Electrically activated surface mount thermal fuse

• US 8,581,686 B2
• Filed: 03/24/2009
• Issued: 11/12/2013
• Est. Priority Date: 03/24/2009
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Inventors: Galla, Matthew P., Chen, Jianhua, Mattheisen, Martyn A.
• Primary Examiner(s): THOMAS, BRADLEY H
• Application Number:
  US12/383,595
• Publication Number:
  US 20100245022A1
• Time in Patent Office: 1,694 Days
• Field of Search: 337/231, 337/409, 337/148, 337/314, 337/315, 337/317, 337/388
• US Class Current: 337/409
• CPC Class Codes: H01H 2037/046 being soldered on the printed circuit to be protected
• CPC Class Codes: H01H 2037/762 using a spring for opening the circuit when the fusible element melts
• 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 conduction element with first and second ends, disposed within a housing. The reflowable thermal fuse also includes an elastic element disposed within the housing and adapted to apply force on the conduction element in an activated state of the reflowable thermal fuse. A restraining element is utilized to secure the elastic element and prevent the elastic element from applying force on the conduction element in an installation state of the reflowable thermal fuse. Application of an activating current through the restraining element causes the restraining element to break and thereby release the elastic element and place the reflowable thermal fuse in the activated state.

Claims

1. A reflowable, surface-mountable thermal fuse comprising:

a conduction element with first and second ends;

a sensor in mechanical communication with the conduction element;

an elastic element adapted to apply force on the conduction element in an activated state of the thermal fuse;

a plurality of mounting pads that enable surface mounting the thermal fuse; and

a restraining element adapted to secure the elastic element and thereby prevent the elastic element from applying force on the conduction element in an installation state of the thermal fuse, wherein application of an activating current through the restraining element causes the restraining element to break and thereby release the elastic element and place the thermal fuse in the activated state without severing the conduction element, allowing opening of the conduction element during a subsequent fault condition.

2. The thermal fuse according to claim 1, wherein when an ambient temperature around the thermal fuse exceeds a threshold, the sensor loses resilience and becomes subject to deformation and allows the conduction element to open under the force applied by the elastic element.

3. The thermal fuse according to claim 1, wherein the sensor comprises solder.

4. The thermal fuse according to claim 1, wherein the elastic element corresponds to a spring.

5. The thermal fuse according to claim 4, wherein the spring corresponds to a coil spring.

6. The thermal fuse according to claim 4, wherein the spring corresponds to a leaf spring.

7. The thermal fuse according to claim 1, wherein the elastic element comprises an electrically conductive material.

8. The thermal fuse according to claim 1, wherein a tip of the elastic element is tapered so as to concentrate the force applied by the elastic element in the tip.

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

10. The thermal fuse according to claim 9, wherein the first and second ends of the conduction element are in electrical communication with first and second mounting pads of the plurality of mounting pads.

11. The thermal fuse according to claim 10, wherein the restraining element includes first and second ends that are in electrical communication with third and forth mounting pads of the plurality of mounting pads.

12. The thermal fuse according to claim 10, wherein the restraining element includes a first end that is in electrical communication with at least one of the first and second mounting pads, and a second end that is in electrical communication with a third pad of the plurality of mounting pads.

13. The thermal fuse according to claim 10, wherein the restraining element includes first and second ends that are in electrical communication with the first and the second mounting pads, respectively, of the plurality of mounting pads.

14. The thermal fuse according to claim 1, wherein the restraining element comprises a first region adapted to open when the activating current flows through the restraining element and a second region adapted to not open when the activating current flows through the restraining element.

15. A reflowable, surface-mountable thermal fuse comprising:

a conduction element comprising an outer tube with first and second ends;

a sensor in mechanical communication with the conduction element, said sensor being contained by the outer tube which is adapted to contain the sensor when the sensor loses resilience and melts;

an elastic element adapted to apply force on the conduction element in an activated state of the thermal fuse;

a plurality of mounting pads that enable surface mounting the thermal fuse; and

a restraining element adapted to secure the elastic element and thereby prevent the elastic element from applying force on the conduction element in an installation state of the thermal fuse,

wherein application of an activating current through the restraining element causes the restraining element to break and thereby release the elastic element and place the thermal fuse in the activated state without severing the conduction element; and

wherein under a fault condition causing the sensor to lose resilience and melt, force applied by the elastic element causes an opening to form in the sensor to prevent current from flowing through the sensor.

16. A reflowable, surface-mountable thermal fuse comprising:

a conduction element with first and second ends;

a sensor in mechanical communication with the conduction element;

a heat producing device in electrical communication with the sensor adapted to generate heat during a fault condition, the generated heat causing the sensor to lose resilience;

an elastic element adapted to apply force on the conduction element in an activated state of the thermal fuse;

a plurality of mounting pads that enable surface mounting the thermal fuse; and

a restraining element adapted to secure the elastic element and thereby prevent the elastic element from applying force on the conduction element in an installation state of the thermal fuse, wherein application of an activating current through the restraining element causes the restraining element to break and thereby release the elastic element and place the thermal fuse in the activated state without severing the conduction element, allowing opening of the conduction element during a subsequent fault condition.

17. The thermal fuse according to claim 16, wherein the heat producing device corresponds to a positive-temperature-coefficient (PTC) device.

18. The thermal fuse according to claim 16, wherein the restraining element comprises a first region adapted to open when the activating current flows through the restraining element and a second region adapted to not open when the activating current flows through the restraining element.

19. A reflowable, surface-mountable thermal fuse comprising:

a housing with a plurality of pads that enable mounting the thermal fuse via a surface mount technique;

first, second, and third pads of the plurality of pads disposed at least partially outside of the housing;

a conduction element with first and second ends, disposed within the housing and in electrical communication with the first and second pads;

an elastic element disposed within the housing and adapted to apply force on the conduction element in an activated state of the thermal fuse; and

a restraining element with a first end in electrical communication with the first pad and a second end in electrical communication with the third pad, wherein the restraining element is adapted to secure the elastic element and thereby prevent the elastic element from applying force on the conduction element in an installation state of the thermal fuse, and wherein application of an activating current through the first pad to the third pad causes the restraining element to break and thereby release the elastic element and place the thermal fuse in the activated state without severing the conduction element, allowing opening of the conduction element during a subsequent fault condition.

20. The thermal fuse according to claim 19, wherein when an ambient temperature around the thermal fuse exceeds a threshold, the sensor loses resilience and becomes susceptible to deformation and the conduction element opens under the force applied by the elastic element.