Thermally protected metal oxide varistor
First Claim
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1. A metal oxide varistor comprising:
- a varistor body;
a plurality of electrodes on the varistor body, at least one electrode being a fused electrode;
a plurality of leads; and
a fuse connecting at least one of the plurality of leads to the fused electrode, the fuse including an insulator overlying part of the fused electrode, a link having a portion overlying the insulator and a portion electrically connected to the fused electrode, the link being of a material having a melting point at or below a thermal safety temperature threshold for the varistor, and a body of hot melt material in contact with the link, the hot melt material being an electrical insulator and having a melting point such that it melts and flows to create an insulating gap between the fused electrode and the material of the link when the link becomes molten.
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Abstract
A varistor has a thermal fuse between a lead and an electrode. The fuse includes a link extending between the surface of an insulator and the fused electrode. The electrical connection of the link and the electrode is maintained by a low temperature solder fillet. That part of the link between the electrode and the insulator is surrounded by hot melt electrically insulating material. Upon sustained over-voltage conditions, the link and the solder fillet melt, and an insulating gap is rapidly created by molten hot melt material.
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Citations
13 Claims
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1. A metal oxide varistor comprising:
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a varistor body;
a plurality of electrodes on the varistor body, at least one electrode being a fused electrode;
a plurality of leads; and
a fuse connecting at least one of the plurality of leads to the fused electrode, the fuse including an insulator overlying part of the fused electrode, a link having a portion overlying the insulator and a portion electrically connected to the fused electrode, the link being of a material having a melting point at or below a thermal safety temperature threshold for the varistor, and a body of hot melt material in contact with the link, the hot melt material being an electrical insulator and having a melting point such that it melts and flows to create an insulating gap between the fused electrode and the material of the link when the link becomes molten. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A metal oxide varistor comprising:
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a varistor body;
a plurality of electrodes on the varistor body, at least one electrode being a fused electrode;
a plurality of leads; and
a thermal fuse connecting one of the plurality of leads to the fused electrode, the fuse further including an insulator overlying part of the fused electrode and a link of elongate shape and having flux surrounded by solder material having a melting point at or below a thermal safety temperature threshold for the varistor, the link including a first portion in contact with the fused electrode, a second portion surrounded by a body of hot melt material, said hot melt material also being in contact with the fused electrode, and a third portion overlying the insulator and being connected to a lead, wherein said hot melt material is an electrical insulator and has a melting point such that it melts and flows to create an insulating gap between the fused electrode and the material of the link when the link becomes molten.
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12. A fuse integrated in a metal oxide varistor, wherein the varistor includes a varistor body, a plurality of electrodes with at least one electrode being a fused electrode, and a plurality of leads, the fuse connecting at least one lead to the fused electrode, the fuse comprising:
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an insulator overlying part of the fused electrode;
a link having a portion overlying the insulator and a portion electrically connected to the fused electrode, the link being of a material having a melting point at or below a thermal safety temperature threshold for the varistor; and
a body of hot melt material in contact with the link, the hot melt material being an electrical insulator and having a melting point such that it melts and flows to create an insulating gap between the fused electrode and the material of the link when the link becomes molten.
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13. A fuse integrated in a metal oxide varistor, wherein the varistor includes a varistor body, a plurality of electrodes with at least one electrode being a fused electrode, a plurality of leads, the fuse connecting at least one lead to the fused electrode, the fuse comprising:
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an insulator overlying part of the fused electrode; and
a link of elongate shape and including flux surrounded by solder material having a melting point at or below a thermal safety temperature threshold for the varistor, the link further including a first portion in contact with the fused electrode, a second portion surrounded by a body of hot melt material, said hot melt material also being in contact with the fused electrode, and a third portion overlying the insulator and being connected to a lead, wherein said hot melt material is an electrical insulator having a melting point such that it melts and flows to create an insulating gap between the fused electrode and the material of the link when the link becomes molten.
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Specification