Circuit protection devices

Abstract

An electrical device which contains a first electrode, a second electrode, a third electrode, a first resistor which is connected in series between the first and second electrodes, and a second resistor which (i) is thermally coupled to the first resistor, (ii) exhibits anomalous resistance/temperature behavior, and (iii) is connected in series between the first and third electrodes. The device has at least one of the following characteristics: (a) the first resistor and at least one of the first and second electrodes are formed from a single piece of metal; (b) the device has a generally planar configuration and comprises at least one electrical connector connected to one of the first, second, and third electrodes, whereby the first, second and third electrodes or connectors secured thereto can be secured directly to a circuit board with the device parallel to the circuit board; and (c) the second resistor is a planar sheet of a material which exhibits anomalous resistance/temperature behavior, the sheet having a first major surface to which the first and second electrodes are attached and a second major surface to which the third electrode is attached. The device can be prepared from an electrical assembly which can be divided into a plurality of devices.

What is claimed is:  
     
         1 . An electrical device which comprises: 
 (1) a first electrode;    (2) a second electrode;    (3) a third electrode;    (4) a first resistor which is connected in series between the first and second electrodes; and    (5) a second resistor which (i) is thermally coupled to the first resistor, (ii) exhibits anomalous resistance/temperature behavior, and (iii) is connected in series between the first and third electrodes;    the device having at least one of the following characteristics:    (a) the first resistor and at least one of the first and second electrodes are formed from a single piece of metal;    (b) the device has a generally planar configuration and comprises at least one electrical connector connected to one of the first, second, and third electrodes, whereby the first, second and third electrodes or connectors secured thereto can be secured directly to a circuit board with the device parallel to the circuit board; and    (c) the second resistor is a planar sheet of a material which exhibits anomalous resistance/temperature behavior, the sheet having a first major surface to which the first and second electrodes are attached and a second major surface to which the third electrode is attached.    
     
     
         2 . A device according to  claim 1  wherein the second resistor exhibits PTC behavior.  
     
     
         3 . A device according to  claim 1  wherein the second resistor is a planar sheet of a PTC material which comprises an organic polymer and, dispersed therein, a particulate conductive filler, the sheet having a first major surface and an opposite second major surface.  
     
     
         4 . A device according to  claim 3  wherein the first, second and third electrodes are first, second and third planar metal members, the first and second electrodes being secured to the first major surface of the planar PTC sheet and the third electrode being secured to the second major surface of the planar PTC sheet.  
     
     
         5 . A device according to  claim 4  which further comprises 
 6) an electrical connector which extends from the third electrode to the plane of the first and second electrodes.  
 
     
     
         6 . A device according to  claim 5  which 
 (a) further comprises 
 (7) a fourth planar metal member which is secured to the first major surface of the planar PTC sheet and is separate from the first and second electrodes; and  
 
 (b) wherein the electrical connector contacts the planar PTC sheet and is connected to the third electrode and to the fourth metal member.  
 
     
     
         7 . A device according to  claim 4  wherein the first resistor is a planar metal member which is secured to the first major surface of the planar PTC sheet.  
     
     
         8 . A device according to  claim 4  which further comprises 
 ( 8 ) a layer of electrical and thermal insulation which at least partially covers the first resistor.  
 
     
     
         9 . A device according to  claim 7  wherein the first and second electrodes and the first resistor are different parts of a single piece of metal foil.  
     
     
         10 . A device according to  claim 1  which comprises a first electrical lead which is connected to the first electrode, a second electrical lead which is connected to the second electrode, and a third electrical lead which is connected to the third electrode, the leads having distal ends.  
     
     
         11 . A device according to  claim 10  wherein the distal ends terminate in the same plane.  
     
     
         12 . A device which comprises 
 (1) a first planar metal foil electrode;    (2) a second planar metal foil electrode;    (3) a third planar metal foil electrode;    (4) a first planar metal foil resistor connected in series between the first and second electrodes; and    (5) a planar sheet of a composition which exhibits PTC behavior and which comprises a crystalline organic polymer and a particulate conductive filler dispersed in the organic polymer, the planar sheet having a first major surface and an opposite second major surface;    the first and second electrodes and the first resistor being different parts of a single piece of metal foil which is secured to the first major surface of the planar PTC sheet, and the third electrode being secured to the second major surface of the planar PTC sheet.    
     
     
         13 . A device according to  claim 12  which comprises: 
 (6) an electrical connector; and  
 (7) a fourth planar metal member which is secured to the first major surface of the planar PTC sheet and is separate from the first and second electrodes;  
 the electrical connector contacting the planar PTC sheet and connecting the third electrode and the fourth metal member.  
 
     
     
         14 . A device according to  claim 13  wherein the electrical connector passes through the planar PTC sheet.  
     
     
         15 . An electrical assembly which can be divided into a plurality of devices as claimed in  claim 12  and which comprises: 
 (1) a planar sheet of a composition which exhibits PTC behavior, the sheet having a first major surface and an opposite second major surface;  
 (2) a first planar metal foil member which is secured to the first major surface of the PTC sheet; and  
 (3) a second planar metal foil member which is secured to the second major surface of the PTC sheet;  
 at least one of the first and second metal foil members having been etched so that the assembly comprises a plurality of identical assembly sub-portions, each of the assembly sub-portions  
 (i) becoming a device as claimed in  claim 12  when the assembly is divided into a plurality of devices, and  
 (ii) comprising (a) a metal foil member which is secured to a major surface of the PTC sheet and comprises a first electrode, a second electrode and a resistor connected in series between the first and second electrodes, (b) a sub-portion of the PTC sheet, and (c), secured to the opposite face of the sub-portion of the PTC sheet, a third electrode.  
 
     
     
         16 . An assembly according to  claim 15  wherein the PTC composition comprises a crystalline organic polymer and, dispersed therein, a particulate conductive filler.  
     
     
         17 . An assembly according to  claim 16  wherein each of the assembly sub-portions comprises: 
 (4) a fourth metal foil member which (i) is secured to the same surface of the sub-portion of the PTC element the first and second electrodes, and (ii) is separate from the first and second electrodes; and  
 (5) an electrical connector which (i) passes through the sub-portion of the PTC sheet and (ii) is connected to the fourth metal foil member and to the third electrode.  
 
     
     
         18 . An assembly according to  claim 17  wherein each electrical connector, when the assembly is divided into a plurality of devices, is divided into at least two parts, each part serving as an electrical connector in a device.  
     
     
         19 . An assembly according to  claim 15  wherein the first and second metal foil members have been etched so that the assembly can be divided into the plurality of devices without dividing any of the metal foil members.  
     
     
         20 . An assembly according to  claim 19  wherein both of the first and second metal foil members have been etched so that the assembly has balanced physical properties.  
     
     
         21 . An electrical circuit which comprises 
 (1) an electrical power supply;    (2) an electrical load;    (3) a circuit interruption element connected in series with the power supply and the load;    (4) a device as defined in  claim 2;  and    (5) a control element which is 
 (a) connected in series with the first and third electrodes, and  
 (b) coupled to the circuit interruption element;  
 whereby, when there is an overcurrent through the load, the consequent reduction in current through the control element activates the circuit interruption element to reduce the current through the load.