Insulated thermal cut-off device

Patent metadata

Field	Value
Publication number	US-9831054-B2
Application number	US-201414228196-A
Country	US
Kind code	B2
Filing date	Mar 27, 2014
Priority date	Mar 27, 2014
Publication date	Nov 28, 2017
Grant date	Nov 28, 2017

Abstract

A thermal cut-off device includes a plastic base, two electrodes, a temperature sensing element, and a plastic cover that fits over the base. The temperature sensing element is curved downward, and may be a bimetal or a trimetal. When the device is subject to an over-temperature condition, the orientation of the curve flips such that the temperature sensing element is then curved upward. When the temperature sensing element is curved upward, it lifts an arm of one of the electrodes, which severs the electrical connection between the electrodes. In this manner the device shuts off during an over-temperature condition in order to protect the circuit in which the device is installed. To prevent corrosion of the temperature sensing element, a first moisture insulation layer is applied to the outer surface of the thermal cut-off device. The moisture insulation layer may be an epoxy adhesive or a UV/visible light-cured adhesive or light/heat cured adhesive. In some embodiments, a second moisture insulation layer is formed on the surface of the temperature sensing element.

First claim

What is claimed is:

1. A thermal cut-off device comprising:
a base;
a first electrode positioned above the base and comprising a terminal portion;
a temperature sensing element positioned above a portion of the first electrode;
a second electrode positioned above the temperature sensing element and comprising a terminal portion;
a cover having edges that extend laterally and around edges of the base to form a structure that encloses the thermal sensing element, portions of the first and second electrodes, and at least a portion of the base such that the portion of the base is disposed within the cover, wherein the terminal portions of the first and second electrodes protrude from the structure formed by the cover and base; and
a first moisture insulation layer coated on at least a portion of an outer surface of the structure formed by the cover and base;
wherein the edges of the cover extend longitudinally to form a t-slot, and the base includes a t-shaped longitudinal portion of the base, such that the t-shaped longitudinal portion of the base is received into the longitudinal t-slot of the cover.

2. The thermal cut-off device of claim 1 , wherein the first moisture insulation layer comprises an epoxy adhesive.

3. The thermal cut-off device of claim 1 , wherein the first moisture insulation layer comprises an epoxy resin comprising a curing agent.

4. The thermal cut-off device of claim 3 , wherein the curing agent comprises polyoxypropylenediamine.

5. The thermal cut-off device of claim 1 , wherein the first moisture insulation layer comprises a light-curable adhesive.

6. The thermal cut-off device of claim 1 , wherein the first moisture insulation layer comprises a light and heat-curable adhesive.

7. The thermal cut-off device of claim 1 , where the temperature sensing element comprises two or more expansion layers.

8. The thermal cut-off device of claim 1 , wherein the temperature sensing element comprises a bimetal.

9. The thermal cut-off device of claim 1 , wherein the temperature sensing element comprises a trimetal.

10. The thermal cut-off device of claim 1 , wherein the temperature sensing element is curved such that a bottom surface of the temperature sensing element is a concave surface.

11. The thermal cut-off device of claim 10 , wherein the temperature sensing element is configured to flip the orientation of the curve when a temperature of the device exceeds a predetermined temperature such that after the device reaches the predetermined temperature, a top surface of the temperature sensing element becomes the concave surface.

12. The thermal cut-off device of claim 11 , wherein the temperature sensing element is configured to lift a portion of the second electrode when the orientation of the curve of the temperature sensing element flips upward such that an electrical connection between the first and second electrodes is severed.

13. The thermal cut-off device of claim 1 , further comprising a positive temperature coefficient (PTC) chip positioned below the temperature sensing element.

14. The thermal cut-off device of claim 1 , further comprising a second moisture insulation layer coated on the surface of the temperature sensing element.

15. The thermal cut-off device of claim 14 , wherein the second moisture insulation layer comprises a contact lubricant or a contact coating.

16. The thermal cut-off device of claim 14 , wherein the second moisture insulation layer provides a hydrophobic wax-based coating.

17. The thermal cut-off device of claim 14 , wherein the second moisture insulation layer provides an electrically penetrable thin coating.

18. The thermal cut-off device of claim 15 , wherein the second moisture insulation layer comprises a contact coating comprising a hydrophobic fluorinated polymer.

19. The thermal cut-off device of claim 1 , wherein the cover includes a frame portion having an opening, and an over-mold portion, the over-mold portion disposed in the opening of the frame.

20. The thermal cut-off device of claim 1 , wherein a frame portion of the cover surrounds each corner of the base.

Assignees

• Littelfuse Inc
• Littelfuse Japan G K

Inventors

• Chen Jianhua
• Guo Weiqing
• Ngo Minh V
• Hilty Robert D
• Tanaka Arata

Classifications

• H01H37/5427 Primary

  encapsulated in sealed miniaturised housing · CPC title

• H01H9/04

  Dustproof, splashproof, drip-proof, waterproof, or flameproof casings · CPC title

• H01H2037/528

  the bimetallic element being composed of more than two layers · CPC title

• H01H37/54

  wherein the bimetallic element is inherently snap acting · CPC title

• H01H37/52 Primary

  actuated due to deflection of bimetallic element · CPC title