THERMAL PROTECTION DEVICE TO WITHSTAND HIGH VOLTAGE

A thermal protection device, comprising: 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.

BACKGROUND

Field

Embodiments relate to the field of resistance heaters, and more particularly to heaters based upon PPTC materials.

Discussion of Related Art

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.

BRIEF SUMMARY

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.

DESCRIPTION OF EMBODIMENTS

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.

FIG.1illustrates a thermal protection circuit100, according to embodiments of the disclosure.FIG.1Aillustrates operation of the thermal protection circuit100ofFIG.1A, during normal conditions.FIG.1BandFIG.1Ccollectively illustrate operation of the thermal protection circuit100ofFIG.1A, during an abnormal event. As shown inFIG.1, the thermal protection circuit100includes a first PTC device102, arranged in a PTC circuit108, and having a first input side112, coupled to an input path103of the PTC circuit108, and having a first output side114, coupled to an output path105of the PTC circuit108. The thermal protection circuit100further includes a second PTC device104, having a second input side116, coupled to the input path103of the PTC circuit108, and having a second output side118, coupled to the output path105of the PTC circuit108. The thermal protection circuit also includes a thermal fuse or similar thermal element, referred to herein as a thermal link106, having a third input side120, coupled to the first output side114of the first PTC device102and the second output side118of the second PTC device104, via the output path105of the PTC circuit108.

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 device102and the second PTC device104may 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.

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 device102is arranged with a first trip temperature, and the second PTC device104is arranged with a second trip temperature, greater than the first trip temperature. In addition, a first electrical resistivity of the first PTC device102may be arranged to be less than a second electrical resistivity of the second PTC device104. In some non-limiting examples, the electrical resistivity of the first PTC device102may 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 device104.

In operation, the thermal protection circuit100may be coupled to protect any suitable component, shown as component150, representing a device, circuit, or other entity to be protected. Examples of protection may include limiting current to the component150to an acceptable limit for a given operating voltage.

Turning now toFIG.1A, there is shown the operation of the thermal protection circuit100ofFIG.1A, during normal conditions. Under this scenario, electrical current may pass through thermal protection circuit100to component150. The electrical current may be within an acceptable range and may accordingly pass through the thermal protection circuit100along a predetermined path. For example, when the resistance of the first PTC device102is, for example, 10× or 100× lower than the resistance of the second PTC device104, most, if not all, of the incident current122passing through PTC circuit108may be conducted through first PTC device102and through thermal link106, which component may be highly electrically conductive. As such, the thermal link106may not be affected by the level of the incident current122passing through the thermal protection circuit100.

FIG.1Billustrates operation of the thermal protection circuit100ofFIG.1A, during an abnormal event. The abnormal event may be such that the first PTC device102is tripped. In other words, the abnormal event may cause the temperature of the first PTC device102to exceed the trip temperature of the first PTC device102. One example of an abnormal event is an excess current that causes a PTC device to trip. When a current flows through a PTC device, the heat generated raises the temperature of the PTC device. In the event of excess current, the internal temperature of the first PTC device102may reach the trip temperature, where the resistivity of the first PTC device102increases by two orders of magnitude, three orders or magnitude, four orders of magnitude, and so forth. As such, current flow may be blocked by the first PTC device102, where the incident current130during the abnormal event is directed as bypass current130B to the second PTC device104, which device may initially conduct the excess current therethrough, shown as current130C.

At the same time the bypass current130B will cause a temperature increase in the second PTC device104, and may cause the second PTC device104to exceed the trip temperature of the second PTC device104. The abrupt increase in resistivity of second PTC device104in a tripped state will also increase the heat134generated by the second PTC device104in response to the bypass current130B passing therethrough.

Turning now toFIG.1Cthere is shown a later instance after the instance ofFIG.1B, during the abnormal event, where the heat134, generated from second PTC device104, melts the thermal link106, causing an open circuit condition where current no longer flows through thermal protection circuit100. By providing the second PTC device104in parallel to the first PTC device102, the branch of the PTC circuit108that includes the second PTC device104effectively forms a heater circuit, where the second PTC device104is triggered to heat the thermal link106when first the PTC device102is triggered, diverting current to the second PTC device104.

Note that in various embodiments, the second PTC device104may be in thermal proximity to the thermal link106. In this manner, the thermal link106may 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.FIG.2shows exemplary resistance data as a function of temperature for a first PPTC device (PTC1) and a second PPTC device (PTC2), according to embodiments of the disclosure. In this case, the first PPTC device has a trigger temperature in the range of 160 degrees and the second PPTC device has a trigger temperature in the range of 230 C. Note that in this manner, the first PTC device may serve as a sensor to trigger under overheating, while the second PTC device is used to melt a thermal link, so that the triggering temperature of the first PTC device is to be set lower than the thermal link melting temperature. In this regard, suitable materials for the thermal link according to some non-limiting embodiments include a lead free solder or, alternatively, a lead-containing solder. More generally, the relationship between the various temperatures of the components is trigger (trip) temperature of PTC1<melting temperature of Thermal-link<trip (trip-state) temperature of PTC2. Note that because in embodiments of the disclosure, the PTC2is triggered by the current, the actual trigger (trip) temperature of the PTC2is not so important. When the PTC2is triggered by excess current to enter the trips state, the heat generated during trip state melts the thermal link, so the PTC2trip temperature (at low current) should be higher than melting point of the thermal link.

Thus, the setting of a relatively wider gap between trip temperatures of PTC1and PTC2will afford the ability to use different thermal links, having a wider range of fuse temperatures that fall between the trigger temperatures of PTC1and PTC2.

FIG.3is a composite graph showing exemplary temperature and current behavior of a PTC based thermal protection circuit, arranged according to embodiments of the disclosure. In this example, a circuit similar to the circuit ofFIG.1is tested at 850 V DC and 4 A current. The whole circuit is heated from room temperature at a rate of 2 C/min, while current and temperature are monitored. The lowest of the three temperature curves represents the ambient temperature as a function of time, while the other two curves represent the temperature of the first PTC device (PTC1) and the second PTC device (PTC2). At approximately 2750 seconds heating time, the ambient temperature reaches 105 C. At this point, the first PTC device reaches a trigger point, meaning the combination of the 4 A current and the ambient temperature causes the first PTC device to reach a trigger point, causing a sharp increase in temperature. At nearly the same time, the second PTC device is also triggered, by virtue of the shunting of the 4 A current through the second PTC device, generally as explained above with respect toFIGS.1B-1C. This causes a sharp increase in temperature to 123 C as shown. This increase in temperature results in opening of a thermal link, which opening results in the current dropping to zero, as shown.

FIG.4illustrates a thermal protection circuit200, according to further embodiments of the disclosure. In this example, a thermal link106is provided, generally as described above with respect toFIG.1. For example, the thermal link106may form part of a main protection circuit202that limits current to the component150. As shown, the thermal link106is arranged in electrical series with the component150along the electrical path204. The thermal protection circuit200also includes a PPTC heater206, arranged in thermal proximity to the thermal link106. The PPTC heater206may be the same as or similar to the second PTC device104, described above. The PPTC heater206is arranged in a heater circuit208along an electrical path210, separate from the electrical path204. During an abnormal event, when the combination of ambient temperature and current passing through the PPTC material of PPTC heater206causes the PPTC heater206to exceed the trip temperature of the PPTC heater206, the PPTC heater206may transition to a high resistivity state, and at the same time generate heat134, as described above. In this manner, the heat134may cause to thermal link106to open, thus protecting the component150from excessive current.

An advantage of the embodiment ofFIG.4is that because the is triggered by an external (input signal to210), the timing of when the thermal link106is triggered to fuse and create an open circuit is controllable.

FIG.5Aillustrates a thermal protection circuit in top view, according to embodiments of the disclosure, whileFIG.5Billustrates the thermal protection circuit ofFIG.5Ain cross-section, according to embodiments of the disclosure. The thermal protection circuit500may be considered a variant of the thermal protection circuit ofFIG.4. A pair of conductors, shown as external conductors502are disposed on opposite sides of a thermal link504, where the thermal link504may be an electrically conductive fusable material, as discussed previously. As such, the external conductors502and thermal link504define a conductive path520, shown inFIG.5B. The conductive path520may form part of a circuit of a device or other circuitry to be protected. In the thermal protection circuit500, an electrically insulating substrate510is provided subjacent to a pair of electrically conductive pads, shown as conductive pads508. The conductive pads508are in electrical contact with the external conductors502, and are separated from one another by a gap507.

The thermal protection circuit500further includes a PPTC heater506that is formed of a PPTC body512, disposed between two electrodes, shown as an upper conductive layer516, and lower conductive layer514. As in PPTC heater206, external conductors, such as a lead (not shown), may be coupled to the each of the electrodes of the PPTC heater506to drive electrical current through the PPTC heater in an electrical circuit, separate from the electrical circuit formed by conductive path520.

Note that while the electrically insulating substrate510is a poor electrical conductor, for optimal operation, the electrically insulating substrate510is a good thermal conductor, so that heat generated by the PPTC heater506is efficiently and rapidly transferred to the thermal link504. Suitable materials for electrically insulating substrate510include 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 substrate510by using a metal layer as thermal conductor.

As illustrated inFIG.5B, a solder layer518is provided between the PPTC heater506and the electrically insulating substrate510. A solder layer518may also be provided on the top of conductive pads508to connect conductive pads508to external conductors502. In addition, a lower metal layer522may be provided on the electrically insulating substrate510to bond the electrically insulating substrate510to solder layer518, and thus to PPTC heater506.

Under normal operation, electrical current may traverse the thermal protection circuit500, through external conductors502, thermal link504and conductive pads508, and may be conducted through any external circuitry to be protected. However, under a fault condition, the PPTC heater506may be triggered by a controller532that directs a triggering current to be sent from a current source530, so that the triggering current passes through the PPTC body512. In turn, the triggering current causes the PPTC body to generate heat that is sufficient to fuse the thermal link504, creating an electrical open between the first one of conductive pads508and second one of conductive pads508, in the region of the gap507.

FIG.6illustrates another thermal protection circuit, according to further embodiments of the disclosure. The thermal protection circuit600is arranged with similar features as the embodiment ofFIG.1, with like elements labeled the same. In the thermal protection circuit600, an additional terminal is coupled to the second PTC device104, shown as trigger terminal602. In this embodiment, in addition to the features of thermal protection circuit100, discussed above, the trigger terminal602may be coupled for remote and external triggering, to trigger the second PTC device to act as a PTC heater in order to heat the thermal link106. In operation, the PTC2is triggered by the current input from the trigger terminal602. In this embodiment, triggering of the PTC heater may be more rapid that in the embodiment ofFIG.4.

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.