Reflowable thermal fuse

• US 20100245027A1
• Filed: 03/24/2009
• Published: 09/30/2010
• Est. Priority Date: 03/24/2009
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Inventors: Vranicar, Anthony, Chen, Jianhua, Matthiesen, Martyn A.
• Granted Patent: US 8,289,122 B2
• Time in Patent Office: Days
• US Class Current: 337/297
• CPC Class Codes: H01H 2037/046 being soldered on the printed circuit to be protected
• CPC Class Codes: H01H 2037/763 the spring being a blade spring
• CPC Class Codes: H01H 37/761 with a fusible element forming part of the switched circuit H01H37/767 takes precedence
• CPC Class Codes: Y10T 29/49107 Fuse making

Abstract

A reflowable thermal fuse includes a positive-temperature-coefficient (PTC) device that defines a first end and a second end, a conduction element that defines a first end and a second end in electrical communication with the second end of the PTC device, and a restraining element that defines a first end in electrical communication with the first end of the PTC device and a second end, in electrical communication with a second end of the conduction element. The restraining element is adapted to prevent the conduction element from coming out of electrical communication with the PTC device in an installation state of the thermal fuse. During a fault condition, heat applied to the thermal fuse diverts current flowing between the first end of the PTC device and the second end of the conduction element to the restraining element, causing the restraining element to release the conduction element and activate the fuse.

Claims

1. A thermal fuse comprising:

a positive-temperature-coefficient (PTC) device that defines a first end and a second end;

a conduction element that defines a first end and a second end, the first end of the conduction element in electrical communication with the second end of the PTC device; and

a restraining element that defines a first end and a second end, the first end of the restraining element in electrical communication with the first end of the PTC device and the second end of the restraining element in electrical communication with the second end of the conduction element, the restraining element being adapted to prevent the conduction element from coming out of electrical communication with the PCT device in an installation state of the thermal fuse.

2. The thermal fuse according to claim 1, wherein during a high temperature fault condition, heat applied to the thermal fuse causes current flowing between the first end of the PTC device and the second end of the conduction element to be diverted to the restraining element, causing the restraining element to release the conduction element.

3. The thermal fuse according to claim 2, wherein after the restraining element releases the conduction element, the applied heat causes the conduction element to electrically open.

4. The thermal fuse according to claim 1, wherein during a high current fault condition, a fault current flowing into the thermal fuse causes current flowing between the first end of the PTC device and the second end of the conduction element to be diverted to the restraining element, causing the restraining element to release the conduction element, and the fault current causes the PTC device to generate heat that causes the conduction element to electrically open.

5. The thermal fuse according to claim 1, wherein the conduction element includes a sensor that releasably secures the conduction element into electrical communication with the second end of the PTC device.

6. The thermal fuse according to claim 5, wherein the sensor melts at about 200°

C.

7. The thermal fuse according to claim 6, wherein the conduction element includes a spring portion that is under tension.

8. The thermal fuse according to claim 1, further comprising a housing that comprises the PTC device, the conduction element, and the restraining element.

9. The thermal fuse according to claim 1, further comprising a plurality of mounting pads disposed at least partially outside of the housing that enable surface mounting the thermal fuse to a panel.

10. The thermal fuse according to claim 9, wherein the first end of the PTC device and the first end of the restraining element are in electrical communication with a first pad of the plurality of pads and the second end of the conduction element and the second end of the restraining element are in electrical communication with a second pad of the plurality of mounting pads.

11. The thermal fuse according to claim 1, wherein the PTC device, the conduction element, and the restraining element are mounted on a substrate.

12. A method for placing a thermal fuse on a panel, comprising:

providing a reflowable thermal fuse that includes;

a positive-temperature-coefficient (PTC) device that defines a first end and a second end;

a conduction element that defines a first end and a second end, the first end of the conduction element in electrical communication with the second end of the PTC device; and

a restraining element that defines a first end and a second end, the first end of the restraining element in electrical communication with the first end of the PTC device and the second end of the restraining element in electrical communication with the second end of the conduction element, the restraining element being adapted to prevent the conduction element from coming out of electrical communication with the PCT device in an installation state of the thermal fuse;

placing the reflowable thermal fuse on a panel that includes pads for soldering the surface mountable fuse to the panel; and

running the panel through a reflow oven so as to solder the surface mountable fuse to the panel.

13. The method according to claim 12, further comprising diverting current flowing between the first end of the PTC device and the second end of the conduction element to the restraining element during a fault condition to cause the restraining element to release the conduction element.

14. The method according to claim 13, further comprising electrically opening the conduction element in response to applied heat after the restraining element releases the conduction element.

15. The method according to claim 13, further comprising electrically opening the conduction element in response to heat generated by the PTC device.

16. The method according to claim 12, wherein the conduction element includes a sensor that releasably secures the conduction element into electrical communication with the second end of the PTC device.

17. The method according to claim 16, wherein the sensor melts at about 200°

C.

18. The method according to claim 16, wherein the conduction element includes a spring portion that is under tension.

19. The method according to claim 12, wherein the reflowable thermal fuse further comprises a housing that includes the PTC device, conduction element, and restraining element.

20. The method according to claim 12, wherein the PTC device, the conduction element, and the restraining element are mounted on a substrate.