Flexible electric heating pad using PTC ceramic thermistor chip heating elements

Claim 1

A flexible electrical heating pad, comprising: first and second flexible, planar electrical conductor means extending substantially parallel to each other and spaced from each other for conveying electrical current and for conducting heat; heating means formed of variable electrical resistance heating material electrically connected between said first and second conductor means for producing heat when current flows therethrough, said variable resistance heating material substantially increasing in resistance when a temperature limit is reached to reduce the current flowing through said heating means so as to control the heat output of the heating pad, said heating means including a plurality of chips of said variable resistance heating material, each of said chips having opposed planar surfaces in electrical and thermal contact with respective ones of said conductor means, said chips arranged in a two dimensional array, said total chip area being less than the total area of each of said conductor means, said chips being held in electrical and thermal contact with said conductor means by soldering, brazing, or welding; flexible, electrical insulating means disposed between those portions of said conductor means not contacted by said heating means for preventing contact between said first and second conductor means; flexible, electrical insulating material disposed externally of and covering the outer surfaces of said conductor means for preventing short circuit or shock by contact with said conductor means; wherein each of said conductor means comprises a substantially flat sheet of electrically and thermally conductive material having a planar thermal conductance greater than the planar thermal conductance of said electrical insulating means for preventing contact between said conductor means; and wherein said assembly including both said conductor means, said heating means and both said insulating means is bendable.