Circuit protection devices

Claim 2

A circuit protection device whose largest dimension is less than 12 inches, which has a resistance at 23° C. of less than 100 ohms and which comprises (1) a conductive polymer element, at least a part of which is a PTC element, and (2) two electrodes, at least one of which has an electrically active surface of a generally columnar shape, and which can be connected to a source of electrical power and, when so connected, cause current to flow through said PTC element; said device being such that, if the portion thereof between the electrodes is divided into parallel-faced slices, the thickness of each slice being about 1/10 of the distance between the closest points of the two electrodes and the faces of the slices being planes which are perpendicular to a line joining the closest points of the two electrodes, then there is at least one Type A slice which comprises a part of the PTC element and at least one Type B slice whose thermal and electrical characteristics are such that, when the current through the device is increased rapidly from a level at which the PTC element is in a low temperature, low resistance state to a level which converts the PTC element into a high temperature, high resistance state, the Type B slice increases in temperature at a rate which is greater than the rate at which the PTC element in the Type A slice increases an temperature; subject to the proviso that neither of the slices adjacent an electrode is a Type B slice which comprises a part of the PTC element in contiguity with the electrode.

Claim 3

A device according to claim 1 wherein each of said electrode has an electrically active surface of a generally columnar shape and said Type B slice has a higher face-to-face resistance at 23° C. than said Type A slice.

Claim 4

A device according to claim 2 wherein the face-to-face resistance of said Type B slice is at least 1.2 times the face-to-face resistance of said Type A slice.

Claim 5

A device according to claim 2 wherein the conductive polymer in the Type A slice has substantially the same resistivity as the conductive polymer in the Type B slice.

Claim 6

A device according to claim 4 wherein the conductive polymers in the Type A and Type B slices are the same.

Claim 7

A device according to claim 5 wherein the volume enclosed by the periphery of the conductive polymer element in the Type B slice is less than the volume enclosed by the periphery of the conductive polymer element in the Type A slice.

Claim 8

A device according to claim 6 wherein the area occupied by conductive polymer in at least one of the faces of the Type B slice is less than the effective surface area of at least one of the electrodes.

Claim 9

A device according to claim 5 wherein the Type B slice comprises, within the periphery of the conductive polymer element, at least one first portion composed of a conductive polymer and at least one second portion comprising a material having a resistivity at 23° C. higher than said conductive polymer.

Claim 10

A device according to claim 8 wherein said second portion is substantially non-conducting when current is passed through the device at 23° C.

Claim 11

A device according to claim 9 wherein the second portion is composed of an insulating material.

Claim 12

A device according to claim 2 wherein said conductive polymer element consists essentially of said PTC element.

Claim 13

A device according to claim 2 wherein said conductive polymer element including an element composed of conductive polymer exhibiting ZTC behavior.

Claim 14

A device according to claim 12 wherein the resistivity at 23° C. of said conductive polymer exhibiting ZTC behavior is higher than the resistivity at 23° C. of said conductive polymer exhibiting PTC behavior.

Claim 15

A device according to claim 1 wherein the periphery of the conductive polymer element in the Type B slice is more efficiently thermally insulated than the periphery of the conductive polymer element in the Type A slice.

Claim 16

A device according to claim 1 wherein each of said electrodes has an electrically active surface of a generally columnar shape and the principal current flow, when the electrodes are first connected to a source of electrical power with the device at 23° C. lies in the plane which includes the closest points of the two electrodes.

Claim 17

A device according to claim 1 wherein the Type B slice comprises heating means which is independent of the conductive polymer element.

Claim 18

An electrical circuit which comprises (a) a source of electrical power; (b) an electrical load; and (c) a circuit protection device whose resistance at 23° C. is less than 100 ohms and less than 5% of the total resistance of the circuit at 23° C., whose largest dimension in less than 12 inches and which comprises (1) a conductive polymer element, at least a part of which is a PTC element, and (2) two electrodes, at least one of which has an electrically active surface of a generally columnar shape, and which can be connected to a source of electrical power and, when so connected, cause current to flow through said PTC element; said device being such that, if the portion thereof between the electrodes is divided into parallel-faced slices, the thickness of each slice being about 1/10 of the distance between the closest points of the two electrodes and the faces of the slices being planes which are perpendicular to a line joining the closest points of the two electrodes, then there is at least one Type A slice which comprises a part of the PTC element and at least one Type B slice whose thermal and electrical characteristics are such that, when the current through the device is increased rapidly from a level at which the PTC element is in a low temperature, low resistance state to a level which converts the PTC element into a high temperature, high resistance state, the Type B slice increases in temperature at a rate which is greater than the rate at which the PTC element in the Type A slice increases in temperature; subject to the proviso that neither of the slices adjacent an electrode is a Type B slice which comprises a part of the PTC element in contiguity with the electrode.

Claim 19

An electrical circuit which comprises (a) a source of electrical power; (b) an electrical load; and (c) a circuit protection device whose resistance at 23° C. is less than 100 ohms and less than 5% of the total resistance of the circuit at 23° C., whose largest dimension in less than 12 inches and which comprises (1) a conductive polymer element, at least a part of which is a PTC element, and (2) two electrodes, at least one of which has an electrically active surface of a generally columnar shape, and which can be connected to a source of electrical power and, when so connected, cause current to flow through said PTC element; said device being such that, if the portion thereof between the electrodes is divided into parallel-faced slices, the thickness of each slice being about 1/10 of the distance between the closest points of the two electrodes and the faces of the slices being planes which are perpendicular to a line joining the closest points of the two electrodes, then there is at least one Type A slice which comprises a part of the PTC element and at least one Type B slice whose thermal and electrical characteristics are such that, when the current through the device is increased rapidly from a level at which the PTC element is in a low temperature, low resistance state to a level which converts the PTC element into a high temperature, high resistance state, the Type B slice increases in temperature at a rate which is greater than the rate at which the PTC element in the Type A slice increases in temperature; subject to the proviso that neither of the slices adjacent an electrode is a Type B slice which comprises a part of the PTC element in contiguity with the electrode.

Claim 20

A circuit according to claim 17 wherein each of said electrodes has an electrically active surface of a generally columnar shape and said Type B slice has a higher face-to-face resistance at 23° C. than said Type A slice.

Claim 21

A circuit according to claim 18 wherein the face-to-face resistance of said Type B slice is at least 1.2 times the face-to-face resistance of said Type A slice.

Claim 22

A circuit according to claim 18 wherein the conductive polymer in the Type A slice has substantially the same resistivity as the conductive polymer in the Type B slice.

Claim 23

A circuit according to claim 20 wherein the conductive polymers in the Type A and Type B slices are the same.

Claim 24

A circuit according to claim 21 wherein the volume enclosed by the periphery of the conductive polymer element in the Type B slice is less than the volume enclosed by the periphery of the conductive polymer element in the Type A slice.

Claim 25

A circuit according to claim 22 wherein the area occupied by conductive polymer in at least one of the faces of the Type B slice is not more than the effective surface area of at least one of the electrodes.

Claim 26

A circuit according to claim 21 wherein the Type B slice comprises, within the periphery of the conductive polymer element, at least one first portion composed of a conductive polymer and at least one second portion comprising a material having a resistivity at 23° C. higher than said conductive polymer.

Claim 27

A circuit according to claim 24 wherein said second portion is substantially non-conducting when current is passed through the device at 23° C.

Claim 28

A circuit according to claim 25 wherein the second portion is composed of an insulating material.

Claim 29

A circuit according to claim 18 wherein said conductive polymer element consists essentially of said PTC element.

Claim 30

A circuit according to claim 18 wherein said conductive polymer element includes an element composed of conductive polymer exhibiting ZTC behavior.

Claim 31

A circuit according to claim 28 wherein the resistivity at 23° C. of said conductive polymer exhibiting ZTC behavior is higher than the resistivity at 23° C. of said conductive polymer exhibiting PTC behavior.

Claim 32

A circuit according to claim 17 wherein the periphery of the conductive polymer element in the Type B slice is more efficiently thermally insulated than the periphery of the conductive polymer element in the Type A slice.

Claim 33

A circuit according to claim 17 wherein each of said electrodes has an electrically active surface of a generally columnar shape and the principal current flow, when the electrodes are first connected to a source of electrical power with the device at 23° C., lies in the plane which includes the closest points of the two electrodes.

Claim 34

A circuit according to claim 17 wheren the Type B slice comprises heating means which is independent of the I 2 R heating of the conductive polymer element by passage of current therethrough between the electrodes.