A flexible sheet of positive temperature coefficient (PTC) material formed of a polymer resin and a conductive filler, the sheet of PTC material having a thickness in a range of 10 m to 100 m. A method for forming the flexible sheet of positive temperature coefficient material may include preparing a PTC ink from a polymer resin, a conductive filler, and a solvent, applying the PTC ink to a substrate, pulling a blade over the PTC ink to create a uniformly thick layer of the PTC ink on the substrate, and allowing the PTC ink to dry so that the solvent evaporates and leaves a solid layer of PTC material on the substrate.

Provided is an overcurrent protection element comprising: a core material comprising a top surface, a bottom surface opposite the top surface, a first side surface and a second side surface both located between the top and bottom surfaces, and a first end surface and a second end surface both located between the top and bottom surfaces. A first conductive layer is formed on the top surface of the core material, and a second conductive layer is formed on the bottom surface of the core material. An encapsulation layer covers the first conductive layer, the second conductive layer, and at least one of the side surfaces. A first terminal electrode is electrically connected to the first conductive layer, and a second terminal electrode is electrically connected to the second conductive layer. The overcurrent protection element has excellent electric conductivity, fast response, and sufficient self-protection during soldering process and in use.

A PTC circuit protection device includes a PTC polymer material and two electrodes attached to the PTC polymer material. The PTC polymer material includes a polymer matrix and a particulate conductive filler dispersed in the polymer matrix. The polymer matrix is made from a polymer composition that contains a non-grafted polyolefin. The conductive filler includes tungsten carbide particles having a total carbon content that is less than 6.0 wt % based on the total weight of the tungsten carbide particles.

A surface-mountable over-current protection device comprises at least one chip, a first lead and a second lead. The chip comprises a PTC material layer and two metal electrode layers disposed on upper and lower surfaces of the PTC material layer. The first lead is bent into multiple portions comprising a first electrode connecting portion connecting to one of the two metal electrode layers of the at least one chip and a first soldering portion for surface-mounting. The second lead is bent into multiple portions comprising a second electrode connecting portion connecting to another one of the two electrode layers of the at least one chip and a second soldering portion for surface-mounting. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein, and the conductive filler has a resistivity less than 500.Math.cm. The surface-mountable over-current protection device can withstand a cycle life test of 300 cycles at 20V/40A without blowout.

A surface-mountable over-current protection device comprises at least one chip, a first lead and a second lead. The chip comprises a PTC material layer and two metal electrode layers disposed on upper and lower surfaces of the PTC material layer. The first lead is bent into multiple portions comprising a first electrode connecting portion connecting to one of the two metal electrode layers of the at least one chip and a first soldering portion for surface-mounting. The second lead is bent into multiple portions comprising a second electrode connecting portion connecting to another one of the two electrode layers of the at least one chip and a second soldering portion for surface-mounting. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein, and the conductive filler has a resistivity less than 500 .Math.cm. The surface-mountable over-current protection device can withstand a cycle life test of 300 cycles at 20V/40 A without blowout.

The present invention provides a conductive polymer composition, a conductive polymer sheet, an electrical device, and their preparation methods. The conductive polymer composition of the present invention includes a polymer and a conductive powder at a volume ratio of 35:65 to 65:35. The polymer includes at least one semicrystalline polymer selected from polyolefin, a copolymer of at least one olefin and at least one non-olefinic monomer copolymerizable therewith, and a thermoformable fluorine-containing polymer. The stated conductive powder includes at least one powder of a transition metal carbide, a transition metal carbon silicide, a transition metal carbon aluminide, and a transition metal carbon stannide. And the stated size distribution of the conductive powder satisfies: 20>D.sub.100/D.sub.50>6, where D.sub.50 denotes a corresponding particle size when a cumulative particle-size distribution percent in the conductive powder reaches 50%, and D.sub.100 denotes a maximum particle size. The stated conductive polymer composition has excellent processability, and can be used for preparing a PPTC device with ultralow resistance and stability in air without an oxygen barrier coating.

An over-current protection device comprises first and second electrode layers and a PTC material layer laminated therebetween. The PTC material layer has a resistivity less than 0.05 .Math.cm and comprises a polymer matrix, a conductive ceramic filler and a carbon-containing conductive filler. The polymer matrix comprises a fluoropolymer having a melting point higher than 150 C. and comprises 50-60% by volume of the PTC material layer. The conductive ceramic filler having a resistivity less than 500.Math.cm is dispersed in the polymer matrix and comprises 40-45% by volume of the PTC material layer. The carbon-containing conductive filler is dispersed in the polymer matrix and comprises 0.5-5% by volume of the PTC material layer. At 25 C., a ratio of a hold current to an area of the over-current protection device is 0.21-0.3 A/mm.sup.2, and a ratio of an endurable power to the area of the over-current protection device is 4.8-7.2 W/mm.sup.2.

A PTC circuit protection device, includes: two PTC units, each of the PTC units including a first insulating layer, a first electrically conductive layer, a PTC polymeric layer, a second electrically conductive layer, a second insulating layer, a first electrode, a second electrode; an insulating bridge layer interconnecting the first insulating layers of the PTC units; and first and second gaps formed between the PTC units and located at two opposite sides of the insulating bridge layer.

A pre-charge circuit. The precharge circuit may include a switching device for controlling a voltage to be supplied to a battery; and a heterogeneous thermistor circuit, coupled to the switching device. The heterogeneous thermistor circuit may include a negative temperature coefficient (NTC) component; and a polymer positive temperature coefficient (PPTC) component, arranged in electrical series with the NTC component and the switching device.

A hybrid circuit protection device includes a positive temperature coefficient (PTC) component, a voltage-dependent resistor, a gas discharge tube (GDT), and first and second conductive leads that are respectively connected to the PTC component and the GDT. The voltage-dependent resistor and the PTC component are electrically connected in series, the GDT is electrically connected to the voltage-dependent resistor and the PTC component, and the GDT has a breakdown voltage greater than a varistor voltage of the voltage-dependent resistor as determined at 1 mA.