Patent Application
20090108980
The present disclosure relates, generally, to fuses. More particularly, it relates to fuses providing both thermal and overcurrent protection in a single fuse.
In many applications it is desirable to have multiple types of fuses, so that, for example, the fuse will open if it exceeds a predetermined current or if it reaches a predetermined temperature. In the case of a short circuit, an overcurrent fuse will open if the current exceeds a predetermined value. In the case of a “soft short”, where the current exceeds a normal operating value but is not high enough to open the overcurrent fuse, the thermal fuse will open if one or more components in the circuitry in proximity to the fuse becomes too hot. In many applications, particularly electronic devices, it would be desirable to combine the overcurrent protection and thermal protection in a single device to minimize the required space.
In various aspects, the present disclosure includes a fuse providing both overcurrent protection and thermal protection in a single fuse. In particular, at least a portion of the fuse may include a material with a predetermined melting point to provide thermal protection.
In one aspect, a fuse includes first and second leads. A fuse element provides electrical communication between the first and second leads. The fuse element includes a material with a melting point of less than 250° C. and acts as both an overcurrent fuse and a thermal fuse by melting when subjected to a predetermined current or upon reaching a predetermined temperature. A body houses the fuse element and portions of the first and second leads.
In another aspect, a fuse includes first and second leads. An electrically insulating structure is disposed between the first and second leads. A wire is wrapped around the electrically insulating structure and provides electrical communication between the first and second leads. The wire acts as both an overcurrent fuse and a thermal fuse by melting when subjected to a predetermined current or upon reaching a predetermined temperature. A body houses the electrically insulating structure, the wire, and portions of the first and second leads.
In another aspect, a fuse includes first and second leads. A rod is disposed between the first and second leads. The rod includes an electrically insulating core portion and an electrically conducting coating portion. The electrically conducting coating portion provides electrical communication between the first and second leads. The electrically conducting coating portion acts as both an overcurrent fuse and a thermal fuse by melting when subjected to a predetermined current or upon reaching a predetermined temperature. A body houses the rod and portions of the first and second leads.
The fuse element, wire, conductive coating or low melting temperature lead can be made of a material, such as tin, SnIn52, SnZn9, SnCu0.7 and indium. The predetermined current can be 50 mA to 10 A, for example. The leads of the various embodiments are attached mechanically to the fuse element or rod in one embodiment.
In another aspect, a fuse includes first and second leads. At least a portion of one of the first and second leads includes a material with a melting point of less than 250° C. The portion acts as a thermal fuse by melting upon reaching a predetermined temperature. A fuse element provides electrical communication between the first and second leads. The fuse element acts as an overcurrent fuse by melting when subjected to a predetermined current. A body houses the fuse element and portions of the first and second leads.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.
Referring now to the drawings and, in particular, to
A fuse element 50 is in electrical communication with the ends 21, 25 of leads 20, 22. The fuse element 50 may be generally rod or cylindrically shaped, but other shapes are possible. A typical dimension for fuse element 50 is five mm in length and 0.2 mm in diameter. The fuse element 50 in one embodiment is comprised of a material with a melting point of less than 250° C. The fuse element 50 acts as both an overcurrent fuse and a thermal fuse by melting when subjected to either a predetermined current or upon reaching a predetermined temperature. The predetermined current may be about 120 mA. Other possible predetermined current values may be in the range of 50 mA to 10 A. The predetermined current is determined by the resistance and melting temperature of the fuse element 50 and thus depends on the material, size and shape of the element 50.
The predetermined melting temperature may be about 157° C. The predetermined temperature is primarily dependent on the melting point of the fuse element 50, although the size and shape of the fuse element 50 may determine the time it takes for the element 50 to melt. The predetermined melting temperature may be a variety of desired levels, including less than 250° C., less than 225° C., less than 200° C., and less than 175° C. In one embodiment, the fuse element 50 is made of indium to provide a melting temperature of about 157° C. Alternatively, fuse element 50 could be made of tin to provide a melting temperature of about 232° C. Various alloys could also be used for fuse element 50, for example SnIn52, SnZn9 or SnCu0.7 with melting temperatures of about 118° C., 199° C. and 227° C., respectively.
The fuse element 50 may be mechanically connected to leads 20, 22 by fingers 24. Mechanical connection may be preferable to soldering in many applications to avoid melting the fuse element 50. The fingers 24 may bend or be crimped around the fuse element 50 to secure the element 50 adjacent the ends 21, 25 of leads 20, 22. Other methods of attaching fuse element 50 to leads 20, 22 are possible, such as electrically conductive adhesive. Fingers 24 may be integrally formed with leads 20, 22, or alternatively mechanically attached thereto, such as by soldering or welding. Leads 20, 22 may have swaged or flattened portions 26 adjacent ends 23, 27. Flattened portions 26 allow the fuse 10 to be press fit through a hole in a substrate, such as a circuit board. This is particularly useful in embodiments where fuse element 50 includes a low melting point material, in that it would be difficult to solder such a fuse to a substrate or printed circuit board without melting the fuse element 50.
Fuse 10 may be construed in a similar manner as a conventional fuse, with care taken to avoid subjecting the fuse element 50 to a temperature near its melting point. The fuse 10 may be constructed by first providing leads 20, 22 of the appropriate shape and size. Base 30 is then molded around the leads 20, 22. Alternatively, base 30 may be cast around the leads 20, 22. Fuse element 50 is then connected to leads 20, 22 by bending or crimping fingers 24 around the fuse element 50. A cover 50 is then inserted around the fuse element 50 and secured to the base 30. Prior to inserting cover 50, it may be partially or completely filled with an arc suppressing material such as silica sand or ceramic powder to enhance the current and voltage interrupting properties of the fuse.
In operation, current flows between leads 20, 22 and through fuse element 50. If the current exceeds a predetermined value, the resistance in fuse element 50 causes the element 50 to heat up and melt, thus breaking the circuit between leads 20 and 22. Likewise, if a current fault provides an increased current that is less than the predetermined overcurrent condition but causes one or more components in the circuitry in proximity to the fuse to overheat, fuse element 50 will melt, thus breaking the circuit.
A second embodiment of a fuse 12 is shown in
Like fuse 10, the fuse element 60 of fuse 12 provides both overcurrent and thermal protection. Wire 64 will melt when subjected to either a predetermined current or upon reaching a predetermined temperature. The predetermined temperature is primarily dependent on the melting point of the material of wire 64, although the size and shape of the wire 64 may determine the time it takes for the wire to melt. Wire 64 may be comprised of indium or any of the other previously mentioned alloys. Typical dimensions for wire 64 are five mm in total length and 0.2 mm in diameter, with a suitable number of total turns. The predetermined melting temperature may be any of the previously described melting temperatures for fuse 10. Fuse 12 may be constructed in a manner similar to conventional fuses.
A third embodiment of a fuse 14 is shown in
Like fuses 10 and 12, the rod element 70 of fuse 12 provides both overcurrent and thermal protection. The electrically conducting coating portion 74 acts as both an overcurrent fuse and a thermal fuse by melting away from the insulating core portion 72 when subjected to either a predetermined current or upon reaching a predetermined temperature, thus breaking the circuit between leads 20 and 22. The predetermined temperature is primarily dependent on the melting point of the material of coating portion 74, although the thickness and shape of the coating portion 74 may determine the time it takes for it to melt. The predetermined melting temperature may be any one of the previously described temperature levels. Coating portion 74 may be comprised of indium or any of the other previously mentioned alloys. Insulating core portion 72 may be comprised of any suitable insulating material, such as silicone or ceramic yarn. Typical dimensions for rod 70 are 5 mm in total length and 0.2 mm in diameter. Rod element 70 is connected to leads 20 and 22 as described herein.
A fourth embodiment of a fuse 16 is shown in
Fuse 16 may be constructed in much the same manner as a conventional fuse. However, since portion 38 includes a low-melting point material, the use of soldering may be limited in order to avoid melting the low-melting point material. Other methods of connection, such as conductive adhesives (e.g. conductive epoxies or silicones), may be used instead. Additionally, if either of the leads 32, 36 includes a low-melting point material, it is preferred that the base 30 be cast instead of molded to avoid undesirable melting of the leads.
It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/978,580, filed Oct. 9, 2007, having the same title as above.
| Number | Date | Country | |
|---|---|---|---|
| 60978580 | Oct 2007 | US |
