Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Patent
1996-08-26
1998-03-10
Tso, Edward
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
H01C 710, H01C 713
Patent
active
057266239
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an electrical component the resistance of which varies with temperature, and more particularly to a thermistor having a positive temperature coefficient (such that its resistance increases with temperature).
In many uses, thermistors carry heavy electrical currents and generate considerable heat. This heat must be dissipated in a controlled and reliable manner.
We have now devised a thermistor which can be surface-mounted to a substrate, such that it occupies relatively little space but allowing controlled dissipation of heat.
SUMMARY OF THE INVENTION
In accordance with this invention as seen from one aspect, there is provided a temperature dependent resistive component comprising opposite contact faces and two supports attached to the respective contact faces, each support having at least one projecting leg which terminates in a contact pad, the contact pads of the two supports lying in a common plane spaced from the component, for mounting to a substrate.
Preferably the component comprise a flat, disc-shaped element. In one embodiment, the two supports comprise two wires bonded to the disc across two angularly-spaced diameters thereof. Preferably the opposite ends of each wire project and are flattened to form contact pads.
In another embodiment, each support comprises a piece of sheet metal bonded to the respective face of the disc and provided with the projecting leg which terminates in the respective contact pad. Preferably the support is bonded to the respective side of the disc via one or more edges of the piece of sheet metal. Preferably the contact pad comprises a portion of the sheet metal, bent to lie in the required plane. Preferably each support comprises a piece of sheet metal bent into a channel-section, the two edges of the channel-section being bonded to the respective face of the disc.
In accordance with this invention as seen from a second aspect, there is provided a temperature dependent resistive component comprising opposite contact faces and two supports attached to the respective contact faces, each support having at least one projecting leg which terminates in a contact pad, with respective contact pads of the two supports lying in a common plane spaced outwardly from said component, for mounting the component to a substrate, at least one support comprising a piece of sheet metal bent into a channel-section and having the two edges of the channel-section bonded to the respective face of said component.
The component is preferably a PTC thermistor and is arranged to be mounted such that its underside lies either parallel or perpendicular to the substrate, but spaced by a small gap from the substrate. The dissipation of heat from the thermistor depends upon the surface area, cross-sectional area, contact pad area and material of the supports, and also the distance between the thermistor and the substrate. These parameters can be selected, in the design of the thermistor, to suit the heat dissipation requirements of particular applications.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
Embodiments of this invention will now be described by way of examples only and with reference to the accompanying drawing, in which:
FIG. 1 is a perspective view of one embodiment of PTC thermistor in accordance with the invention;
FIG. 2 is a side view of a second embodiment of PTC thermistor in accordance with the invention;
FIG. 3 is a view of the thermistor of FIG. 2 from one end;
FIG. 4 is a view of the thermistor of FIG. 2 from the opposite end;
FIG. 5 is a plan view of the thermistor of FIG. 2;
FIG. 6 is a side view of a third embodiment of thermistor in accordance with the invention;
FIG. 7 is a view of the thermistor of FIG. 6 from one edge;
FIG. 8 is a top view of the thermistor of FIG. 6; and
FIG. 9 is a bottom view of the thermistor of FIG. 6.
DETAILED DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENTS
Referring to FIG. 1 of the drawings, there is shown a disc-shaped thermistor 10 having a positive temperature coefficient (
REFERENCES:
patent: 5351026 (1994-09-01), Kanbara et al.
patent: 5446623 (1995-08-01), Kanetake
Bowthorpe Components Limited
Schindler Edward D.
Tso Edward
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