CN116073349A

CN116073349A - Thermal protection metal oxide varistor

Info

Publication number: CN116073349A
Application number: CN202111271664.8A
Authority: CN
Inventors: 闵龙; 宋东健
Original assignee: Dongguan Littelfuse Electronic Co Ltd
Current assignee: Dongguan Littelfuse Electronic Co Ltd
Priority date: 2021-10-29
Filing date: 2021-10-29
Publication date: 2023-05-05

Abstract

The application discloses a thermally protected metal oxide varistor. A method of creating an opening through a Metal Oxide Varistor (MOV) coating is disclosed. In some embodiments, an assembly may include a cutting device including a cutting apparatus, a rotatable platform adjacent the cutting device, and a plurality of Metal Oxide Varistors (MOVs) coupled to the rotatable platform, wherein the cutting apparatus may be biased toward the rotatable platform to form openings in a coating formed on each of the plurality of MOVs.

Description

Thermal protection metal oxide varistor

Technical Field

Embodiments relate to the field of circuit protection devices, and more particularly, to an apparatus and method for thermally protecting a metal oxide varistor.

Background

Overvoltage protection devices are used to protect electronic circuits and components from damage due to overvoltage fault conditions. These overvoltage protection devices may include a Metal Oxide Varistor (MOV) connected between the circuit to be protected and ground. MOVs have current-voltage characteristics that allow them to be used to protect such circuits from catastrophic voltage surges. MOVs are typically composed of a ceramic disc, often based on ZnO, an electrical contact layer acting as an electrode, such as an Ag (silver) electrode, and a first and a second metal lead connected at a first and a second surface, respectively, wherein the second surface is opposite to the first surface.

A thermally protected MOV (TMOV) can form an open circuit just before the MOV fails due to catastrophic overheating under overvoltage conditions. Continuous current leakage from the line to the neutral point increases MOV damage and MOV power consumption before triggering the thermal fuse (TCO). MOVs integrated with Gas Discharge Tubes (GDTs) have no thermal fuses and therefore cannot be opened in time to prevent combustion when sustained abnormal overvoltage occurs.

It is with respect to this and other deficiencies of the prior art that the present disclosure is provided.

Disclosure of Invention

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one method, a protective device may include a varistor body having a first side opposite a second side, a Gas Discharge Tube (GDT) coupled to the first side, and a first lead connected to the GDT by a fusible element and a second lead connected to the second side.

In another approach, a circuit protection assembly may include a varistor body having a first side opposite a second side, a Gas Discharge Tube (GDT) coupled to the first side, and a first lead connected to the GDT by a fusible element and a second lead connected to the second side. The circuit protection assembly may further include an insulating member coupled to the first side, wherein the fusible element extends over the insulating member.

In yet another method, a circuit protection assembly may include a varistor body having a first side opposite a second side, a Gas Discharge Tube (GDT) coupled directly to the metallization layer along the first side, and a first lead connected to the GDT by a fusible element and a second lead connected to the second side, the circuit protection assembly may further include an insulating member coupled to the first side, wherein the first lead terminates above the insulating member.

Drawings

The drawings illustrate exemplary methods of the disclosed embodiments heretofore devised for practical application of the principles thereof, wherein:

FIG. 1 is a perspective view of an assembly according to an embodiment of the present disclosure; and

FIG. 2 is a rear view of the assembly of FIG. 1, according to an embodiment of the present disclosure;

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

Moreover, some elements in some of the figures may be omitted or not shown to scale for clarity of illustration. For clarity of illustration, the cross-sectional view may be in the form of a "slice" or "near" cross-sectional view, omitting certain background lines that would otherwise be visible in the "true" cross-sectional view. In addition, some reference numerals may be omitted in some of the drawings for clarity.

Detailed Description

An assembly, apparatus, and method according to the present disclosure will be described more fully below with reference to the accompanying drawings, in which embodiments are shown. The components, devices, and methods may 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 be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

As will be described in more detail herein, embodiments of the present disclosure provide a Metal Oxide Varistor (MOV) with extended life thermal protection and no leakage current. By providing a Gas Discharge Tube (GDT) in series with the hot MOV, almost zero leakage current will flow through the whole device. In some embodiments, a flat circular GDT may be attached to the metallization layer of the MOV to form a series connection. The first lead may be soldered to one side of the MOV. The second lead may be connected to an isolator member coupled to the metallization layer. In some embodiments, the separator component is an alumina separator. The second lead may be connected to the first end of the low melting point welding wire. The second end of the wire is connected to the GDT. In some embodiments, a small recess on the electrode of the GDT provides a region to collect molten wire when a thermal cutoff event occurs, thereby preventing the MOV disk from shorting.

As will be described herein, embodiments of the present disclosure provide at least the following advantages: (1) Zero standby energy consumption, no leakage and longer service life; (2) The GDT isolates the MOV from the line voltage, enabling the low rated MOV to be applied to high voltage circuits above the MOV's Maximum Continuous Operating Voltage (MCOV) rating; (3) Lowering the clamp voltage by allowing the use of lower rated MOV discs; (4) lower capacitance enables communication circuit applications; (5) no leakage current characteristics to enable DC circuit applications; (6) if the MOV is overheated, the low melting point wire will cut the circuit; (7) The recess or groove on the GDT electrode will prevent soft solder from reaching the metallization layer of the MOV and causing a short circuit; (8) implementing a DC circuit application with no leakage current characteristics; and (9) if the GMOV overheats, the low melting point wire will cut the circuit.

Turning to fig. 1-2, a circuit protection device or assembly 100 according to the present embodiment will be described. The assembly 100 may include a varistor body 102 with a first side 104 opposite a second side 106. Although non-limiting, the varistor body 102 may be part of a thermal metal oxide varistor that includes a first metallization layer (e.g., electrode) 108 along the first side 104 and a second metallization layer (e.g., electrode) 110 along the second side 106. The first and

second metallization layers

108, 110 may include one or more layers of silver, copper, aluminum, and/or copper plus aluminum.

The first lead 112 may extend along the first side 104 and the second lead 114 may extend along the second side 106. The first and second leads 112, 114 facilitate electrical connection of the component 100 within the circuit. In various non-limiting embodiments, the second lead may be electrically connected to the second metallization layer 110 via soldering, welding, conductive adhesive, or the like. Although not shown, the varistor body 102 may be encased or surrounded by a conformal epoxy or other highly insulating material.

The varistor body 102 may be formed of any MOV composition known in the art including, but not limited to, zinc oxide particles embedded in ceramic. The varistor body 102 and the first and

second metallization layers

108, 110 are depicted as circular, but this is not critical. It is contemplated that one or more of the varistor body 102, the first metallization layer 108, and the second metallization layer 110 may have different shapes, such as rectangular, triangular, irregular, etc., without departing from the scope of the present disclosure.

As further shown, the assembly 100 may include a Gas Discharge Tube (GDT) 120 coupled to the first metallization layer 108 along the first side 104. In some embodiments, the GDT 120 may include a center tube 121 sandwiched between a first electrode 122 and a second electrode 124. As shown, the second electrode 124 may be in direct physical contact with the first metallization layer 108. In some embodiments, the GDT 120 may be soldered to the first metallization layer 108 to provide a series electrical connection therebetween.

As shown, the first electrode 122 may include a central protrusion 126 operable to connect with a fusible element (e.g., wire) 130, an outer ring 132, and a recess 134 between the central protrusion 126 and the outer ring 132. Recess 134 provides fusible element 130 with a cavity or region that is movable upon melting (e.g., during a continuous abnormal overcurrent event). In some embodiments, the recess 134 is cylindrical or annular in shape and extends around the central protrusion 126. In other embodiments, the recess 134 may take on different shapes and/or configurations. As further shown, the outer ring 132 extends around the recess 134. Advantageously, shorting is avoided by preventing soft solder from the fusible element 130 from reaching the second electrode 124 and the first metallization layer 108 by means of the recess 134 and the outer ring 132. In some embodiments, the plane defined by the upper surface of the outer ring 132 is coplanar with the upper surface of the central protrusion 126. In other embodiments, the central protrusion 126 extends above a plane defined by the upper surface of the outer ring 132. Further, the plane defined by the recess 134 may be different from the plane defined by the central protrusion and/or the upper surface of the outer ring 132. Embodiments herein are not limited in this context.

The assembly 100 may also include an insulating member 140 coupled to the first metallization layer 108 along the first side 104. In some embodiments, insulating member 140 may be an alumina isolator including an upper surface 142 and a lower surface 144, wherein lower surface 144 is directly connected to first metallization layer 108 in a region directly adjacent to GDT 120. Although shown as a disc, it should be understood that the insulating member 140 may take on a variety of shapes in alternative embodiments. Further, it should be appreciated that insulating member 140 may be formed from a variety of different electrically insulating materials, including but not limited to ceramic materials.

As shown, a first end 144 of the fusible element 130 may be connected to the GDT 120 and a second end 146 of the fusible element 130 may be connected to the first lead 112, e.g., along the upper surface 142 of the insulating member 140. More specifically, the first end 144 of the fusible element 130 may be in direct physical contact with the central protrusion, while the second end 146 of the fusible element 130 may be in direct physical contact with the free end 150 of the first lead 112. Although not limited, the fusible element 130 may include one or more bends or varieties (ties) 152 in the event that there is a height differential between the upper surface 142 of the insulating member 140 and the central protrusion 126 and/or the outer ring 132. It should be appreciated that in other embodiments, the height of the upper surface 142 of the insulating member 140 may be the same as the height of the central protrusion 126 and/or the outer ring 132.

In summary, embodiments of the present disclosure provide a thermally protected GMOV in which a flat circular GDT is soldered onto an MOV metallization layer to form a series connection. One wire is soldered to the side of the MOV without the GDT. The other wire is insulated from the MOV disc by a circular alumina wafer. The lead is connected to one end of a low melting point welding wire. The opposite end of the wire is connected to the GDT. A small recess on the GDT electrode will contain soft solder to prevent shorting of the MOV disk in the event of a continuous abnormal overvoltage.

As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural elements or steps, 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.

The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Thus, the terms "comprising," "including," or "having," and variations thereof, are open-ended and are used interchangeably herein.

The phrases "at least one," "one or more," and/or "as used herein are open-ended expressions and are both conjunctive and disjunctive in operation. For example, the expressions "at least one of A, B and C", "at least one of A, B or C", "one or more of A, B and C", "one or more of A, B or C" and "A, B and/or C" refer to a alone, B alone, C, A and B together, a and C together, B and C together, or A, B and C together.

All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, rear, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, and counterclockwise) are used for identification purposes only to aid the reader's understanding of the present disclosure. The directional references do not impose limitations, particularly with respect to position, orientation, or use of the present disclosure. Joinder references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. Thus, a connective reference does not necessarily infer that two elements are directly connected and in fixed relation to each other.

Moreover, identifying references (e.g., primary, secondary, first, second, third, fourth, etc.) are not intended to imply importance or priority, but rather are used to distinguish one feature from another. The drawings are for illustrative purposes only and the dimensions, positions, sequences and relative sizes reflected in the drawings herein may vary.

Furthermore, the terms "substantially" or "approximately" and the terms "approximately" or "approximately" may be used interchangeably in some embodiments and may be described using any relative metric acceptable to one of ordinary skill in the art. For example, these terms may be used as a comparison to a reference parameter to indicate a deviation that can provide the intended function. Although non-limiting, deviations from the reference parameter may be, for example, within amounts of less than 1%, less than 3%, less than 5%, less than 10%, less than 15%, less than 20%, etc.

Although specific embodiments of the disclosure have been described herein, the disclosure is not so limited, as the scope of the disclosure is to be permitted in the art, and the specification can be read likewise. Accordingly, the above description should not be construed as limiting. Rather, the foregoing description is intended as examples of specific embodiments only. Other modifications within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art.

Claims

1. A protection device, comprising:

a varistor body having a first side opposite a second side;

a Gas Discharge Tube (GDT) coupled to the first side; and

a first lead connected to the GDT through a fusible element and a second lead connected to the second side.

2. The protective apparatus of claim 1, further comprising an insulating member coupled to the first side.

3. The protective apparatus of claim 2, wherein the first lead terminates along a surface of the insulating member.

4. A protection device according to claim 3, wherein a first end of the fusible element is connected to the GDT, and wherein a second end of the fusible element is connected to the first lead along a surface of the insulating component.

5. The protection device of claim 2, wherein the insulating component is an aluminum oxide wafer.

6. The protection device of claim 2, wherein the insulating member is directly adjacent to the GDT.

7. The protection device of claim 1, wherein the first side of the varistor body comprises a metallization layer, and wherein the GDT is welded to the metallization layer.

8. The protective apparatus of claim 7, wherein the GDT comprises a first electrode in direct contact with the fusible element and a second electrode in direct contact with the metallization layer.

9. The protective apparatus of claim 8, wherein the first electrode comprises:

an outer ring extending around the outer periphery; and

a recessed region adjacent to the outer ring, wherein the recessed region is operable to collect the fusible element as the fusible element melts.

10. The protective device of claim 1, wherein the varistor body is a thermal metal oxide varistor body, and wherein the fusible element is a wire.

11. A circuit protection assembly comprising:

a varistor body having a first side opposite a second side;

a Gas Discharge Tube (GDT) coupled to the first side;

a first lead connected to the GDT through a fusible element and a second lead connected to the second side; and

an insulating member coupled to the first side, wherein the fusible element extends over the insulating member.

12. The circuit protection assembly of claim 11 wherein said first lead terminates along a surface of said insulating member.

13. The circuit protection assembly of claim 12 wherein a first end of said fusible element is connected to said GDT, and wherein a second end of said fusible element is connected to said first lead in a region above said insulating member.

14. The circuit protection assembly of claim 11 wherein the insulating component is an aluminum oxide wafer, and wherein the aluminum oxide wafer is directly coupled to a metallization layer along a first side of the varistor body.

15. The circuit protection assembly of claim 14 wherein said GDT is soldered to said metallization layer.

16. The circuit protection assembly of claim 14 wherein said GDT comprises a first electrode in direct contact with said fusible element and a second electrode in direct contact with said metallization layer.

17. The circuit protection assembly of claim 16 wherein said first electrode comprises:

a central protrusion;

a recessed region surrounding the central protrusion, the recessed region being operable to collect the fusible element as the fusible element melts; and

an outer ring surrounding the recess region, wherein the recess region extends along a different plane than the outer ring and the central protrusion.

18. A circuit protection assembly comprising:

a varistor body having a first side opposite a second side;

a Gas Discharge Tube (GDT) directly coupled to the metallization layer along the first side;

an insulating member coupled to the first side, wherein the first lead terminates on the insulating member.

19. The circuit protection assembly of claim 18 wherein a first end of said fusible element is connected to said GDT, wherein a second end of said fusible element is connected to said first lead in an area above said insulating component, wherein said insulating component is an aluminum oxide wafer, and wherein said aluminum oxide wafer is directly coupled to said metallization layer.

20. The circuit protection assembly of claim 18 wherein said GDT comprises a first electrode in direct contact with said fusible element and a second electrode in direct contact with said metallization layer, and wherein said first electrode has a recessed area operable to collect said fusible element when said fusible element melts.