WO2019071588A1

WO2019071588A1 - Thermally protected metal oxide varistor

Info

Publication number: WO2019071588A1
Application number: PCT/CN2017/106133
Authority: WO
Inventors: Dongjian Song; Libing LU
Original assignee: Dongguan Littelfuse Electronics Co., Ltd
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2019-04-18
Also published as: CN110024054B; CN109923625B; WO2019071841A1; CN110024054A; CN109923625A

Abstract

Provided herein are thermally protected varistor (TPV) devices. The TPV device further includes a terminal assembly coupled to the varistor body, the terminal assembly including a housing having a sidewall and a base, the base including an opening formed therethrough. A spring element (e.g., a spring element) of the terminal assembly includes a first end disposed within the housing and a second end extending outside of the housing. A first terminal of the spring element engages a thermal electrode of the varistor body through the opening of the base, and either maintains or breaks contact depending on whether a thermal linking material (e.g., solder) coupling the thermal electrode to the spring element is below or above a melting point (e.g., during an over-voltage fault condition). The TPV device may further include an inner electrode extending through the opening in the base of the housing for engagement 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. As the thermal disconnect is typically enclosed in a casing, an individual maintaining the equipment may be unable to easily determine when the thermal disconnect has been triggered and needs to be replaced.

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

In one approach according to the present disclosure, a thermally protected varistor (TPV) device may include a varistor body having an electrode disposed along 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 electrode and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly coupled to the varistor body, the terminal assembly including a housing including a sidewall and a base, wherein an opening is provided in the base, and a spring element having a first end disposed within the housing and a second end extending outside of the housing. A first terminal at the first end of the spring element is connectable with the thermal electrode through the opening of the base to maintain the spring element in physical contact with the thermal electrode when a thermal linking material coupling the spring element and the thermal electrode is below a melting point. Furthermore, a second terminal at the second end of the spring element may be connected to a third lead.

In another approach according to the present disclosure, a thermally protected varistor (TPV) device includes a varistor body having an electrode disposed along 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 electrode and a second lead is electrically connected to the thermal electrode. The TPV device may further include a terminal assembly coupled to the varistor body, the terminal assembly including a housing including a sidewall and a base, wherein an opening is provided in the base for electrical connection with the thermal electrode, and a spring element having a first end disposed within the housing and a second end extending outside of the housing through a slot in the sidewall. The first end may be connectable with the thermal electrode through the opening of the base to maintain the spring element in physical contact with the thermal electrode via a thermal linking material when the thermal linking material is below a thermal threshold. Furthermore, a second terminal at the second end may be connected to a third lead.

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 depicts a circuit diagram including a TPV device according to embodiments of the present disclosure；

FIGs. 2-5 depict a TPV device according to embodiment of the present disclosure；

FIGs. 6-9 depict a terminal assembly of the TPV device of FIGs. 2-5 according to embodiments of the present disclosure；

FIG. 10 depicts a spring element of the TPV device of FIGs. 2-5 according to embodiments of the present disclosure；

FIG. 11 depicts a TPV device according to embodiment of the present disclosure；

FIG. 12 depicts a terminal assembly of the TPV device of FIG. 11 according to exemplary embodiments of the present disclosure；

FIGs. 13-15 depict a TPV device according to embodiments of the present disclosure；

FIGs. 16-17 depict a terminal assembly of the TPV device of FIGs. 13-15 according to embodiments of the present disclosure；

FIG. 18 depicts a spring element of the TPV device of FIGs. 13-15 according to embodiments of the present disclosure；

FIGs. 19-21 depict a TPV device according to embodiments of the present disclosure； and

FIG. 22 depicts a spring element of the TPV device of FIGs. 19-21 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 electrodes connected to multiple leads. The TPV device further includes a terminal assembly coupled to the varistor body, the terminal assembly including a housing having a sidewall and a base, the base including an opening formed therethrough for connection between a thermal electrode of the varistor body and a terminal. A spring element (e.g., a metal contact/terminal exhibiting spring characteristics) of the terminal assembly includes a first end disposed within the housing and a second end extending outside of the housing. The terminal of the spring element engages the thermal electrode of the varistor body, and either maintains or breaks contact depending on whether a thermal linking material (e.g., solder) coupling the thermal electrode to the spring element is below or above a thermal threshold, such as a melting point during an over-voltage fault condition. The TPV device may further include an inner electrode extending through the opening in the base of the housing for engagement with 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.

Turning now to FIG. 1, a thermally-protected varistor (TPV) device 10 for use with an electrical circuit 2 according to embodiments of the disclosure will be described. The simplified electrical circuit 2 generally comprises the TPV device 10, a power source 3, and protected electrical circuit or equipment 4. As will be understood by those skilled in the art, during normal operation, the TPV device 10, which may be positioned in parallel between a first terminal of the power source 3 and the protected electrical circuit 4, is in a closed, or conducting, position, and the protected electrical circuit 4 is powered by the power source 3. As will be described below, in an overvoltage situation, the TPV device 10 opens (as depicted) . The electrical circuit 2 described herein is not intended to be limiting, but merely provides an illustrative example of a general electrical circuit for context.

Turning now to FIGs. 2-4, the TPV device 10 according to embodiments of the disclosure will be described in greater detail. As shown, the TPV device 10 includes a varistor body 12, which in this embodiment has a circular or disk shape defined generally by an outer perimeter 13. The varistor body 12 includes a first electrode 14 disposed along 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 electrode 14, 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 TPV device 10 may further include a terminal assembly 24 (FIG. 4) 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 37 extending outside of the housing 26. The second end 37 is connected to a third lead 23. As will be described in greater detail below, a first terminal at the first end 36 is connectable with the thermal electrode 18 through an opening of the base 30 to maintain the spring element 35 in physical/electrical contact with the thermal electrode 18 when a thermal linking element (e.g., solder) coupling the spring element 35 to the thermal electrode 18 is below a melting point. Should the thermal linking element exceed the melting point, for example in the event of an over-current condition, the spring element 35 will detach and move away from the thermal electrode 18 exposed through the opening 44, thus causing the third lead 23 to disconnect from the power supply.

The TPV device 10 further includes a housing cover 39 coupled to the housing 26 and/or the varistor body 12. In some embodiments, the housing cover 39 may generally follow the shape of the housing 26. As shown, the housing cover 39 may take on a mushroom shape defined by a head 40, a neck 41, and a pair of cutouts 42. As best shown in FIG. 2, the pair of cutouts 42 provide an area for the second lead 22 to access/contact the thermal electrode 18. In some embodiments, the housing cover 39 may include an opening or slot 43 through the neck 41 from which the second end 37 of the spring element 35 may protrude. Although not shown, the TPV device 10 may further include a conformal epoxy or other high isolation material surrounding the varistor body 12, the terminal assembly 24, and the housing cover 39.

Turning now to FIGs. 5-9, the terminal assembly 24 of the TPV device 10 according to embodiments of the disclosure will be described in greater detail. As shown, the terminal assembly 24 includes the spring element 35 secured to the thermal electrode 18 via an opening 44 formed through the base 30 of housing 26. More specifically, a first terminal 45 at the first end 36 of the spring element 35 may be connected to the thermal electrode 18 using a thermal linking material 48, such as a low-temperature solder. The first terminal 45 may include one or more protrusions 50 extending therefrom, so as to allow for areas of accumulation of the thermal linking material 48 between the first end 36 of the spring element 35 and the thermal electrode 18. In some embodiments, the thermal linking material 48 is primarily disposed along the exposed surface of the thermal electrode 18. In other embodiments, the thermal linking material 48 is primarily disposed along the first end 36 of the spring element 35.

When the thermal linking material 48 is below a melting point, physical/electrical contact between the first terminal 45 and the thermal electrode 18 is maintained, causing the first terminal 45 to be positioned over the opening 44. However, when the thermal electrode 18 heats up and the melting point of the thermal linking material 48 is exceeded, the thermal linking material 48 melts and starts to flow, thus creating an insulating gap between the thermal electrode 18 and first terminal 45 of the spring element 35. During an over-current event, the first end 36 of the spring element 35 is configured to move, due to the biasing spring force of the spring element 35, from the position shown in FIGs. 5-6, to the position shown in FIGs. 7-8. In some embodiments, the first end 36 of the spring element 35 is received within a guide area 49, which is recessed into the base 30 of the housing 26, when the spring element 35 disconnects from the thermal electrode 18. The guide area 49 may provide clearance for the protrusion 50 as the spring element 35 swings within the cavity 32 of the housing 26.

As further shown, the terminal assembly 24 may include one or more terminal clips 51 secured to the housing 26 and the varistor body 12. In some embodiments, the terminal clips 51 are each substantially U-shaped fasteners secured about an attachment member 52 extending from the sidewall 28 of the housing 26. One leg of the terminal clip 51 may extend substantially parallel to a bottom surface 53 of the base 30 of the housing 26, for example, as best shown in FIG. 6. The other leg may include a ridge or lip 55, which is a mechanical piece designed to mate or engage with a corresponding surface feature (e.g., an indentation) of the attachment member 52 to secure the terminal clip 51 in place. An outer surface 54 of each terminal clip 51 may be secured (e.g., by high temperature solder) to the varistor body 12, e.g., directly to the thermal electrode 18. During assembly, the terminal clips 51 may be secured to the varistor body 12 first, such that the housing 26 may then be snapped into place during assembly. However, it will be appreciated that the above attachment configuration is non-limiting, as other arrangements for releasably securing the housing 26 to the varistor body 12 are possible within the scope of the present disclosure. Furthermore, the terminal clips 51 are not limited to any particular material, but may include pre-tinned SUS or pre-tinned steel in exemplary embodiments.

The housing 26 of the terminal assembly 24 further includes a first support wall 57 and a second support wall 58 defining a channel 59 for receiving and securing the spring element 35 therein. The channel 59 defines an opening or slot 60 extending through the sidewall 28 to permit the second end 37 of the spring element 35 to extend outside of the housing 26 for connection with the third lead 23. The housing 26 further includes a support post 62 adjacent to and extending from the first support wall 57. As shown, the spring element 35 bends at least partially around the support post 62 to provide tension to the spring element 35. In some embodiments, the housing 26 may be a high temperature plastic or resin, such as polyphenylene sulfide (PPS) , liquid crystal polymer (LCP) , or the like.

As best shown in FIG. 9, the spring element 35 includes a central section 65 extending between the first end 36 and the second end 37, wherein the central section 65 may include one or more bending features to mitigate stress concentration due to fatigue and the temperature fluctuations over time. For example, the central section 65 may include a first bend 66 proximate the first end 36, and a second bend 67 between the first bend 66 and the second end 37. The second bend 67 is located proximate a corner joint 68, which has a first section 69 configured to extend through the channel 59 of the housing 26, and a second section 70 configured to extend through the slot 60. As further shown, the first terminal 45 may extend perpendicular from the central section 65 to enable contact with thermal electrode 18. Although not limited to any particular material, the spring element 35 may be beryllium copper, tin bronze, or other flexible metallic material.

In some embodiments, the corner joint 68 has a first height dimension H1 that is larger/longer than a second height dimension H2 of the adjacent central section 65 and the first end 36. The height differential between H1 and H2 is designed to allow the spring element 35 to swing freely with minimal friction from the base 30 of the housing 26 during an over-current event. As further shown, the second end 37 of the spring element 35 further includes a second terminal 74 for electrically/physically coupling the spring element 35 with the third lead 23. In some embodiments, the second terminal 74 may include

sidewalls

80, 81 defining a channel 73 for receiving the third lead 23 therein. The second terminal 74 extends perpendicularly from the second section 70 of the corner joint 68, towards a center line L-L of the housing 26. In some embodiments, the second terminal 74 may extend beyond the outer perimeter 13 of the varistor body 12. For example, in the case that the varistor body 12 is based on an 18mm (diameter) ceramic "13" , the second terminal 74 may extend beyond the perimeter 13. However, it will be appreciated that the second terminal 74 may not protrude so far in other embodiments, for example, in which a 20mm ceramic "13" is being used.

Turning now to FIG. 10, another embodiment of the first end 36 of the spring element 35 will be described in greater detail. As shown, the first end 36 may include a set of

protrusions

75, 76 extending outwardly from the first terminal 45. In this embodiment, the

protrusions

75, 76 extend perpendicular, or substantially perpendicular, from a surface 77 of the first terminal 45. During connection of the spring element 35 to the thermal electrode, the thermal linking material 48, such as a low-temperature solder, may be provided between the

protrusions

75, 76. Without the

protrusions

75 and 76, the thermal linking material 48 is susceptible to being squeezed away from the first end 36 when the spring element 35 is brought into contact with the thermal electrode 18. More specifically, the

protrusions

75, 76 keep a specific gap between the terminal 45 and the thermal electrode 18, and making sure enough of the thermal linking material 48 is present to provide suitable soldering strength at the intersection therebetween.

Turning now to FIGs. 11-12, another TPV device 110 according to embodiments of the present disclosure will be described in greater detail. As shown, the TPV device 110 includes many the features previously described in relation to the TPV device 10 of FIGs. 1-10 and, as such, will not be described in full detail for the sake of brevity. In this embodiment, the TPV device 110 includes a varistor body 112, which takes on a square or cuboid shape defined by a perimeter 113. The varistor body 112 includes a first electrode (not shown) disposed along 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 electrode, 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 TPV device 110 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 137 extending outside of the housing 126, wherein the second end 137 is connected to a third lead 123.

As shown, a first terminal 145 at the first end 136 of the spring element 135 is connectable with the thermal electrode 118 through an opening 144 of the base 130 to maintain the spring element 135 in physical/electrical contact with the thermal electrode 118 when a thermal linking element (e.g., solder) coupling the spring element 135 to the thermal electrode 118 is below a melting point. Should the thermal linking element exceed the melting point, for example during an over-current event, the spring element 135 will detach and move away (as shown) from the exposed portion of the thermal electrode 118, thus causing the third lead 123 to disconnect from the power supply. Although not shown, the TPV device 110 may further includes a housing cover coupled to the housing 126 and/or the varistor body 112.

As further shown, the second end 137 of the spring element 135 further includes a second terminal 174 for electrically/physically coupling the spring element 135 with the third lead 123. In some embodiments, the second terminal 174 may include sidewalls 180, 181 defining a channel 173 for receiving an end of the third lead 123 therein. The second terminal 174 may extend perpendicularly from a second section 170 of a corner joint 168 of the spring element 135, away from a center line L-L of the housing 126. In some embodiments, the second terminal 174 is separated from the thermal electrode 118 by a gap, which may be filled with epoxy coating material or other isolation materials to provide enough di-electric strength between the second terminal 174 and the thermal electrode 118.

The terminal assembly 124 may include one or more terminal clips 151 secured to the housing 126 and the varistor body 112. In some embodiments, the terminal clip (s) 151 is a substantially U-shaped fastener secured to the housing 126. In the embodiment shown in FIG. 12, the terminal clip 151 may extend entirely across the housing 126, wrapping around the sidewall 128. In some embodiments, the terminal clip 151 may be provided within a recess 182 formed in a bottom surface 153 of the base 130 of the housing 126, An outer surface 154 of the terminal clip 151 may be secured (e.g., by high temperature solder) to the varistor body 112. In some embodiments, the terminal clip 151 is directly attached to the thermal electrode 118. During assembly, the terminal clip 151 may be secured to the varistor body 112 first, such that the housing 126 may then be snapped into place. In some embodiments, the terminal clip 151 may include pre-tinned SUS or pre-tinned steel.

Turning now to FIGs. 13-15, a TPV device 210 according to embodiments of the present disclosure will be described in greater detail. As shown, the TPV device 210 includes a varistor body 212, which in this embodiment has a circular or disk shape defined by an outer perimeter 213. The varistor body 212 includes a first electrode (not shown) disposed along a first side 216, and a thermal electrode 218 disposed along a second side 220. A first lead 221 is electrically connected to the first electrode, while a second lead 222 is electrically connected to the thermal electrode 218. In some embodiments, the thermal electrode 218 is a metallization layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 210 may further include a terminal assembly 224 coupled to the varistor body 212. In some embodiments, the terminal assembly 224 includes a housing 226 having a sidewall 28 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 232 containing a spring element 235 therein. The spring element 235 includes a first end 236 disposed within the housing 226 and a second end 237 extending outside of the housing 226, wherein the second end 237 is connected to a third lead 223. As will be described in greater detail below, a first terminal at the first end 236 is connectable with the thermal electrode 218 through an opening of the base 230 to couple the spring element 235 to the thermal electrode 218 when a thermal linking element (e.g., solder) coupling the spring element 235 to the thermal electrode 218 is below a melting point. Should the thermal linking element exceed the melting point, for example in the event of an over-current condition, the spring element 235 will release and begin to move, thus causing the third lead 223 to disconnect from the power supply.

The TPV device 210 further includes a housing cover 239 coupled to the housing 226 and/or the varistor body 212. In some embodiments, the housing cover 239 may generally follow the shape of the housing 226. For example, the housing cover 239 may take on a generally circular shape with a flat side 279 extending parallel or substantially parallel to the second lead 222. The flat side 279 may provide an area for the second lead 222 to access/contact the thermal electrode 218. As best shown in FIG. 14, the housing cover 239 may include an opening or slot 243 through a sidewall 241 from which the second end 237 of the spring element 235 may protrude. Although not shown, the housing cover 239 and the housing 226 may be covered by a conformal epoxy or other high isolation material.

Turning now to FIGs. 15-17, the terminal assembly 224 of the TPV device 210 according to embodiments of the disclosure will be described in greater detail. As shown, the terminal assembly 224 may include an inner electrode 283 disposed between the thermal electrode 218 and the housing 226. That is, the inner electrode 283 may include an outer surface 284 of a main body 289 that is planar, or substantially planar, with a bottom surface 253 of the base 230 of the housing 226. The main body 289 may be directly coupled to the thermal electrode 218, for example, using a high-temperature solder. In some embodiments, the housing 226 may include a recessed area 286 sized to accept the inner electrode 283 therein.

As shown, the inner electrode 283 may include a front tab 295, a third terminal 285, and a terminal tab 287, wherein the third terminal 285 and the terminal tab 287 extend perpendicular, or substantially perpendicular, from the main body 289. The third terminal 285 is configured to extend through the opening 244 provided through the base 230 of the housing 226. During use, the spring element 235 may be secured to the third terminal 285 of the inner electrode 283, for example using a thermal linking material (not shown) , such as a low-temperature solder. When the thermal linking material is below a melting point, physical/electrical contact between the third terminal 285 and the spring element 235 is maintained. However, when the third terminal 285 heats up and the melting point of the thermal linking material is exceeded, the thermal linking material melts and starts to flow, thus creating an insulating gap between the third terminal 285 and the spring element 235. That is, during an over-current event, the first end 236 of the spring element 235 begins to move, due to the biasing spring force of the spring element 235, away from the third terminal 285.

The housing 226 of the terminal assembly 224 may include a first support wall 257 and a second support wall 258 defining a channel 259 for receiving and securing the spring element 235 therein. The channel 259 extends to an opening or slot 260 provided through the sidewall 228 to permit the second end 237 of the spring element 235 to extend outside of the housing 226 for connection with the third lead 223. The housing 226 further includes a support post 262 adjacent to and extending from the first support wall 257. As shown, the spring element 235 bends at least partially around the support post 262 to provide tension to the first end 236 of the spring element 235. In some embodiments, the housing 226 may be a high temperature plastic or resin, such as polyphenylene sulfide (PPS) , liquid crystal polymer (LCP) , or the like.

As further shown, the housing 226 may include a buttress 290 extending from an inner surface 291 of the base 230. The buttress 290 may connect to the sidewall 228, and includes three (3) sides partially surrounding the opening 244 and the third terminal 285. The buttress 290 serves as a physical support or barrier for the third terminal 285, while still allowing access to the third terminal 285 by the spring element 235.

To accommodate the terminal tab 287, the housing 226 may further include a capping wall 292 extending from the inner surface 291 of the base 230. Once the inner electrode 283 is coupled to the housing 226, the terminal tab 287 extends into an internal slot (not shown) . The terminal tab 287 may be provided for structural symmetry with the third terminal 285 and to provide additional support to the inner electrode 283 once coupled to the housing 226. As shown, for securely attaching the inner electrode 283 to the housing 226, each of the third terminal 285 and the terminal tab 287 may include fasteners, clasps, or surface features 294 extending outwardly for engagement with corresponding fastening features (not shown) within the buttress 290 and the capping wall 292, respectively. Furthermore, in some embodiments, the front tab 295 of the inner electrode 283 may extend into an alignment indentation 296 formed in the main body 289 of the housing 226.

Turning now to FIG. 18, the spring element 235 according to embodiments of the present disclosure will be described in greater detail. As shown, the spring element 235 may be a flat spring terminal including a central section 265 extending between the first end 236 and the second end 237. The central section 265 may include one or more bends or curves provided to mitigate stress concentration stemming from fatigue and temperature fluctuations. For example, the central section 265 may include a first bend 266 proximate the first end 236, and a second bend 267 provided between the first bend 266 and the second end 237, wherein the second bend 267 may include a spring slot 297 to promote bending and reduce stress at that point along the spring element 235. The second bend 267 may be located proximate a corner joint 268, which has a first section 269 configured to extend through the channel 259 of the housing 226, and a second section 270 configured to extend through the slot 260. As further shown, the protrusion 250 may extend perpendicularly away from the first end 236 to enable contact with the third terminal 285. Although not shown, the first end 236 and the protrusion 250 may include a covering of thermally linking solder material.

In some embodiments, the corner joint 268 has a first height dimension H1 that is larger/longer than a second height dimension H2 of the adjacent central section 265 and the first end 236. The height differential between H1 and H2 is designed to allow the spring element 235 to swing freely with minimal friction between the central section 265 and the base 230 of the housing 226 during an over-current event.

As further shown, the second end 237 of the spring element 235 may include a second terminal 274 for electrically/physically coupling the spring element 235 with the third lead (not shown) . In some embodiments, the second terminal 274 may include

sidewalls

280, 281 defining a channel 273 for receiving the third lead therein. The second terminal 274 generally extends perpendicularly from the second section 270 of the corner joint 268, for example, towards a center line of the housing 226. In some embodiments, the second terminal 274 may extend beyond the outer perimeter 213 of the varistor body 212, for example, as shown in FIG. 15.

Turning now to FIGs. 19-21, another TPV device 310 according to embodiments of the present disclosure will be described in greater detail. As shown, the TPV device 310 includes a varistor body 312, which in this embodiment has a square or cuboid shape defined by an outer perimeter 313. The varistor body 312 includes a first electrode (not shown) disposed along a first side 316, and a thermal electrode 318 disposed along a second side 320. A first lead 321 is electrically connected to the first electrode, while a second lead 322 is electrically connected to the thermal electrode 318. In some embodiments, the thermal electrode 318 is a metallization layer of ceramic, silver, copper, aluminum, or copper plus aluminum.

The TPV device 310 may further include a terminal assembly 324 coupled to the varistor body 312. In some embodiments, the terminal assembly 324 includes a housing 326 having a sidewall 328 and a base 330, wherein the sidewall 328 generally extends around the perimeter of the housing 326. The sidewall 328 and the base 330 define a central cavity 332 containing a spring element 335 therein.

As shown, the terminal assembly 324 may include an inner electrode 383 disposed between the thermal electrode 318 and the housing 326. That is, the inner electrode 383 may include an outer surface of a main body 389 that is coupled to the thermal electrode 318 and extends planar, or substantially planar, along a bottom surface of the base 330 of the housing 326. The inner electrode 383 may include a front tab 395, and a third terminal 385 and a terminal tab 387 extending perpendicular, or substantially perpendicular, from the main body 389. In some embodiments, the housing 326 may include a recessed area in the base 330 sized to accept the inner electrode 383 therein.

The TPV device 310 further includes a housing cover 339 coupled to the housing 326 and/or the varistor body 312. As shown, the sidewall 328 of the housing 326 may engage the housing cover 339 using a set of fasteners 398. In some embodiments, the set of fasteners 398 include one or more tabs or protrusions that snap-fit into a corresponding openings. The housing cover 339 may further include one or more relief slots 399 to provide flexibility to the housing cover 339 as the housing cover 339 is attached to the housing 326.

As shown, the housing cover 339 may generally follow the shape of the housing 326, although embodiments herein are not limited to any particular shape. For example, the housing cover 339 may take on a generally square or rectangular shape. As best shown in FIG. 19, the housing cover 339 may include one or more flat sides 379 extending parallel or substantially parallel with an end portion of the second lead 322. The flat side 379 may provide an area for the second lead 322 to access/contact the thermal electrode 318. The housing cover 339 may include an opening or slot 343 through the flat side 379 from which the spring element 335 may protrude. Although not shown, the housing cover 339 and the housing 326 may be covered by a conformal epoxy or other high isolation material.

Turning now to FIG. 21, the terminal assembly 324 of the TPV device 310 according to embodiments of the disclosure will be described in greater detail. The spring element 335 includes a first end 336 disposed within the housing 326 and a second end 337 extending outside of the housing 326, wherein the second end 337 is connected to a third lead 323 (FIGs. 19-20) . As shown, the third terminal 385 may extend through the opening 344 provided through the base 330 of the housing 326. The spring element 335 is configured to be secured to the third terminal 385 of the inner electrode 383, for example, using a thermal linking material (not shown) , such as a low-temperature solder. When the thermal linking material is below a melting point, physical/electrical contact between the third terminal 385 and the spring element 335 is maintained. However, when the third terminal 385 heats up and the melting point of the thermal linking material is exceeded, the thermal linking material melts and starts to flow, thus creating an insulating gap between the third terminal 385 and the spring element 335. That is, during an over-current event, the first end 336 of the spring element 335 begins to move, due to the biasing spring force of the spring element 335, away from the third terminal 385.

The housing 326 of the terminal assembly 324 may include a first support wall 357 and a second support wall 358 defining a channel 359 for receiving and securing the spring element 335 within the housing 326. The channel 359 extends to an opening or slot 360 provided through the sidewall 328 to permit the second end 337 of the spring element 335 to extend outside of the housing 326 for connection with the third lead 323. The housing 326 further includes a support post 362 adjacent to and extending from the first support wall 357. As shown, the spring element 335 bends at least partially around the support post 362 to provide tension to the first end 336 of the spring element 335.

As further shown, the housing 326 may include a buttress 390 extending from an inner surface 391 of the base 330. The buttress 390 may connect to the sidewall 328, and includes three (3) sides partially surrounding the opening 344 and the third terminal 385. The buttress 390 serves as a physical support or barrier for the third terminal 385, while still allowing access to the third terminal 385 by the first end 336 of the spring element 335.

To accommodate the terminal tab 387, the housing 326 may further include a capping wall 392 extending from the inner surface 391 of the base 230. Once the inner electrode 383 is coupled to the housing 326, the terminal tab 387 extends into an internal slot (not shown) of the capping wall 392. In this embodiment, the terminal tab 387 is provided for structural symmetry with the third terminal 385 and to provide additional support to the inner electrode 383 once coupled to the housing 326. For securely attaching the inner electrode to the housing 326, each of the third terminal 385 and the terminal tab 387 may include fasteners, clasps, or surface features (not shown) extending outwardly for engagement with corresponding fastening features within the buttress 390 and the capping wall 392, respectively. Furthermore, in some embodiments, the front tab 395 of the inner electrode 383 may extend into an alignment indentation 396 formed in the main body 389 of the housing 326.

Turning now to FIG. 22, the spring element 335 according to embodiments of the present disclosure will be described in greater detail. As shown, the spring element 335 may be a flat spring terminal including a central section 365 extending between the first end 336 and the second end 337. The central section 365 may include one or more bends or curves provided to mitigate stress concentration stemming from fatigue and temperature fluctuations. For example, the central section 365 may include a first bend 366 proximate the first end 336, and a second bend 367 provided between the first bend 366 and the second end 337, wherein the second bend 367 may include a spring slot 397 to promote bending and reduce stress at that point along the spring element 335. The second bend 367 may be located proximate a channel section 368, which is generally straight, and which is configured to extend through the channel 359 of the housing 326. The channel section 368 may include a side tab 369 configured to engage a sidewall slot 361 (FIG. 21) for securing the spring element 335 within the housing 326. As shown, the side tab 369 may extend perpendicularly, or substantially perpendicularly, from the channel section 368. As further shown, the first end 336 may include the protrusion 350 extending away from the spring element 335 to enable contact with the third terminal 385. Although not shown, the first end 336 and the protrusion 350 may include a covering or layer of solder material.

In some embodiments, the channel section 368 has a first height dimension H1 that is larger/longer than a second height dimension H2 of the adjacent central section 365 and of the first end 336. The height differential between H1 and H2 is designed to allow the spring element 335 to swing freely with minimal friction between the central section 365 and the base 330 of the housing 326 during an over-current event.

As further shown, the second end 337 of the spring element 335 may include a second terminal 374 for electrically/physically coupling the spring element 335 with the third lead (not shown) . In some embodiments, the second terminal 374 may include

sidewalls

380 and 381 defining a channel 373 for receiving the third lead therein. The second terminal 374 generally extends parallel from the channel section 368. In some embodiments, the second terminal 374 is supported above or away from the thermal electrode 318. For example, the second terminal 374 may be separated from the thermal electrode 318 by a gap, which may be filled with epoxy coating material or other isolation materials to provide enough di-electric strength between the second terminal 374 and the thermal electrode 318.

In sum, the TPV device of the present disclosure provides a flat spring terminal that may quickly disconnect from a ceramic thermal electrode in response to an over-current 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:

an electrode disposed along 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 electrode and a second lead is electrically connected to the thermal electrode； and

a terminal assembly coupled to the varistor body, the terminal assembly comprising:

a housing including a sidewall and a base, wherein an opening is provided in the base； and

a spring element having a first end disposed within the housing and a second end extending outside of the housing, wherein a first terminal at the first end is connectable with the thermal electrode through the opening of the base to maintain the spring element in physical contact with the thermal electrode when a thermal linking material coupling the spring element and the thermal electrode is below a melting point, and

wherein a second terminal at the second end is connected to a third lead.
The TPV device of claim 1, the terminal assembly further comprising a housing cover coupled to the housing.
The TPV device of claim 1, wherein the thermal linking material melts and flows above the melting point to create an insulating gap between the thermal electrode and the first terminal of the spring element.
The TPV device of claim 1, the housing of the terminal assembly further comprising:

a set of support walls defining a channel receiving the spring element；

a slot extending through the sidewall, the slot receiving the spring element from the channel； and

a support post adjacent the set of support walls, wherein the spring element bends at least partially around the support post.
The TPV device of claim 1, wherein the thermal linking material is a low-temperature solder.
The TPV device of claim 1, the terminal assembly further comprising a terminal clip coupling the varistor body with the housing.
The TPV device of claim 2, wherein the housing cover includes at least one flat side extending substantially parallel to the second lead.
The TPV device of claim 1, the terminal assembly further comprising an inner electrode disposed between the thermal electrode and the housing, the inner electrode comprising:

a main body extending along the base of the housing； and

a third terminal and a terminal tab extending substantially perpendicular from the main body, wherein the third terminal is in physical contact with the spring element when the thermal linking material is below the melting point.
The TPV device of claim 8, the housing of the terminal assembly further comprising:

a buttress extending from an inner surface of the base, the buttress extending around the opening in the base and the third terminal of the inner electrode； and

a capping wall extending from the inner surface of the base, the capping wall receiving the terminal tab of the inner electrode.
The TPV device of claim 1, wherein the base of the housing of the terminal assembly includes a guide area recessed into the base, and wherein the guide area the first end of the spring element when the spring element disconnects from the thermal electrode.
The TPV device of claim 2, wherein sidewall of the housing engages the housing cover using a set of fasteners.
The TPV device of claim 1, wherein the first end of the spring element includes a protrusion extending outwardly, and wherein the thermal linking material is provided adjacent the protrusion on the spring element.
A thermally protected varistor (TPV) device, comprising:

a varistor body, comprising:

an electrode disposed along 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 electrode and a second lead is electrically connected to the thermal electrode； and

a terminal assembly coupled to the varistor body, the terminal assembly comprising:

a housing including a sidewall and a base, wherein an opening is provided in the base for electrical connection with the thermal electrode； and

a spring element having a first end disposed within the housing and a second end extending outside of the housing through a slot in the sidewall, the first end being connectable with the thermal electrode through the opening of the base to maintain the spring element in physical contact with the thermal electrode via a thermal linking material when the thermal linking material is below a thermal threshold, and

wherein a second terminal at the second end is connected to a third lead.
The TPV device of claim 13, the terminal assembly further comprising a housing cover coupled to at least one of: the housing, and the varistor body.
The TPV device of claim 13, wherein the thermal linking material melts and flows above the thermal threshold to create an insulating gap between the thermal electrode and the first end of the spring element.
The TPV device of claim 13, the housing of the terminal assembly further comprising:

a set of support walls defining a channel receiving the spring element； and

a support post adjacent the set of support walls, wherein the spring element bends at least partially around the support post.
The TPV device of claim 13, wherein the thermal linking material is a low-temperature solder disposed on a surface of the first end of the spring element.
The TPV device of claim 13, the terminal assembly further comprising a terminal clip coupling the varistor body with the housing.
The TPV device of claim 13, the terminal assembly further comprising an inner electrode disposed between the thermal electrode and the housing, the inner electrode comprising:

a main body； and

a third terminal and a terminal tab extending substantially perpendicular from the main body, wherein the third terminal is in physical contact with the spring element when thermal linking material is below the thermal threshold.
The TPV device of claim 19, the housing of the terminal assembly further comprising:

a buttress extending from an inner surface of the base, the buttress extending around the opening in the base and the third terminal of the inner electrode； and

a capping wall extending from the inner surface of the base, the capping wall receiving the terminal tab of the inner electrode.
The TPV device of claim 1, wherein the first end of the spring element includes a protrusion extending outwardly, and wherein the thermal linking material is provided adjacent the protrusion.