Patent Application
20190131101
Embodiments of the present disclosure relate generally to the field of circuit protection devices, and more particularly to polymeric positive temperature coefficient (PPTC) devices.
Polymeric positive temperature coefficient (PPTC) devices are used to provide resettable overcurrent protection in many applications, e.g., consumer electronics and automotive applications. During an overcurrent condition, a PPTC device may rapidly increase in temperature, which in turn causes the resistance of the PPTC device to increase to effectively establish an open circuit and mitigate potentially damaging follow on currents. Subsequently, when the temperature of the PPTC cools to an acceptable level, the PPTC device may “reset” (i.e., the resistance of the PPTC device may drop to a pre-overcurrent level) and may conduct current as in normal operation.
Some PPTC devices may be adapted to support high “hold currents.” A “hold current” is a maximum current that a PPTC device may conduct before the temperature and resistance of the PPTC device increase to impede current flow. However, devices that support high hold currents are typically large and are not suitable for applications that require small form factors, and efforts to reduce device size may be costly.
It is with respect to these and other considerations that the present improvements may be useful.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter.
An exemplary embodiment of an overcurrent protection device in accordance with the present disclosure may include a first electrode disposed substantially parallel to a second electrode, a material disposed between the first electrode and the second electrode, and a plurality of conductive material nodules disposed in the material between the first electrode and the second electrode, including a first conductive material nodule at least partially contacting an inner surface of the first electrode and a second conductive material nodule at least partially contacting an inner surface of the second electrode and the first conductive material nodule. In response to an overcurrent condition the material may be configured to expand, such that the contact between the first electrode, the first conductive material nodule, the second conductive material nodule, and the second electrode is at least partially interrupted.
According to another exemplary embodiment of the present disclosure, an overcurrent protection device may include a first electrode disposed substantially parallel to a second electrode, a mesh disposed between the first electrode and the second electrode, the mesh contacting an inner surface of the first electrode and an inner surface of the second electrode, and a material disposed on the mesh and between the first electrode and the second electrode. In response to an overcurrent condition the material may be configured to expand, such that the contact between the mesh, the first electrode, and the second electrode is at least partially interrupted.
According to another exemplary embodiment of present disclosure, a method of forming an overcurrent protection device may include forming a mesh between a first electrode and a second electrode, the mesh contacting an inner surface of the first electrode and an inner surface of the second electrode, and applying a material on the mesh between the first electrode and the second electrode. In response to an overcurrent condition, material may be expanded such that the contact between the mesh, the first electrode, and the second electrode is at least partially interrupted.
By way of example, specific embodiments of the disclosed device will now be described, with reference to the accompanying drawings, in which:
An overcurrent protection device, or PPTC device, in accordance with the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain exemplary embodiments of the overcurrent protection device are presented. The overcurrent protection device may be embodied in many different forms and is not to be construed as being limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete, and will convey certain exemplary aspects of the overcurrent protection device to those skilled in the art. In the drawings, like numbers refer to like elements throughout unless otherwise noted.
In a normal condition, as illustrated in
In the event of an overcurrent condition, as shown in
In some embodiments, the device 100 may be resettable, in that when the temperature of the device 100 decreases to an acceptable level, the polymer material 125 contracts to its normal state, thereby allowing conductivity through the device 100. When the polymer material 125 is in its contracted state the mesh 120 and the electrodes 105a, 105b may once again contact each other to allow for current flow through the device 100. In some embodiments, although the temperature may decrease to an acceptable level for the device 100 to reset, the fault condition may not be removed. For example, the device 100 may not latch in a tripped state, similar to a bimetal device.
In certain embodiments, the first and second electrodes 105a, 105b made be formed of a conductive metal material, e.g., copper, nickel, or an alloy thereof. In some embodiments, the electrodes 105a, 105b may be a foil. The mesh 120 may also be formed of a conductive material, e.g., copper, steel, stainless steel, brass, aluminum, niobium, or an alloy thereof. The polymer material 125 may be an organic thermoplastic material, having a melting point between approximately 60° C. and approximately 220° C., and may be cross-linked by radiation or a chemical process. The polymer material 125 may be any thermoplastic material which expands when heat is applied to surrounding components, including but not limited to polyvinylidene fluoride (PVDF), polyvinylidene difluoride, polyethylene, ethylene tetrafluoroethylene, ethylene vinyl acetate, ethylene butyl acrylate and other materials having similar characteristics.
Referring now to
As described above, the mesh 120 may be formed by interconnected strands that define a plurality of interstices.
Referring now to
For devices 500, 500′, the material 525 may be a thermoplastic material, e.g., including but not limited to polyvinylidene fluoride (PVDF), polyvinylidene difluoride, polyethylene, ethylene tetrafluoroethylene, ethylene vinyl acetate, ethylene butyl acrylate, and other materials having similar characteristics. The plurality of conductive material nodules 530a, 530b may be formed of a conductive metal material, and may have a concentration of up to approximately 10%, or up to approximately 50%. In some embodiments, the plurality of conductive material nodules 530a, 530b may be formed of a copper, nickel, or alloy thereof.
It may be advantageous to impregnate the material 525 with the plurality of conductive material nodules 530a, 530b, so that the device 500 maintains an open state in the event of an overcurrent condition. As described above, a device may continually open and close as the polymer expands and contracts depending on the heat generated by the resistance, e.g., the device may not latch in its tripped state. As described above, this may allow devices to continually trip and reset based only on the temperature of the device like in a bimetal device. By including the plurality of conductive material nodules 530a, 530b, in the material 525, the heat generated in an overcurrent condition may maintain the open state by the expanded material 525 until the fault is removed from the device 500 and is sufficiently cooled to reset. For example, when the device 500, 500′ trips and is in a state of high resistance, the plurality of conductive material nodules 530a, 530b, may still conduct a low level of electrical current. Although some current may be able to flow via the plurality of conductive material nodules 530a, 530b, the flow of current may be substantially reduced to prevent damage to sensitive electrical components connected to the device 500, 500′. In some embodiments, temperatures may range from approximately 60° C. to 350° C., and the hold current may reach up to approximately 10 amps. With a low level of current being able to flow through the conductive material nodules 530a, 530b, the device 500, 500′ may remain heated to maintain an open condition until the fault is removed. So that the device 500, 500′ remains latched until the fault is removed may be advantageous for protecting sensitive electrical devices connected to the device 500, 500′.
When the device 500, 500′ operates normally, current may flow from the first electrode 505a, through the mesh 520 (if present) and a plurality of conductive material nodules 530a, 530b, and to the second electrode 505b, or vice versa, between terminals (not shown). In some embodiments, the mesh 520 contacting the first and second electrodes 505a, 505b may allow for current to flow through the device 500. In an overcurrent event, the resistance of the device 500, 500′ may rapidly increase, generating heat in the device 500. As the device 500 increases in temperature, the material 525 may expand, thereby at least partially interrupting the connection between the first electrode 505a, mesh 520 (if present), and second electrode 505b. As described above, the conductive material nodules 530a, 530b may allow a low level of current. The presence of the conductive material nodules 530a, 530b in the material 525 may result in the material 525 remaining heated for a period of time after the overcurrent condition occurs. With the conductive material nodules 530a, 530b remaining heated, an expanded configuration of the material 525 may maintain the device 500 in an open configuration until the fault is removed and the device 500, 500′ is sufficiently cooled to “reset” (i.e., reestablish electrical conduction).
As shown in
The configuration illustrated in
As used herein, references to “an embodiment,” “an implementation,” “an example,” and/or equivalents is not intended to be interpreted as excluding the existence of additional embodiments also incorporating the recited features.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize its usefulness is not limited thereto and the present disclosure can be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below are to be construed in view of the full breadth and spirit of the present disclosure as described herein.
