Embodiments relate to the field of resistance heaters, and more particularly to heaters based upon PPTC materials.
Automobiles and other apparatus may include components that are designed to operate over a wide temperature range. Examples of components that may operate over a wide temperature range include electronic circuits used to control various components in an automobile, as well as batteries used to power automobiles.
In order to protect various electrical and electronic components and circuits, various known devices may be deployed, including thermal protection devices, overvoltage protection devices, as well as overcurrent protection devices.
With respect to this and other considerations the present disclosure is provided.
In one embodiment, a thermal protection circuit may include a first PTC device, arranged in a PTC circuit, and having a first input side, coupled to an input path of the PTC circuit, and having a first output side, coupled to an output path of the PTC circuit; a second PTC device, arranged in the PTC circuit, and having a second input side, coupled to the input path of the PTC circuit, and having a second output side, coupled to the output path of the PTC circuit; and a thermal link having a third input side, coupled to the first output side of the first PTC device and the second output side of the second PTC device, via the output path of the PTC circuit.
In another embodiment, a method of providing thermal protection may include conducting current through a protection circuit, the protection circuit comprising a first PTC device and a second PTC device, arranged in electrically parallel fashion to one another within a PTC circuit, and further comprising a thermal link, arranged in electrical series to the PTC circuit; and responsive to an abnormal condition, changing the first PTC device from a normal state to a tripped state, wherein the second PTC device transitions from a normal conduction state to a tripped state after the tripping the first PTC device, and wherein the second PTC device causes the thermal link to melt.
In a further embodiment, a thermal protection circuit may include a thermal link, arranged along a first current path, the first current path being coupled to an external component; and a PPTC heater, disposed in thermal proximity to the thermal link, the PPTC heater comprising a PPTC device arranged along a second current path, separate from the first current path.
The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The embodiments are not to be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey their scope to those skilled in the art. In the drawings, like numbers refer to like elements throughout.
In the following description and/or claims, the terms “on,” “overlying,” “disposed on” and “over” may be used in the following description and claims. “On,” “overlying,” “disposed on” and “over” may be used to indicate that two or more elements are in direct physical contact with one another. Also, the term “on,”, “overlying,” “disposed on,” and “over”, may mean that two or more elements are not in direct contact with one another. For example, “over” may mean that one element is above another element while not contacting one another and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect.
In various embodiments, a novel thermal protection circuit is provided based upon a combination of a PTC circuit and thermal link, or thermal fuse. The thermal protection circuit may be used to protect any suitable object, component, circuit, or combination of the above, according to various non-limiting embodiments. As detailed below, in various embodiments, the PTC circuit may include a first PTC device having a first input side, coupled to an input path of the PTC circuit, and having a first output side, coupled to an output path of the PTC circuit. The PTC circuit may further include a second PTC device, having a second input side, coupled to the input path of the PTC circuit, and having a second output side, coupled to the output path of the PTC circuit. The thermal link of the thermal protection circuit may have a third input side, coupled to the first output side of the first PTC device and the second output side of the second PTC device, via the output path of the PTC circuit. As explained below, this circuit architecture provides advantageous protection in the case of an abnormal event.
In accordance with various embodiments of the disclosure, the term PTC device may refer to a device formed of a positive temperature coefficient (PTC) material, where the PTC device is a resettable device that acts to limit current by exhibiting a large increase in resistivity at a given temperature, often referred to as a trip temperature. In specific embodiments, one or more of the first PTC device 102 and the second PTC device 104 may be formed of polymer PTC materials (PPTC) materials. A suitable PTC material or PPTC material may include a polymer matrix, formed of one or more suitable polymers, as well as a conductive filler, such as carbon, metallic powder, graphene, or other known filler materials. Materials properties, such as normal state resistivity may be tailored by adjusting the relative percent of conductive filler with respect to the overall PTC material, including polymer matrix.
Regarding the polymer matrix for a PTC device, suitable materials for PTC device 102 according to non-limiting embodiments include semi-crystalline polymers, e.g., polyethylene, polyvinylidene fluoride, ethylene tetrafluoroethylene, ethylene-vinyl acetate, ethylene and acrylic acid copolymer, ethylene butyl acrylate copolymer, polycaprolactone, polyurethane, and polyester. According to some non-limiting embodiments, suitable materials for second PTC device 104 include semi-crystalline polymers, e.g., polyethylene, polyvinylidene fluoride, perfluoroalkoxy alkane, ethylene tetrafluoroethylene, ethylene-vinyl acetate, ethylene and acrylic acid copolymer , ethylene butyl acrylate copolymer.
As known in the art, the trip temperature of a PTC device may be set by the melting temperature or softening temperature of the polymer matrix of the PTC material. In various embodiments, the first PTC device 102 is arranged with a first trip temperature, and the second PTC device 104 is arranged with a second trip temperature, greater than the first trip temperature. In addition, a first electrical resistivity of the first PTC device 102 may be arranged to be less than a second electrical resistivity of the second PTC device 104. In some non-limiting examples, the electrical resistivity of the first PTC device 102 may be a factor of 10× lower, a factor of 50× lower, or a factor of 100× lower than the electrical resistivity of the second PTC device 104.
In operation, the thermal protection circuit 100 may be coupled to protect any suitable component, shown as component 150, representing a device, circuit, or other entity to be protected. Examples of protection may include limiting current to the component 150 to an acceptable limit for a given operating voltage.
Turning now to
At the same time the bypass current 130B will cause a temperature increase in the second PTC device 104, and may cause the second PTC device 104 to exceed the trip temperature of the second PTC device 104. The abrupt increase in resistivity of second PTC device 104 in a tripped state will also increase the heat 134 generated by the second PTC device 104 in response to the bypass current 130B passing therethrough.
Turning now to
Note that in various embodiments, the second PTC device 104 may be in thermal proximity to the thermal link 106. In this manner, the thermal link 106 may be caused to open in rapid fashion in response to an abnormal event.
As noted previously, the trigger temperature of the first PTC device may be lower than the trigger temperature of the second PTC device.
Thus, the setting of a relatively wider gap between trip temperatures of PTC1 and PTC2 will afford the ability to use different thermal links, having a wider range of fuse temperatures that fall between the trigger temperatures of PTC1 and PTC2.
An advantage of the embodiment of
The thermal protection circuit 500 further includes a PPTC heater 506 that is formed of a PPTC body 512, disposed between two electrodes, shown as an upper conductive layer 516, and lower conductive layer 514. As in PPTC heater 206, external conductors, such as a lead (not shown), may be coupled to the each of the electrodes of the PPTC heater 506 to drive electrical current through the PPTC heater in an electrical circuit, separate from the electrical circuit formed by conductive path 520.
Note that while the electrically insulating substrate 510 is a poor electrical conductor, for optimal operation, the electrically insulating substrate 510 is a good thermal conductor, so that heat generated by the PPTC heater 506 is efficiently and rapidly transferred to the thermal link 504. Suitable materials for electrically insulating substrate 510 include various known ceramics that exhibit electrical insulation and relatively higher thermal conductivity. In other embodiments, a resin material would be acceptable for the electrically insulating substrate 510 by using a metal layer as thermal conductor.
As illustrated in
Under normal operation, electrical current may traverse the thermal protection circuit 500, through external conductors 502, thermal link 504 and conductive pads 508, and may be conducted through any external circuitry to be protected. However, under a fault condition, the PPTC heater 506 may be triggered by a controller 532 that directs a triggering current to be sent from a current source 530, so that the triggering current passes through the PPTC body 512. In turn, the triggering current causes the PPTC body to generate heat that is sufficient to fuse the thermal link 504, creating an electrical open between the first one of conductive pads 508 and second one of conductive pads 508, in the region of the gap 507.
While the present embodiments have been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible while not departing from the sphere and scope of the present disclosure, as defined in the appended claims. Accordingly, the present embodiments are not to be limited to the described embodiments, and may have the full scope defined by the language of the following claims, and equivalents thereof.
This application claims the benefit of priority to, U.S. Provisional Patent Application No. 63/305,901, filed Feb. 2, 2022, entitled “Thermal Protection Device To Withstand High Voltage,” which application is incorporated herein by reference in its entirety.
Number | Date | Country | |
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63305901 | Feb 2022 | US |