020-01-02
Also published as: CN110859051B; CN110859051A

Abstract

Provided herein is a thermally protected varistor (TPV) device including a varistor body having first and second sides, wherein a thermal electrode is disposed along the second side. A first lead is electrically connected to the first side and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly including a housing and a spring element having a first end disposed within the housing and a second end coupled to a sidewall of the housing. The first end may include a first terminal, and the second end may include a third lead. The terminal assembly may further include an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the spring element.

Description

Thermally Protected Metal Oxide Varistor

Field of the Disclosure

The disclosure relates generally to the protection of electrical and electronic circuits and equipment from power surges and, more particularly, to a thermally-protected varistor having a thermally actuated disconnect.

Background of the Disclosure

Over-voltage protection devices are used to protect electronic circuits and components from damage due to over-voltage fault conditions. These over-voltage protection devices may include metal oxide varistors (MOVs) that are connected between the circuits to be protected, and a ground line. MOVs have a specific current-voltage characteristic that allows them to be used to protect such circuits against catastrophic voltage surges. Typically, these devices utilize spring elements, which can melt during an abnormal condition to form an open circuit. In particular, when a voltage that is larger than the nominal or threshold voltage is applied to the device, current flows through an MOV, which generates heat. This causes the linking element to melt. Once the link melts, an open circuit is created, which prevents the MOV from catching fire.

However, these existing circuit protection devices do not provide an efficient heat transfer from the MOV to the spring element, thereby delaying response times, and subjecting the MOV to periodic transient voltages and overvoltage conditions, which apply further electrical stress. As a result of these stresses MOV′s tend to degrade over time resulting in higher leakage current. At the end of their electrical lives, MOV′s tend to fail catastrophically. End-of-life failures come in various forms. Failure due to fragmentation caused by excessive transient voltage is one type of end-of-life failure. Another failure type is thermal runaway caused by either degradation of the MOV and/or a sustained abnormal overvoltage condition. A thermal disconnect is used to open the device in the event of sustained overvoltage or thermal runaway due in part to the aforementioned electrical stresses noted above. It is desirable to have the thermal disconnect mechanism in very close proximity to the MOV disk so that thermal response time is as fast as possible. Therefore the purpose of a thermal disconnect MOV is to provide for relatively benign failure when subjected to conditions leading to thermal runaway.

Although thermally protected varistors are presently available, the currently available thermal disconnect varistors comprise complicated assemblies and are costly to manufacture. Another drawback of known approaches of thermally protected varistors is that they are one-time use components that must be replaced once the thermal disconnect has been triggered.

Thus, there presently exists a need for an efficiently-constructed varistor for protecting sensitive electrical circuits and equipment from abnormal overvoltage transients that can be easily maintained and serviced. It is with respect to these and other considerations that the present improvements are provided.

Summary of the Disclosure

A TPV device according to one approach may include a varistor body, including a first side, and a thermal electrode disposed along a second side opposite the first side, wherein a first lead is electrically connected to the first side and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly directly coupled to the second side of the varistor body. The terminal assembly may include a housing including a sidewall and a base, and a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing. The first end may include a first terminal, and the second end may include a third lead. The terminal assembly further includes an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element, wherein the first lead, the second lead, and the third lead are each directly physically secured to the housing, and wherein the first lead, the second lead, and the third lead extend along a same plane.

A TPV apparatus according one embodiment of the disclosure may include a varistor body having a first side and a second side opposite the first side, and a thermal electrode disposed along the second side of the varistor body. The TPV apparatus may further include a first lead electrically connected to the first side and a second lead electrically connected to the thermal electrode. The TPV apparatus may further include a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly including a housing including a sidewall and a base, and a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing, the first end including a first terminal, and the second end including a third lead. The TPV apparatus may further include an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element, wherein the first lead, the second lead, and the third lead directly coupled to the housing, and wherein the first lead, the second lead, and the third lead each include adjacent sections extending along a same plane.

A TPV device according to another embodiment of the disclosure may include a varistor body comprising a first side and a second side opposite the first side, and a thermal electrode disposed along the second side of the varistor body. A first lead may be electrically connected to the first side, and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly including a housing having a sidewall and a base, and a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing, the first end including a first terminal, and the second end including a third lead. The terminal assembly may further include an inner electrode disposed within an opening in the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element via a thermal linking material, wherein the housing includes a tab operable to secure the inner electrode to the housing.

Brief Description of the Drawings

The accompanying drawings illustrate exemplary approaches of the disclosed embodiments so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a perspective view of a TPV device according to embodiments of the present disclosure;

FIG. 2 is an exploded view of a terminal assembly of the TPV device of FIG. 1 according to embodiments of the present disclosure;

FIG. 3 is a perspective view of a TPV device according to embodiments of the present disclosure;

FIG. 4 is an exploded view of the TPV device of FIG. 3 according to embodiments of the present disclosure;

FIG. 5 is a perspective view of a TPV device including a housing cover according to embodiment of the present disclosure;

FIG. 6 is a perspective view of a TPV device according to embodiments of the present disclosure;

FIG. 7 is an exploded view of the TPV device of FIG. 6 according to embodiments of the present disclosure;

FIG. 8 is a close-up perspective view of a housing of the TPV device of FIG. 6 according to embodiments of the present disclosure;

FIG. 9 is a perspective view of an inner electrode of the TPV device of FIG. 6 according to embodiments of the present disclosure.

The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the disclosure. The drawings are intended to depict typical embodiments of the disclosure, and therefore should not be considered as limiting in scope. In the drawings, like numbering represents like elements.

Furthermore, certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. Furthermore, for clarity, some reference numbers may be omitted in certain drawings.

Detailed Description

Embodiments in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The system/circuit may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the system and method to those skilled in the art.

For the sake of convenience and clarity, terms such as “top, ” “bottom, ” “upper, ” “lower, ” “vertical, ” “horizontal, ” “lateral, ” and “longitudinal” will be used herein to describe the relative placement and orientation of various components and their constituent parts. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

As used herein, an element or operation recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or operations, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

Furthermore, in the following description and/or claims, the terms “on, ” “overlying, ” “disposed on” and “over” may be used in the following description and claims. “On, ” “overlying, ” “disposed on” and “over” may be used to indicate that two or more elements are in direct physical contact with each other. However, “on, ” , “overlying, ” “disposed on, ” and over, may also mean that two or more elements are not in direct contact with each other. For example, “over” may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and” , it may mean “or” , it may mean “exclusive-or” , it may mean “one” , it may mean “some, but not all” , it may mean “neither” , and/or it may mean “both” , although the scope of claimed subject matter is not limited in this respect.

As will be described herein, provided is a thermally protected varistor (TPV) device including a varistor body having first and second sides, wherein a thermal electrode is disposed along the second side. A first lead is electrically connected to the first side, and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly including a housing and a spring element having a first end disposed within the housing and a second end coupled to a sidewall of the housing. The first end may include a first terminal, and the second end may include a third lead. The terminal assembly may further include an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the spring element. In some embodiments, a thermal linking material connects the spring element and the inner electrode. During an overcurrent condition, the thermal linking material melts and flows when above a melting point, thus creating an insulating gap between the inner electrode and the spring element.

As will be apparent herein, the TPV device of the present disclosure can address the problems of the prior art, namely high cost and low reliability, by forming a highly reliable open circuit using a ceramic fuse coupled with a spring terminal. During an overheating event caused by an abnormal overvoltage condition, the TPV device can protect the circuit from damage.

Tuming now to FIGs. 1-2, TPV assembly/device 10 for use with an electrical circuit according to embodiments of the disclosure will be described. As shown, the TPV device 10 includes a varistor body 12, which in this embodiment has a rectangular or cuboid shape defined generally by an outer perimeter 13. The varistor body 12 includes a first side 16, and a thermal electrode 18 disposed along a second side 20. A first lead 21 is electrically connected to the first side 16, while a second lead 22 is electrically connected to the thermal electrode 18. In some embodiments, the thermal electrode 18 is a metallization layer of ceramic, silver, copper, aluminum, or copper plus aluminum. The first lead 21 and the second lead 22 may be secured to respective first and second sides 16, 20 using a high-temperature solder. Although not shown, the TPV device 10 may be encased/surrounded by a conformal epoxy or other high isolation material.

The TPV device 10 may further include a terminal assembly 24 coupled to the varistor body 12. In some embodiments, the terminal assembly 24 includes a housing 26 having a sidewall 28 and a base 30, wherein the sidewall 28 generally extends around the perimeter of the housing 26. The sidewall 28 and the base 30 define a central cavity 32 containing a spring element 35 therein. The spring element 35 includes a first end 36 disposed within the housing 26 and a second end extending outside of the housing 26. The second end represents a third lead 23. The first end 36 of the spring element 35 is connectable with the thermal electrode 18 via an inner electrode 40 and, optionally, a thermal linking element 42 (e.g., solder) , which couples the spring element 35 to the inner electrode 40 when the thermal linking element 42 is below a melting point. Should the thermal linking element 42 exceed the melting point, for example in the event of an over-voltage condition, the spring element 35 will detach and move away from inner electrode 40 along a direction represented by arrow 43, thus causing the third lead 23 to disconnect from the power supply. The inner electrode 40 may be directly physically and electrically connected to the thermal electrode 18 with a solder (e.g., a high temperature solder) to quickly transfer heat to the thermal linking element 42.

In the non-limiting embodiment shown, the inner electrode 40 is a terminal clip extending through an opening 29 of the sidewall 28 of the housing 26. As best shown in FIG. 2, the terminal clip may include two generally

flat sections

31 and 33, which extend parallel, or substantially parallel, to one another. The

flat sections

31, 33 are connected at a closed end of the terminal clip. The terminal clip may be received by a slot or indentation 48 recessed into the base 30 of the housing 26. Once secured to the housing 26, the terminal clip extends along a front surface 37 and a back surface 39 of the base 30 of the housing 26.

In some embodiments, the first lead 21, the second lead 22, and the third lead 23 are each directly physically secured to the housing 26. For example, the first lead may be press-fitted into a slot 52, the second lead 22 may be press-fitted into a slot 47, and the third lead 23 may be press-fitted into a slot 49. In some embodiments, each of the

slots

52, 47, and 49 includes one or more friction elements or ridges to aid with retention of the leads therein. Furthermore, the housing 26 may include one or more tabs 51 for engaging at least the second lead 22 and the third lead 23.

As shown, each of the first lead 21, the second lead 22, and the third lead 23 include adjacent sections at least partially extending along a same plane (e.g., along the x-y plane) . For example, each of the first lead 21, the second lead 22 and the third lead 23 includes a first end and a second end, wherein each of the second ends extend from the housing 26 of the terminal assembly 24. Each of the second ends extend parallel to one another along the same plane. Providing each of the second ends of the leads in-line along the same plane permits easier placement on a PCB.

In some embodiments, the housing 26 may include a side section 50 extending from the base 30 and from the sidewall 28. As shown, the side section 50 extends perpendicularly, or substantially perpendicularly, from the base 30. The side section 50 may include the slot 52 receiving the first lead 21. The slot 52 may extend from a first side 54 of the housing 26 to a second side 56 of the housing 26. The slot 52 may receive a central section 58 of the first lead 21. The central section 58 and the slot 52 may have a length (e.g., along the z-axis) great enough to accommodate varistor bodies of varying thicknesses, therefore covering all voltage ratings for one disk size platform. In some embodiments, the central section 58 may extend beneath or along the side of the varistor body 12, for example, along the perimeter 13 of the housing 26.

Tuming now to FIGs. 3-4, a thermally-protected varistor (TPV) device 100 for use with an electrical circuit according to embodiments of the disclosure will be described. As shown, the TPV device 100 includes a varistor body 112, which in this embodiment has a rectangular or cuboid shape defined generally by an outer perimeter 113. The varistor body 112 includes a first side 116, and a thermal electrode 118 disposed along a second side 120. A first lead 121 is electrically connected to the first side 116, while a second lead 122 is electrically connected to the thermal electrode 118. In some embodiments, the thermal electrode 118 is a metallization layer of ceramic, silver, copper, aluminum, or copper plus aluminum. The first lead 121 and the second lead 122 may be secured to respective first and

second sides

116, 120 using a high-temperature solder.

The TPV device 100 may further include a terminal assembly 124 coupled to the varistor body 112. In some embodiments, the terminal assembly 124 includes a housing 126 having a sidewall 128 and a base 130, wherein the sidewall 128 generally extends around the perimeter of the housing 126. The sidewall 128 and the base 130 define a central cavity 132 containing a spring element 135 therein. The spring element 135 includes a first end 136 disposed within the housing 126 and a second end extending outside of the housing 126. The second end represents a third lead 123. The first end 136 of the spring element 135 is connectable with the thermal electrode 118 via an inner electrode 140 and, optionally, a thermal linking element (not shown) coupling the spring element 135 to the inner electrode 140 when the thermal linking element is below a melting point. Should the thermal linking element exceed the melting point, for example in the event of an over-voltage condition, the spring element 135 will detach and move away from inner electrode 140, thus causing the third lead 123 to disconnect from the power supply.

In the non-limiting embodiment shown, the inner electrode 140 includes terminal tab 153 extending through an opening 155 (FIG. 4) in the base 130 of the housing 126. The inner electrode 140 may include an electrode section 157 directly physical and electrically coupled to the thermal electrode 118. In some embodiments, the terminal tab 153 may extend perpendicularly, or substantially perpendicularly, from the electrode section 157. Although not shown, the TPV device 100 may further include a conformal epoxy or other high isolation material surrounding the varistor body 112 and the terminal assembly 124.

In some embodiments, the first lead 121, the second lead 122, and the third lead 123 are each directly physically secured to the housing 126. Furthermore, each of the first lead 121, the second lead 122, and the third lead 123 at least partially extend along a same plane. For example, as shown, each of the first lead 121, the second lead 122 and the third lead 123 includes a first end and a second end, wherein each of the second ends extend from the housing 126 of the terminal assembly 124. Each of the second ends extend parallel to one another along the same plane. Providing each of the second ends of the leads in-line along the same plane permits easier placement on a PCB.

In some embodiments, the housing 126 may include a side section 150 extending from the base 130 and from the sidewall 128. As shown, the side section 150 extends perpendicularly, or substantially perpendicularly, from base 130. The side section 150 may include a slot 152 receiving the first lead 121. The slot 152 may extend from a first side 154 of the housing 126 to a second side 156 of the housing 126. The slot 152 may receive a central section 158 of the first lead 121. The central section 158 may have a length (e.g., along the z-axis) selected to accommodate varistor bodies of varying thicknesses. In some embodiments, the central section 158 may extend beneath or along the side of the varistor body 112, for example, along the perimeter 113 of the housing 126.

As shown in FIG. 5, the TPV device 100 (as well as the TPV device 10 of FIGs. 1-2) may further include a cover 160. The cover 160 may be coupled to the housing 126 by a set of pins 162 extending from the base of the housing 126. The cover 160 matingly engages the sidewall 128 of the housing 126 to fully encase the spring element therein. In some non-limiting embodiments, the cover 160 encases only the spring element, while the first lead 121 and the second lead 122 remain uncovered, outside the perimeter 113 of the housing 126. Once the cover 160 is in place, the TPV device 100 may be coated with a conformal epoxy or other high isolation material.

Tuming now to FIGs. 6-7, a TPV device 200 according to embodiments of the present disclosure will be described. The TPV device 200 may include any of the features previously described in relation to the TPV device 10 and TPV device 100 above and, as such, may not be described in full detail for the sake of brevity. As shown, the TPV device 200 may further include a terminal assembly 224 coupled to a varistor body 212 (FIG. 6) . In some embodiments, the terminal assembly 224 includes a housing 226 having a sidewall 228 and a base 230, wherein the sidewall 228 generally extends around the perimeter of the housing 226. The sidewall 228 and the base 230 define a central cavity containing a spring element 235 therein. The spring element 235 includes a first end 236 disposed within the housing 226 and a second end extending outside of the housing 226. The first end 236 of the spring element 235 is connectable with a thermal electrode 218 (FIG. 6) via an inner electrode 240 and, optionally, a thermal linking element 242 (e.g., solder) , which couples the spring element 235 to the inner electrode 240 when the thermal linking element 242 is below a melting point. Should the thermal linking element 242 exceed the melting point, for example in the event of an over-voltage condition, the spring element 235 will detach and move away from inner electrode 240.

Referring now to FIGs. 6-9, the inner electrode 240 will be described in greater detail. In the non-limiting embodiment shown, the inner electrode 240 is a terminal clip extending through an opening 255 of the base 230 of the housing 226. The inner electrode 240 may include a first portion 257 extending through the opening 255 of the housing 226. In exemplary embodiments, the first portion 257 is directly physically and electrically coupled with the thermal electrode 218. The first portion 257 may be connected to the thermal electrode by a solder (e.g., a high-temperature solder) . The inner electrode 240 may further include a second portion 259 extending from the first portion 257. As shown, the second portion 259 may wrap around the sidewall 228 of the housing 226 and make contact with the thermal electrode. The second portion 259 may include a set of

arms

266, 267 separated by a gap 268. In some embodiments, the second portion 259 is secured to the sidewall 228 of the housing by a tab 265 or other fastener. For example, the tab 265 extends through the gap 268, and engages an abutment surface 269 of the second portion 259. As a result, the inner electrode 240 may be snapped into place.

In sum, the TPV device of the present disclosure provides a spring terminal that may quickly disconnect from a ceramic thermal electrode in response to an over-voltage event to provide an open circuit to the power supply. At least the following advantages are offered by embodiments of the present disclosure. Firstly, the TPV device is comparatively simple to assemble and permits automatic production, thus reducing manufacturing costs. Secondly, the TPV device has high reliability under an abnormal overvoltage condition due to the configuration of the spring element. Thirdly, the TPV device provides a quick response to overheating due to the spring element being directly soldered onto the thermal metallization layer of ceramic. Fourthly, the TPV device provides drop-in replacement for existing TMOVs due to the same pin configuration and outline, and due to the use of thermal clips. Fifthly, the TPV device provides a robust disconnection due to the long open circuit distance once the spring element swings open within the housing. Sixthly, one assembly module can cover all voltage ratings of one disk size.

While the present disclosure has been described with reference to certain approaches, numerous modifications, alterations and changes to the described approaches are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claims. Accordingly, it is intended that the present disclosure not be limited to the described approaches, but that it has the full scope defined by the language of the following claims, and equivalents thereof. While the disclosure has been described with reference to certain approaches, numerous modifications, alterations and changes to the described approaches are possible without departing from the spirit and scope of the disclosure, as defined in the appended claims. Accordingly, it is intended that the present disclosure not be limited to the described approaches, but that it has the full scope defined by the language of the following claims, and equivalents thereof.

Claims

A thermally protected varistor (TPV) device, comprising:

a varistor body, comprising:

a first side; and

a thermal electrode disposed along a second side opposite the first side, wherein a first lead is electrically connected to the first side and a second lead is electrically connected to the thermal electrode; and

a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly comprising:

a housing including a sidewall and a base; and

a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing, the first end including a first terminal, and the second end including a third lead; and

an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element,

wherein the first lead, the second lead, and the third lead are each directly physically secured to the housing, and wherein the first lead, the second lead, and the third lead extend along a same plane.
The TPV device of claim 1, wherein each of the first lead, the second lead and the third lead include a first end and a second end, wherein each of the second ends extends from the terminal assembly, and wherein each of the second ends extend parallel to one another along the same plane.
The TPV device of claim 1, wherein the housing further comprises a side section extending from the base, wherein the side section includes a slot receiving the first lead.
The TPV device of claim 3, wherein the slot extends from a first side of the housing to a second side of the housing.
The TPV device of claim 1, the housing further comprising:

a cover; and

a plurality of pins extending from the base, the plurality of pins coupleable with the cover.
The TPV device of claim 1, wherein the inner electrode extends through an opening in the base of the housing.
The TPV device of claim 6, wherein the inner electrode includes one of: a terminal clip engaged with the base of the housing, and a terminal tab extending through the opening of the housing.
The TPV device of claim 7, wherein the terminal clip extends through an opening in the sidewall of the housing, and wherein the terminal clip extends along a front surface and a back surface of the base of the housing.
The TPV device of claim 1, further comprising a thermal linking material in contact with the spring element and the inner electrode, wherein the thermal linking material melts and flows above a melting point to create an insulating gap between the inner electrode and the spring element.
The TPV device of claim 9, wherein the thermal linking material is a low-temperature solder.
A thermally protected varistor (TPV) apparatus, comprising:

a varistor body comprising a first side and a second side opposite the first side; and

a thermal electrode disposed along the second side of the varistor body;

a first lead is electrically connected to the first side and a second lead is electrically connected to the thermal electrode; and

a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly comprising:

a housing including a sidewall and a base; and

a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing, the first end including a first terminal, and the second end including a third lead; and

an inner electrode disposed between the thermal electrode and the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element,

wherein the first lead, the second lead, and the third lead directly coupled to the housing, and wherein the first lead, the second lead, and the third lead each include adjacent sections extending along a same plane.
The TPV apparatus of claim 11, wherein each of the first lead, the second lead and the third lead include a first end and a second end, wherein each of the second ends extends from the terminal assembly, and wherein each of the second ends extend parallel to one another along the same plane.
The TPV apparatus of claim 11, wherein the housing further comprises a side section extending from the base, wherein the side section includes a slot receiving the first lead, and wherein the slot extends from a first side of the housing to a second side of the housing.
The TPV apparatus of claim 11, wherein the inner electrode includes one of: a terminal clip engaged with the base of the housing, and a terminal tab extending through the opening of the housing.
The TPV apparatus of claim 14, further comprising a tab extending from the housing, the tab operable to engage the terminal clip.
The TPV apparatus of claim 15, wherein the terminal clip extends through an opening in the sidewall of the housing, and wherein the terminal clip extends along a front surface and a back surface of the base of the housing.
The TPV apparatus of claim 15, wherein the terminal clip comprises:

a first portion extending through the opening of the housing; and

a second portion extending from the first portion, the second portion secured to the sidewall of the housing by the tab.
The TPV apparatus of claim 11, further comprising a thermal linking material in contact with the spring element and the inner electrode, wherein the thermal linking material melts and flows above a melting point to create an insulating gap between the inner electrode and the spring element.
A thermally protected varistor (TPV) device, comprising:

a varistor body comprising a first side and a second side opposite the first side; and

a thermal electrode disposed along the second side of the varistor body;

a first lead is electrically connected to the first side and a second lead is electrically connected to the thermal electrode; and

a terminal assembly directly coupled to the second side of the varistor body, the terminal assembly comprising:

a housing including a sidewall and a base; and

a spring element having a first end disposed within the housing and a second end coupled to the sidewall of the housing, the first end including a first terminal, and the second end including a third lead; and

an inner electrode disposed within an opening in the base of the housing, the inner electrode operable to maintain direct physical contact with the first end of the spring element via a thermal linking material,

wherein the housing includes a tab operable to secure the inner electrode to the housing.
The TPV device of claim 19, wherein the wherein the inner electrode comprises:

a first portion extending through the opening of the housing; and

a second portion extending from the first portion, the second portion secured to the sidewall of the housing by the tab.