Electricity: electrothermally or thermally actuated switches – Thermally actuated switches – With fusible – combustible or explosive material
Patent
1994-12-15
1997-02-04
Picard, Leo P.
Electricity: electrothermally or thermally actuated switches
Thermally actuated switches
With fusible, combustible or explosive material
337402, 337407, H01H 3776
Patent
active
056002955
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a thermal fuse for fixing on a circuit substrate in the form of a spring clip which comprises two contact locations, whereof at least one is a solder location for connection to corresponding circuit contacts of the substrate as well as at least one elastic spring arm as connecting section between the two contact locations. The invention is also directed to a method for the activation of such a thermal fuse.
Such fuses serve the purpose of protecting circuit parts against thermal overload and can be utilized in any desired circuits, for instance on printed circuit boards. The preferred area of employment of the thermal fuse of the invention, however, are film circuits.
In general, thermal fuses of the species initially cited are variously known and for various employments, for example from DE-B-15 15 624. In the fuse shown therein, the spring arm is pre-stressed into its working position when the fuse is built in. It must thus be retained in the pre-stressed position with a special device during soldering and until the soldered connection has cooled. Particularly given film circuits, this requires complicated manipulation and complicated devices.
In order to avoid soldering under tension, it has likewise already been proposed (DE-A-38 25 897 and DE-A-39 30 819) to support the spring arms of a U-shaped fuse clip in their prestressed position with applied support elements. No clamp or retainer devices are thus required during soldering; the support elements, however, must be removed or bent off after soldering in order to allow the tension of the spring arms to take effect. An object of the present invention is to enable an even simpler fashioning of a thermal fuse wherein neither a pre-stress mount during soldering nor a separate support element at the spring arms themselves are required.
SUMMARY OF THE INVENTION
Given a thermal fuse of the species initially cited, the object is inventively achieved in that the spring clip comprises a plastically deformable bending section in the region between the two contact locations, and in that the spacing between the two contact locations given a tension-free spring arm corresponds to the regular spacing of the circuit contacts of the substrate, and in that a tension can be produced in the spring clip by deforming the bending section, said tension striving to change the spacing between the two contact locations.
This thermal fuse, further, is inventively produced in such a way that the spring clip has its solder locations placed tension-free onto the solder contacts of the circuit substrate and is soldered, and in that a pre-stress directed to modifications of the spacing between the solder locations is produced by deformation of the bending section in the spring clip.
In the invention, thus, the pre-stress of the spring arm or of the spring arms is not undertaken until after soldering on the circuit substrate has been carried out. As a result thereof, the form of the spring clip is especially simple and economical in terms of manufacture as well as in terms of manipulation during soldering, since support elements also need not be applied and subsequently removed. The pre-stress event can be implemented in a simple way on the circuit substrate with simple bending punches and requires no more outlay than, example, the removal of the support element given the thermal fuse of DE-A-38 25 897.
Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention shall be set forth in greater detail below with reference to exemplary embodiments on the basis of the drawing. Shown are:
FIG. 1 illustrates a side elevation of an inventively fashioned thermal fuse, according to the present invention.
FIG. 2 illustrates a front elevation of the thermal fuse of FIG. 1. FIG. 3 illustrates the thermal fuse of FIG. 2 in three phases: soldered in an unstre
REFERENCES:
patent: 4135176 (1979-01-01), McVey et al.
patent: 5280262 (1994-01-01), Fischer
Gandhi Jayprakash N.
Picard Leo P.
Siemens Aktiengesellschaft
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