Overcurrent protection element

Abstract

An over-current protection element comprises an electrode layer and a thermistor layer. The thermistor layer has a positive temperature coefficient characteristic and is stacked between the upper metal layer and the lower metal layer in the electrode layer. In addition, the thermistor layer contains a high-molecular polymer base material and a conductive filler. The high-molecular polymer base material comprises a first fluorine-containing polymer and a second fluorine-containing polymer. And the weight-average molecular weight of the second fluorine-containing polymer is between 630000 g / mol and 1100000 g / mol. And the conductive filler is dispersed in the high-molecular polymer base material and is used for forming a conductive channel of the thermistor layer.

Description

Technical Field

[0001] The present invention relates to an overcurrent protection element, and more particularly to a low volume resistivity overcurrent protection element used for motor stall protection. Background Art

[0002] The resistance of existing conductive composite materials with positive temperature coefficient (PTC) characteristics is very sensitive to changes in specific temperature. They can be used as materials for current sensing elements and are currently widely used in overcurrent protection elements or circuit elements. Specifically, the resistance of PTC conductive composite materials can be maintained at an extremely low value at normal temperature, allowing the circuit or battery to operate normally. However, when the circuit or battery has an overcurrent (over-current) or overtemperature (over-temperature) phenomenon, its resistance value will instantly increase to a high resistance state (at least 10 4 Ω or more), which is called a trip, and the overcurrent is cut off to protect the battery or circuit components.

[0003] As for the most basic structure of the overcurrent protection element, it is composed of a PTC material layer and metal electrodes attached to both sides thereof. The PTC material layer will at least include a substrate and a conductive filler. The substrate is composed of a high molecular polymer, and the conductive filler is dispersed in the high molecular polymer as a conductive path. For electronic devices with higher protection temperature requirements, the substrate often uses a fluorine-containing polymer (such as polyvinylidene fluoride) as its main component. In addition, the composition of the conductive filler can be roughly divided into two types: the first type of conductive filler is composed of carbon black and at least one metal compound, and the second type of conductive filler is composed of carbon black. The first type of conductive filler mentioned above can be called a low volume resistivity conductive filler, and the overcurrent protection element containing this conductive filler can be called a low volume resistivity overcurrent protection element. Traditionally, the low volume resistivity overcurrent protection element with polyvinylidene fluoride as the main component of the substrate (hereinafter referred to as "PVDF low volume resistivity overcurrent protection element") has better electrical conduction capability, but has the problem of poor thermal stability. In more detail, under the cycle of temperature rising from low temperature to high temperature and then falling from high temperature to low temperature (i.e., hot and cold shock), the resistance value of the traditional PVDF low volume resistivity overcurrent protection element gradually increases with multiple temperature rises and has a large change. The above situation is particularly obvious in the temperature section before triggering, resulting in a relatively reduced current flow, affecting the normal operation of the protected electronic device. It should be understood that the miniaturization of components is the current trend, and this thermal stability problem is further magnified as the size of the overcurrent protection component becomes smaller.

[0004] In summary, there is still considerable room for improvement in the resistance stability of existing low volume resistivity overcurrent protection components. Summary of the invention

[0005] The present invention provides an overcurrent protection element with high resistance stability and low volume resistivity. The overcurrent protection element has an electrode layer and a thermistor layer, and utilizes the positive temperature coefficient characteristics given by the thermistor layer to protect the electronic device. It should be noted that the thermistor layer of the present invention includes two fluoropolymers (i.e., the first fluoropolymer and the second fluoropolymer hereinafter), and the weight average molecular weight of the second fluoropolymer is adjusted to between 630,000 g / mol and 1,100,000 g / mol, thereby reducing the disturbance between the materials. In this way, the resistance value of the overcurrent protection element is not easily affected by temperature shock (i.e., hot and cold shock), and at the same time, it can have a lower volume resistivity for use in components with large current requirements.

[0006] According to an embodiment of the present invention, an overcurrent protection element comprises an electrode layer and a thermistor layer. The electrode layer comprises an upper metal layer and a lower metal layer. The thermistor layer contacts the upper metal layer and the lower metal layer and is stacked therebetween, wherein the thermistor layer has a positive temperature coefficient characteristic and comprises a polymer substrate and a conductive filler. The polymer substrate comprises a first fluorine-containing polymer and a second fluorine-containing polymer, wherein the weight average molecular weight of the second fluorine-containing polymer is between 630,000 g / mol and 1,100,000 g / mol. The conductive filler is dispersed in the polymer substrate to form a conductive path of the thermistor layer.

[0007] According to some embodiments, based on 100% of the volume of the thermistor layer, the first fluorine-containing polymer accounts for 12% to 42% by volume, and the second fluorine-containing polymer accounts for 1% to 31% by volume.

[0008] According to some embodiments, the second fluoropolymer is represented by formula (I):

[0009]

[0010] wherein R1 and R2 are selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4; R1 and R2 are different; and n is at least 9000.

[0011] According to some embodiments, the weight average molecular weight of the first fluorine-containing polymer is between 250,000 g / mol and 490,000 g / mol.

[0012] According to some embodiments, the first fluoropolymer has a first melt flow index, and the second fluoropolymer has a second melt flow index lower than the first melt flow index. The difference between the first melt flow index and the second melt flow index is 0.1 g / 10 min to 1 g / 10 min.

[0013] According to some embodiments, the first melt flow index is between 0.8 g / 10 min and 1.4 g / 10 min, and the second melt flow index is between 0.4 g / 10 min and 0.7 g / 10 min.

[0014] According to some embodiments, the first fluoropolymer is polyvinylidene fluoride.

[0015] According to some embodiments, the polymer substrate further comprises a third fluorine-containing polymer selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkylene-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, and any combination thereof.

[0016] According to some embodiments, the third fluorine-containing polymer is polytetrafluoroethylene, and based on 100% of the volume of the thermistor layer, the volume percentage of the polytetrafluoroethylene is 4% to 6%.

[0017] According to some embodiments, the polymer matrix further comprises an internal filler selected from the group consisting of barium titanate, strontium titanate, calcium titanate, and any combination thereof.

[0018] According to some embodiments, the conductive filler includes carbon black and at least one metal compound selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, and zirconium nitride.

[0019] According to some embodiments, the overcurrent protection element has a resistance change difference due to temperature shock between 0.0007Ω and 0.0021Ω. Regarding the resistance change difference due to temperature shock mentioned above: the overcurrent protection element has an initial resistance value; the overcurrent protection element has a first resistance value after 300 cycles of thermal shock at a temperature of -40°C to 85°C; and the first resistance value minus the initial resistance value is the resistance change difference due to temperature shock.

[0020] According to some embodiments, after 300 thermal shock cycles at temperatures between -40°C and 85°C, and then after 24V / 40A is applied for 3 minutes and cooled to room temperature, the overcurrent protection element has a secondary shock resistance value between 0.02Ω and 0.03Ω.

[0021] According to some embodiments, the overcurrent protection element has a first resistance jump rate between 1.43 and 1.55. Regarding the aforementioned first resistance jump rate: the overcurrent protection element has an initial resistance value; the overcurrent protection element has a second resistance value after 24V / 40A is applied for 3 minutes and cooled to room temperature; and the second resistance value divided by the initial resistance value is the first resistance jump rate.

[0022] According to some embodiments, at 24V / 40A applied, the power consumption of the overcurrent protection element is between 1.5W and 1.6W.

[0023] According to some embodiments, the overcurrent protection element has a volume resistivity between 0.03 Ω·cm and 0.04 Ω·cm.

[0024] According to some embodiments, the overcurrent protection element has a second resistance jump rate between 2.46 and 2.94. Regarding the aforementioned second resistance jump rate: the overcurrent protection element has an initial resistance value; the overcurrent protection element has a third resistance value after being cycled 100 times in the cycle life test and cooled to room temperature; and the third resistance value divided by the initial resistance value is the second resistance jump rate.

[0025] According to some embodiments, the overcurrent protection device has a trigger current thermal drop ratio between 0.6 and 0.7. The trigger current thermal drop ratio is defined as the trigger current required by the overcurrent protection device at 85°C divided by the trigger current required by the overcurrent protection device at 23°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A cross-sectional view showing an overcurrent protection element according to an embodiment of the present invention;

[0027] Figure 2 show Figure 1 A top view of an overcurrent protection element;

[0028] Figure 3 A perspective schematic diagram showing a motor; and

[0029] Figure 4 show Figure 3 Section view along line segment AA.

[0030] The reference numerals are described as follows:

[0031] 10Overcurrent protection element

[0032] 11Thermistor layer

[0033] 12 Upper metal layer

[0034] 13 Lower metal layer

[0035] 20 rotor module

[0036] 30 stator module

[0037] 41 First Wire

[0038] 42 Second wire

[0039] A Length

[0040] B Width DETAILED DESCRIPTION

[0041] In order to make the above and other technical contents, features and advantages of the present invention more clearly understood, relevant embodiments are given below and described in detail with reference to the accompanying drawings.

[0042] Please refer to Figure 1 , showing the basic state of the overcurrent protection element of the present invention. The overcurrent protection element 10 includes a thermistor layer 11 and an electrode layer. The thermistor layer 11 has an upper surface and a lower surface, and the electrode layer has an upper metal layer 12 and a lower metal layer 13 respectively attached to the upper surface and the lower surface of the thermistor layer 11. In this way, the thermistor layer 11 is physically in direct contact with the upper metal layer 12 and the lower metal layer 13, and is stacked between the two. In one embodiment, the upper metal layer 12 and the lower metal layer 13 can be composed of nickel-plated copper foil or other conductive metals. In addition, the thermistor layer 11 includes a polymer substrate and a conductive filler. The polymer substrate is an insulator that is easily expanded by heat, and the conductive filler is a conductor, so that the thermistor layer 11 has a positive temperature coefficient characteristic. When the overcurrent protection element 10 is not triggered, the conductive filler is evenly dispersed in the polymer matrix and connected in series to form a conductive channel; when the overcurrent protection element 10 is affected by high temperature, the polymer matrix will expand rapidly, causing the conductive filler particles to be pulled apart, resulting in the truncation of the conductive channel. It can be seen that before triggering, the thermal stability of the polymer matrix and the type of conductive filler determine the size of the holding current (I-hold) of the overcurrent protection element.

[0043] In the present invention, the main component of the polymer matrix includes two fluorine-containing polymers, namely a first fluorine-containing polymer and a second fluorine-containing polymer. The first fluorine-containing polymer can be polyvinylidene fluoride, which has a relatively low weight average molecular weight (MW). w), which is between 250,000 g / mol and 490,000 g / mol. The second fluoropolymer is a fluoropolymer with the same or similar skeleton as the first fluoropolymer, and has a higher weight average molecular weight, which is between 630,000 g / mol and 1,100,000 g / mol. The first fluoropolymer and the second fluoropolymer can form an interpenetrating polymer network (IPN) structure. More specifically, traditional overcurrent protection elements only use a single type of fluoropolymer (such as polyvinylidene fluoride) as a high-protection temperature polymer matrix; if two fluoropolymers with different physicochemical properties but the same polymerization monomers (such as two polyvinylidene fluorides) are selected at the same time, there is often no significant improvement in electrical properties, or the performance is poor. Regarding the latter, the main reason lies in the complexity of the formula design. For each additional compound composition, it is necessary to consider the compatibility of the compound composition with the existing polymer matrix, conductive filler and other internal fillers. Even if the compound composition is compatible with the existing high molecular polymer matrix, conductive filler and other internal fillers, it needs to be precisely adjusted to an appropriate ratio to maintain good electrical properties, otherwise there will be the aforementioned problem of no obvious improvement or poor performance. However, the present invention notes that as long as the weight average molecular weight of the second fluoropolymer is adjusted to between 630,000 g / mol and 1,100,000 g / mol and supplemented with an appropriate ratio, the thermal stability of the resistor can be effectively improved and a lower volume resistivity (about 0.03 Ω·cm to 0.04 Ω·cm) can be maintained. In one embodiment, the weight average molecular weight of the second fluoropolymer is between 730,000 g / mol and 1,000,000 g / mol. In another embodiment, the weight average molecular weight of the second fluoropolymer is between 800,000 g / mol and 900,000 g / mol. In a preferred embodiment, the weight average molecular weight of the second fluoropolymer is 880,000 g / mol. As for the above-mentioned appropriate proportion, with the volume of the thermistor layer as 100%, the volume percentage of the first fluoropolymer is 12% to 42%, and the volume percentage of the second fluoropolymer is 1% to 31%. The content of the first fluoropolymer can be greater than, equal to or less than the content of the second fluoropolymer. It should be noted that the upper limit value (31%) of the content of the second fluoropolymer will be lower than the upper limit value (42%) of the content of the first fluoropolymer. Because the second fluoropolymer has a much higher weight average molecular weight than the first fluoropolymer, if the ratio is too high, the material of the thermistor layer 11 will be difficult to flow during production, which is not conducive to mixing. Therefore, if the content of the first fluoropolymer is greater than or equal to the content of the second fluoropolymer, this will help the mixing between the polymer and the conductive filler, so as to facilitate the manufacture of the thermistor layer 11.In a preferred embodiment of the present invention, the volume percentage of the first fluorine-containing polymer is 22% to 37%, and the volume percentage of the second fluorine-containing polymer is 6% to 22%.

[0044] In addition, the present invention further notes that the second fluorine-containing polymer can have similar effects as long as it has the core skeleton of the first fluorine-containing polymer. More specifically, if the first fluorine-containing polymer is polyvinylidene fluoride, the chemical structure of the second fluorine-containing polymer is as shown in formula (I):

[0045]

[0046] In formula (I), the repeating unit of the second fluorine-containing polymer has a core skeleton of -CH2CF2-, which connects two functional groups (i.e., R1 and R2). R1 ​​and R2 are both selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4, and R1 and R2 are different. For example, when R1 is CH2, R2 is selected from the group consisting of CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4. In addition, n is the number of repeating units, which is at least 9000. In one embodiment, the second fluorine-containing polymer can also be polyvinylidene fluoride, so R1 is CF2 and R2 is CH2.

[0047] More advantageously, the difference in fluidity between the first fluoropolymer and the second fluoropolymer of the present invention can be adjusted to an appropriate range. The aforementioned difference in fluidity can be explained by the melt flow index. The melt flow index refers to the number of grams of melt that flows through a standard capillary tube at a specific temperature every ten minutes, which can be used to evaluate the fluidity of the polymer in a molten state. According to the standard specification of ASTM D1238, at a temperature of 230°C, the first fluoropolymer has a first melt flow index, and the second fluoropolymer has a second melt flow index lower than the first melt flow index. The difference between the first melt flow index and the second melt flow index (also called the melt flow index difference) is 0.1g / 10min to 1g / 10min. In one embodiment, the melt flow index difference may be 0.5g / 10min to 1g / 10min. In another embodiment, the melt flow index difference may be 0.5 g / 10min, 0.6 g / 10min, 0.7 g / 10min, 0.8 g / 10min, 0.9 g / 10min or 1 g / 10min. For example, the first melt flow index may be between 0.8 g / 10min and 1.4 g / 10min, and the second melt flow index may be between 0.4 g / 10min and 0.7 g / 10min. By using the low flow characteristics of the second fluoropolymer, the high flow characteristics of the first fluoropolymer can be improved in an appropriate proportion, while the thermistor layer 11 has better electrical characteristics.

[0048] In addition, the polymer matrix of the present invention may further include a third fluoropolymer. The third fluoropolymer is selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluorocarbon oxide-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer and any combination thereof. The melting point of the third fluoropolymer is much higher than the melting points of the aforementioned first fluoropolymer and the second fluoropolymer. For example, the melting points of the first fluoropolymer and the second fluoropolymer are between 170°C and 186°C, while the melting point of the third fluoropolymer is between 320°C and 335°C. When the ambient temperature is higher than the melting points of the first fluoropolymer and the second fluoropolymer and lower than the melting point of the third fluoropolymer, the first fluoropolymer and the second fluoropolymer will melt while the third fluoropolymer will not. Accordingly, the third fluoropolymer can be present as solid particles uniformly dispersed in the thermistor layer 11 and serve as a nucleation center when the fluoropolymer recrystallizes, which is conducive to the formation of crystals. Alternatively, based on the high melting point characteristics of the third fluoropolymer, the deformation degree of the third fluoropolymer is small at high temperatures, thereby effectively stabilizing the structural form of the thermistor layer 11 without excessive deformation. In one embodiment, the third fluoropolymer is polytetrafluoroethylene, and the volume percentage of polytetrafluoroethylene is 4% to 6% based on the volume of the thermistor layer 11 being 100%.

[0049] As for the conductive filler, in addition to carbon black, it further includes at least one metal compound so that the overcurrent protection element 10 has better electrical conduction characteristics. The metal compound is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride and zirconium nitride.

[0050] In addition to the aforementioned high molecular polymer substrate and conductive filler, the thermistor layer 11 further includes an internal filler. The internal filler is selected from the group consisting of barium titanate, strontium titanate, calcium titanate and any combination thereof. More specifically, the present invention does not include conventionally selected flame retardants (such as boron nitride, aluminum nitride, aluminum oxide or magnesium hydroxide), but selects compounds with a perovskite structure (i.e., the above-mentioned barium titanate, strontium titanate and calcium titanate). These compounds have better dielectric properties, and when combined with the first fluorinated polymer and the second fluorinated polymer, the flame retardant effect is also better than that of conventional flame retardants, which can further enhance the overall voltage resistance characteristics of the overcurrent protection element 10.

[0051] In addition to the improved formula, the overcurrent protection element 10 of the present invention can also have different sizes. Figure 2 ,for Figure 1 The overcurrent protection element 10 has a length A and a width B, and the area "A×B" is also equal to the area of ​​the thermistor layer 11. The thermistor layer 11 may have a top view area of ​​4mm depending on the product model. 2 Up to 72mm 2 For example, the area "A x B" can be 2 x 2 mm 2 , 4×4mm 2 , 5×5mm 2 、5.1×6.1mm 2 , 5×7mm 2 、7.62×7.62mm 2 、8.2×7.15mm 2 、7.3×9.5mm 2 or 7.62×9.35mm 2 In addition, the overall thickness of the overcurrent protection element 10 (i.e., the sum of the thicknesses of the upper metal layer 12, thermistor layer 11, and the lower metal layer 13) is between 0.5 mm and 0.6 mm. For example, the top surface area of ​​the overcurrent protection element 10 may be 35 mm. 2 (ie 5×7mm 2 ), and the thickness is 0.55 mm. In another embodiment, the top surface area of ​​the overcurrent protection element 10 may be 25 mm 2 (ie 5×5mm 2 ), and the thickness is 0.5mm. It should be understood that the overcurrent protection element 10 of the present invention has the same effect when applied to the above dimensions. In addition, the overcurrent protection element 10 can be processed into a common component type in the industry according to needs, such as a surface-mount device (SMD), an axial-leaded device (ALD), a radial-leaded device (RLD) or other types of components.

[0052] Based on the above formula and size, the overcurrent protection element 10 of the present invention further includes several other electrical characteristics, which are described below using thermal shock test, trip jump test, cycle life test and thermal derating effect test.

[0053] In the thermal shock test, the overcurrent protection element 10 of the present invention has a resistance change difference of temperature shock between 0.0007Ω and 0.0021Ω. In detail, the condition of a single (i.e., one cycle) thermal shock is: the overcurrent protection element 10 of the present invention is placed in an environment of -40°C for 30 minutes, and then the overcurrent protection element 10 of the present invention is placed in an environment of 85°C for 30 minutes. In this way, through multiple cycles of thermal shock, the effect of alternating low temperature (-40°C) and high temperature (85°C) (i.e., temperature shock) on the resistance value of the overcurrent protection element 10 of the present invention can be evaluated. As for the resistance change difference of temperature shock mentioned above, it refers to the resistance value change before and after the thermal shock test. More specifically, the overcurrent protection element 10 of the present invention has an initial resistance value before any test; the overcurrent protection element 10 of the present invention has a first resistance value after 300 cycles of thermal shock at a temperature of -40°C to 85°C; and the first resistance value minus the initial resistance value is the resistance change difference of temperature shock. Under the same conditions, the resistance change difference of the temperature shock of the traditional overcurrent protection element will be at least greater than 0.004Ω, which is much greater than the upper limit value of the resistance change difference of the temperature shock of the present invention (0.0021Ω). Obviously, the overcurrent protection element 10 of the present invention can maintain good resistance stability in the untriggered temperature section without affecting the flow of current. In addition, in order to further confirm the resistance stability of the overcurrent protection element 10 of the present invention, the present invention applies another shock (i.e., applies a specific power) to the overcurrent protection element 10 after the cold and hot shock. In detail, after 300 cycles of cold and hot shocks at a temperature of -40°C to 85°C, and then after 24V / 40A is applied for 3 minutes and cooled to room temperature, the overcurrent protection element 10 of the present invention has a secondary shock resistance value between 0.02Ω and 0.03Ω. In contrast, the resistance value of the secondary shock of the traditional overcurrent protection element is at least greater than 0.34Ω. From the foregoing, it can be further determined that the overcurrent protection element 10 of the present invention can still maintain good resistance stability under different pressure conditions (such as temperature and withstand power). It is worth mentioning that the stability of the resistance value of the overcurrent protection element when it is not triggered is particularly important and has strict requirements for certain industries, such as motors in the automotive market. Please continue to refer to Figure 3 and Figure 4 .

[0054] Figure 3 A three-dimensional schematic diagram showing the basic components of a motor is shown. Figure 4 Along Figure 3The AA line segment of the motor shows its cross-sectional view. The motor generally includes a rotor module 20, a stator module 30 and an electrical connection end (a first wire 41 and a second wire 42). The rotor module 20 has a rotating shaft, a rotor core, a rotor winding and other components (not shown). The stator module 30 has a stator core, a stator winding, a brush and other non-rotating components (not shown). The external power supply can be continuously supplied to the motor through the electrical connection end. When current flows through the stator module 30, the stator winding in the stator module 30 generates a rotating magnetic field, and the rotor winding in the rotor module 20 generates an opposite induced magnetic field correspondingly, and the interaction between the two drives the rotation of the rotor. Under normal circumstances, as the external power supply is continuously supplied to the stator module 30, the rotor module 20 will continue to rotate accordingly, thereby driving the operation of the external components connected to the motor. However, when the motor load is too large, the external machinery to be driven fails or the bearing is damaged, etc., the motor may be blocked. That is, the rotor module 20 stops rotating, while the stator module 30 continues to receive the external power supply. In this case, in order to drive the rotor module 20 to rotate, the current flowing through the stator module 30 (i.e. the stall current) will be much larger than the current before the stall, which may cause the winding to burn out if it lasts for a long time. Figure 4 As shown, the overcurrent protection element 10 of the present invention can be installed at the bottom of the housing of the stator module 30 to prevent the motor from being damaged. When the motor is blocked and causes a large current or excessive temperature, the overcurrent protection element 10 can be triggered to a high resistance state in time to cut off the current flow between the external power supply and the stator module 30. Moreover, more importantly, when the motor is not blocked, the overcurrent protection element 10 can maintain a stable low resistance state under the high temperature generated when the motor is running, which will not affect the normal operation of the motor and maintain good driving quality.

[0055] In the specific power triggering test, the overcurrent protection element 10 of the present invention has a first resistance jump rate between 1.43 and 1.55. Specifically, the overcurrent protection element 10 of the present invention has an initial resistance value before any test, and has a second resistance value after 24V / 40A is applied for 3 minutes and cooled to room temperature. The second resistance value divided by the initial resistance value is the first resistance jump rate. The overcurrent protection element 10 of the present invention can be triggered by the continuous application of a specific power (24V / 40A). In this way, the first resistance jump rate can evaluate the resistance recovery ability of the overcurrent protection element 10 of the present invention after at least one triggering. In contrast, the first resistance jump rate of the conventional overcurrent protection element is at least 1.58, which is higher than the upper limit value of the first resistance jump rate of the overcurrent protection element 10 of the present invention (i.e., 1.55), indicating that the resistance recovery ability of the overcurrent protection element 10 of the present invention is better and can be restored to a lower resistance state after being triggered. In addition, when the overcurrent protection element 10 is triggered, because the current cannot be completely cut off, there will still be leakage current passing through. The energy consumption can be calculated according to the magnitude of the leakage current. The energy consumption of the overcurrent protection element 10 of the present invention is between 1.5W and 1.6W, while the energy consumption of the conventional overcurrent protection element is at least 1.63. It can be seen that the overcurrent protection element 10 of the present invention has better resistance recovery capability and has the advantage of low energy consumption.

[0056] In the cycle life test, the overcurrent protection element 10 of the present invention has a second resistance jump rate between 2.46 and 2.94. Specifically, the overcurrent protection element 10 of the present invention has an initial resistance value before any test, and has a third resistance value after 100 cycles of the cycle life test and cooling to room temperature. The third resistance value divided by the initial resistance value is the second resistance jump rate. The conditions of the aforementioned cycle life test are 36V / 30A voltage / current applied for 10 seconds, and then closed for 60 seconds as one cycle. In this way, 100 cycles are repeated. The cycle life test can not only evaluate the durability of the overcurrent protection element 10 of the present invention (i.e. whether it will burn out), but also evaluate its resistance recovery ability after multiple triggering through the second resistance jump rate. In contrast, the traditional overcurrent protection element will burn out in the aforementioned cycle life test, and the second resistance jump rate is not calculated accordingly, indicating that the overcurrent protection element 10 of the present invention has better durability and better resistance recovery ability.

[0057] In the thermal drop effect test, the overcurrent protection element 10 of the present invention has a trigger current thermal drop ratio between 0.6 and 0.7. Specifically, the trigger current thermal drop ratio is defined as the trigger current required by the overcurrent protection element 10 in an environment of 85°C divided by the trigger current required by the overcurrent protection element 10 in an environment of 23°C. The thermal drop effect test is used to compare the difference in the trigger current of the overcurrent protection element 10 of the present invention under different ambient temperatures, thereby evaluating the impact of high temperature on operability. Ideally, it is expected that the trigger current of the overcurrent protection element 10 of the present invention can be maintained at the same value under various temperatures, stabilized at the preset trigger current to play a protective role, and facilitate operation. In contrast, the trigger current thermal drop ratio of the conventional overcurrent protection element is lower than 0.6, which means it is lower than the lower limit of the trigger current thermal drop ratio of the overcurrent protection element 10 of the present invention. It can be seen from this that the current required for the overcurrent protection element 10 of the present invention to be triggered is less affected by temperature, and can be stabilized at the preset trigger current to play a protective role, which is convenient for operation.

[0058] As described above, the present invention can make the overcurrent protection element 10 have good electrical characteristics at high temperatures. The following Tables 1 to 6 further illustrate the actual verification data.

[0059] Table 1. Main polymers of polymer matrix

[0060] polymer Melt flow index (g / 10min) Melting point(℃) PVDF-1 1.1 185 PVDF-2 0.55 171 PVDF-3 3 168

[0061] Table 2. Ratio of thermistor layer (vol%)

[0062] Group PVDF-1 PVDF-2 PVDF-3 PTFE BaTiO3 CB WC E1 41 2 5 10 2 40 E2 37 6 5 10 2 40 E3 29 14 5 10 2 40 E4 22 22 5 10 2 40 E5 14 29 5 10 2 40 C1 43 0 5 10 2 40 C2 0 0 43 5 10 2 40 C3 0 14 29 5 10 2 40

[0063] As shown in Table 1, the main polymer types used in the polymer matrix are three types of polyvinylidene difluoride (PVDF), which can also be referred to as the first polyvinylidene fluoride (PVDF-1), the second polyvinylidene fluoride (PVDF-2) and the third polyvinylidene fluoride (PVDF-3). In terms of melting point, the melting points of PVDF-1, PVDF-2 and PVDF-3 are 185°C, 171°C and 168°C, respectively. The melt flow index is measured according to the standard specification of ASTM D1238. Among the three, PVDF-2 has the lowest melt flow index of 0.55g / 10min. In addition, the weight average molecular weight of PVDF-1 is 350,000g / mol; the weight average molecular weight of PVDF-2 is 880,000g / mol; and the weight average molecular weight of PVDF-3 is 290,000g / mol. PVDF-2 has a higher weight average molecular weight, which not only reduces the flow characteristics of the material itself, but also means that this polyvinylidene fluoride contains a higher proportion of α phase structure. It should be understood that polyvinylidene fluoride has multiple crystal phases (such as α phase, β phase, γ phase, δ phase and ε phase), among which α phase polyvinylidene fluoride has the most stable structure.

[0064] Continuing to refer to Table 2, Table 2 shows the formula ingredients of thermistor layer of each embodiment of the present invention (Group E1 to Group E5) and comparative examples (Group C1 to Group C3) in volume percentage. The first column shows each group from top to bottom, namely, Embodiment E1 to Comparative Example C3. The first row shows the various material ingredients of thermistor layer from left to right, namely polyvinylidene fluoride (PVDF-1, PVDF-2 and PVDF-3), polytetrafluoroethylene (Polytetrafluoroethylene, PTFE), barium titanate (Bariumtitanate, BaTiO3), carbon black (Carbon black, CB) and tungsten carbide (Tungsten carbide, WC). Each group uses barium titanate to replace the flame retardant (such as magnesium hydroxide) traditionally used in overcurrent protection components. As for the conductive filler, in order to improve the conductivity of the component, tungsten carbide is mainly used, and carbon black is secondary. The combination of tungsten carbide and carbon black can generally be called a low volume resistivity conductive filler.

[0065] In Examples E1 to E5 of the present invention, the main component of the polymer matrix is ​​composed of two PVDFs (PVDF-1 and PVDF-2), and the secondary component is PTFE. Since PTFE has a much higher melting point than PVDF (about 330°C), the proportion of PTFE should not be too large to avoid affecting the processability and triggering characteristics of the overcurrent protection element. In other words, the relative proportion of PVDF and PTFE must be appropriately adjusted. However, it should be noted that the main component of the polymer matrix has two PVDFs with different physical and chemical properties, rather than a single type of PVDF, so the complexity of the formula design is greater. After testing, the optimal ratio of PVDF:PTFE obtained by the present invention is about 9:1. Therefore, in the formula of Table 2, the total volume percentage of PVDF-1 and PVDF-2 is about 43%, and the volume percentage of PTFE is 5%. It is understood that, considering the content error in the formulation, the allowable error of the main components (PVDF-1 and PVDF-2) of the polymer matrix is ​​about 5%, and the same technical effect is achieved in practical applications. For example, the total volume percentage of PVDF-1 and PVDF-2 can be about 48%; according to the ratio of Example E1 of the present invention, PVDF-1 accounts for about 46%, and PVDF-2 accounts for about 2%; according to the ratio of Example E2 of the present invention, PVDF-1 accounts for about 41%, and PVDF-2 accounts for about 7%; according to the ratio of Example E3 of the present invention, PVDF-1 accounts for about 32%, and PVDF-2 accounts for about 16%; according to the ratio of Example E4 of the present invention, PVDF-1 accounts for about 24%, and PVDF-2 accounts for about 24%; according to the ratio of Example E5 of the present invention, PVDF-1 accounts for about 16%, and PVDF-2 accounts for about 32%. Alternatively, the total volume percentage of PVDF-1 and PVDF-2 may be about 38%, and the ratio of PVDF-1 and PVDF-2 can be deduced based on the above-mentioned category.

[0066] In Comparative Examples C1 to C3, the main component of the polymer substrate is PVDF, and the minor component is PTFE. The main components of the polymer substrates of Comparative Examples C1 and C2 are both composed of a single PVDF, while the main component of the polymer substrate of Comparative Example C3 is composed of two PVDFs (i.e., PVDF-2 and PVDF-3). Traditionally, a single PVDF (i.e., Comparative Examples C1 and C2) is often used to improve overcurrent protection elements, but the electrical characteristics are not good; even if two PVDFs (Comparative Example C3) are used to improve overcurrent protection elements, the same problem still exists. Subsequent experiments will show that Examples E1 to E5 of the present invention are superior to Comparative Examples C1 to C3 in performance.

[0067] The manufacturing process of the overcurrent protection element of Examples E1 to E5 of the present invention and Comparative Examples C1 to C3 is described as follows. First, based on the formula presented in Table 1, the materials in the formula are added to a twin-screw mixer produced by HAAKE for mixing. The mixing temperature is set to 215°C, the premixing time is 3 minutes, and the mixing time is 15 minutes. After mixing, a conductive polymer can be obtained and a hot press is used at 210°C and 150kg / cm 2 The sheet was then cut into squares of about 20 cm x 20 cm. Then, the hot press was used again at 210°C and 150 kg / cm 2 The two nickel-plated copper foils are pressed onto the two sides of the conductive polymer sheet with a pressure of 100° to form a three-layer plate. Finally, a punch is used to punch out multiple chips from the plate, which are the overcurrent protection components. The length and width of the overcurrent protection component are 5mm and 7mm respectively (i.e., the top surface area is 35mm). 2 ), and the thickness is 0.55 mm. Then, after the wafers prepared in the embodiment and the comparative example were irradiated with a light dose of 150 kGy (the light dose can be adjusted according to the needs and is not a limiting condition of the present invention), 15 wafers were taken as test samples for subsequent tests.

[0068] Tables 3 to 6 show the test data of the thermal shock test, the specific power trigger test, the cycle life test and the thermal drop effect test respectively.

[0069] Table 3. Thermal shock test

[0070]

[0071] As shown in Table 3, the first column shows the verification items from left to right.

[0072] R i , refers to the initial resistance value of the overcurrent protection element at room temperature.

[0073] R 300C , refers to the resistance value of the overcurrent protection element after 300 cycles of thermal shock at a temperature of -40°C to 85°C and then cooling to room temperature. 300C Minus R i The difference obtained is Delta R. Delta R is the difference in resistance change due to the aforementioned temperature shock.

[0074] R 300C_trip , refers to the resistance value of the overcurrent protection element after the aforementioned thermal shock cycle, then 24V / 40A is applied for 3 minutes and cooled to room temperature. 300C_trip Divide by R 300C Then we can get R jump .

[0075] In Embodiments E1 to E5 of the present invention, R i is 0.00520Ω to 0.00621Ω, and R 300C In contrast, in Comparative Examples C1 to C3, R i 0.00546Ω to 0.01003Ω, and R 300C From the above, it can be seen that, compared with Comparative Examples C1 to C3, the initial resistance values ​​(R i ) is maintained in a relatively low range. After the thermal shock, the difference in resistance value is more obvious. 300C The R 300C . Further comparing the changes in resistance value before and after, it can be found that the Delta R of Examples E1 to E5 of the present invention is 0.00070Ω to 0.00204Ω, while the Delta R of Comparative Examples C1 to C3 is 0.00466Ω to 0.01050Ω. The difference in resistance change due to temperature shock of Comparative Examples C1 to C3 is at least twice that of Examples E1 to E5 of the present invention, indicating that the resistance value of Examples E1 to E5 of the present invention before being triggered is relatively insensitive to the ambient temperature. In this way, the resistance value of Examples E1 to E5 of the present invention has better thermal stability and can maintain a stable large current before the overcurrent protection element 10 is triggered.

[0076] To further verify the resistance stability of the embodiments E1 to E5 of the present invention, a specific power is applied to trigger the overcurrent protection element after the thermal shock (i.e., the aforementioned 24V / 40A is applied for 3 minutes). That is, after the temperature shock, a specific power shock is applied again to observe the resistance stability of the overcurrent protection element under the two types of shocks. As shown in Table 3, the R 300C_trip is 0.02267Ω to 0.02972Ω, while the R 300C_trip The R of the embodiments E1 to E5 of the present invention is 0.03472Ω to 0.06885Ω. 300C_trip The R 300C_trip Moreover, the difference between the two can be up to 3 times (such as Example E3 of the present invention and Comparative Example C3). The above results show that even if Examples E1 to E5 of the present invention are subjected to a variety of different pressure shocks, they can still maintain good resistance stability.

[0077] Table 4. Specific power trigger test

[0078]

[0079] As shown in Table 4, the first column shows the verification items from left to right.

[0080] R i , refers to the initial resistance value of the overcurrent protection element at room temperature.

[0081] R trip , refers to the resistance value of the overcurrent protection element after 24V / 40A is applied for 3 minutes and cooled to room temperature. Based on this, R trip / R i , which is the first resistance jump rate mentioned above.

[0082] Energy consumption is the product of leakage current and applied voltage. Based on this, energy consumption per unit area can be further calculated.

[0083] In Embodiments E1 to E5 of the present invention, R i is 0.00510Ω to 0.00590Ω, and R trip In contrast, in Comparative Examples C1 to C3, R i 0.00540Ω to 0.01010Ω, and R trip From the above, it can be seen that compared with Comparative Examples C1 to C3, the R i and R trip All remain in a relatively low range. Further analysis of R trip The resistance jump degree (i.e. R trip / R i ), the difference is more significant. Specifically, R of Examples E1 to E5 of the present invention trip / R i The R trip / R i Even though comparative example C3 has the most stable resistance state among all comparative examples, its R trip / R i Still higher than all the embodiments E1 to E5 of the present invention. Moreover, the embodiments E1 to E5 of the present invention also have better performance in current cutoff. Compared with the comparative examples C1 to C3, the leakage current of the embodiments E1 to E5 of the present invention is smaller, so the energy consumption can be maintained at a lower level (1.52W to 1.6W).

[0084] Table 5. Cycle life test

[0085]

[0086] It should be noted that the cycle life test used in this experiment has three sets of different powers and cycle numbers (hereinafter referred to as the first cycle life test, the second cycle life test and the third cycle life test). The power of the first cycle life test is 24V / 40A and the number of cycles is 500; the power of the second cycle life test is 30V / 30A and the number of cycles is 300; and the power of the third cycle life test is 36V / 30A and the number of cycles is 100.

[0087] As shown in Table 5, the first column shows the verification items from left to right.

[0088] R i , refers to the initial resistance value of the overcurrent protection element at room temperature. In addition, according to the volume resistivity formula ρ=R×A / L, R is the resistance value, L is the thickness, and A is the area. i The volume resistivity is calculated as ρ.

[0089] R 500C , refers to the resistance value of the overcurrent protection element when it is cooled to room temperature after the first cycle life test. R 300C , refers to the resistance value of the overcurrent protection element when it is cooled to room temperature after the second cycle life test. R 100C , refers to the resistance value of the overcurrent protection element when it is cooled to room temperature after the third cycle life test. R 100C / R i Then it is the second resistance jump rate.

[0090] R of Examples E1 to E5 of the present invention i is 0.0053Ω to 0.0062Ω, while the R i The volume resistivity is calculated according to the above formula. The volume resistivity (ρ) of Examples E1 to E5 of the present invention is 0.0335 Ω·cm to 0.0393 Ω·cm, while the volume resistivity (ρ) of Comparative Examples C1 to C3 is 0.0339 Ω·cm to 0.0671 Ω·cm. Similarly, relative to Comparative Examples C1 to C3, the initial resistance values ​​(R i) and volume resistivity (ρ) are maintained in a relatively low range, and have better electrical conduction capability. In the cycle life test, embodiments E1 to E5 of the present invention can pass the first cycle life test and the second cycle life test without burning. As for the third cycle life test, only embodiments E2 to E5 of the present invention pass without burning, while embodiment E1 of the present invention burns. 100C The embodiments E2 to E5 of the present invention can withstand the high voltage and high power of the third cycle life test, and calculate the second resistance jump rate (R 100C / R i ) is between 2.46 and 2.94. In contrast, all of Comparative Examples C1 to C3 fail to pass the first cycle life test, the second cycle life test, and the third cycle life test. In other words, Comparative Examples C1 to C3 will burn out in the first cycle life test, the second cycle life test, and the third cycle life test, so R cannot be obtained accordingly. 500C , R 300C and R 100C data. It should also be mentioned that Comparative Examples C1 and C3 have not burned out at the 300th cycle of the first cycle life test, but their resistance values ​​have climbed to 0.0315Ω and 0.07177Ω respectively, which are much higher than the resistance values ​​of all embodiments E1 to E5 of the present invention at the 500th cycle. In addition, Comparative Examples C2 and C3 will burn out at 100 cycles of the second cycle life test, and they have burned out before even half of the preset number of cycles (300 cycles) is reached. In any case, Comparative Examples C1 to C3 not only have high volume resistivity, but also have poor withstand voltage characteristics.

[0091] Table 6. Thermal drop effect test

[0092]

[0093] As shown in Table VI, the first column shows the verification items from left to right.

[0094] IT 23℃ and IT 85℃ , respectively, refer to the trigger current of the overcurrent protection element at 23℃ and 85℃. Based on this, IT can be calculated accordingly 23℃ / area and IT 85℃ / area, that is, the size of the trigger current per unit area.

[0095] IT 85℃ / IT 23℃This is the trigger current thermal drop ratio defined above. As mentioned above, the current required to trigger the overcurrent protection element will be different at different ambient temperatures. In a low temperature environment, the overcurrent protection element has a lower resistance value, and the current required to trigger will be relatively large. In a high temperature environment, the overcurrent protection element has a higher resistance value, and the current required to trigger will be relatively small. Therefore, the trigger current thermal drop ratio (IT 85℃ / IT 23℃ ) can be used to evaluate the effect of temperature rise on the operability of the overcurrent protection element. The trigger current thermal drop ratio (IT) of the embodiments E1 to E5 of the present invention is 85℃ / IT 23℃ ) is 0.615 to 0.665, while the trigger current thermal drop ratio (IT) of Comparative Examples C1 to C3 is 85℃ / IT 23℃ ) is 0.444 to 0.592. Obviously, the trigger current heat drop ratio (IT 85℃ / IT 23℃ ) is closer to 1, which means that the trigger current is relatively stable under different ambient temperatures. 85℃ / IT 23℃ ) can be as low as 0.444, which means that the trigger current has dropped by more than half in an environment of 85°C, which is quite unstable. From the above, it can be seen that, at an untriggered ambient temperature, the embodiments E1 to E5 of the present invention can play a relatively stable protective role, which is convenient for operation.

[0096] The technical content and technical features of the present invention have been disclosed as above, but a person skilled in the art with ordinary knowledge may still make various substitutions and modifications based on the teachings and disclosures of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to those disclosed in the embodiments, but should include various substitutions and modifications without departing from the present invention, and be covered by the following claims.

Claims

1. An overcurrent protection element, comprising: an electrode layer having an upper metal layer and a lower metal layer; and A thermistor layer contacts the upper metal layer and the lower metal layer and is stacked therebetween, wherein the thermistor layer has a positive temperature coefficient characteristic and comprises: A polymer matrix comprising a first fluorine-containing polymer and a second fluorine-containing polymer, wherein the weight average molecular weight of the second fluorine-containing polymer is between 630,000 g / mol and 1,100,000 g / mol; and A conductive filler is dispersed in the high molecular polymer matrix to form a conductive channel of the thermistor layer. 2 . The overcurrent protection element according to claim 1 , wherein based on 100% of the volume of the thermistor layer, the volume percentage of the first fluorine-containing polymer is 12% to 42%, and the volume percentage of the second fluorine-containing polymer is 1% to 31%.

3. The overcurrent protection element according to claim 1, wherein the second fluorine-containing polymer is represented by the following formula (I): in: R1 and R2 are selected from the group consisting of CH2, CF2, CHF, C2HF3, C2H2F2, C2H3F, C2H4 and C2F4; R1 is different from R2; and n is at least 9000. 4 . The overcurrent protection device according to claim 1 , wherein a weight average molecular weight of the first fluorine-containing polymer is between 250,000 g / mol and 490,000 g / mol.

5. The overcurrent protection element according to claim 1, wherein the first fluoropolymer has a first melt flow index, and the second fluoropolymer has a second melt flow index lower than the first melt flow index, and the difference between the first melt flow index and the second melt flow index is 0.1 g / 10 min to 1 g / 10 min. 6 . The overcurrent protection device according to claim 5 , wherein the first melt flow index is between 0.8 g / 10 min and 1.4 g / 10 min, and the second melt flow index is between 0.4 g / 10 min and 0.7 g / 10 min. The overcurrent protection device as claimed in claim 1 , wherein the first fluorine-containing polymer is polyvinylidene fluoride.

8. The overcurrent protection device according to claim 1, wherein the high molecular polymer substrate further comprises a third fluorine-containing polymer selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, perfluoroalkylene-modified tetrafluoroethylene, poly(chlorotri-fluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluorodioxole copolymer, difluoroethylene-hexafluoropropylene copolymer, difluoroethylene-hexafluoropropylene-tetrafluoroethylene terpolymer and any combination thereof. 9 . The overcurrent protection device according to claim 8 , wherein the third fluorine-containing polymer is polytetrafluoroethylene, and based on the volume of the thermistor layer being 100%, the volume percentage of polytetrafluoroethylene is 4% to 6%. 10 . The overcurrent protection device according to claim 1 , wherein the high molecular polymer matrix further comprises an internal filler selected from the group consisting of barium titanate, strontium titanate, calcium titanate and any combination thereof.

11. The overcurrent protection element according to claim 1, wherein the conductive filler comprises carbon black and at least one metal compound, and the metal compound is selected from the group consisting of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride and zirconium nitride.

12. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a temperature shock resistance change difference between 0.0007Ω and 0.0021Ω, wherein: The overcurrent protection element has an initial resistance value; The overcurrent protection element has a first resistance value after being subjected to 300 thermal shock cycles at a temperature of -40°C to 85°C; and The first resistance value minus the initial resistance value is the resistance change difference of the temperature shock.

13. The overcurrent protection element according to claim 12, wherein after being subjected to 300 thermal shock cycles at a temperature of -40°C to 85°C, and then being applied with 24V / 40A for 3 minutes and cooled to room temperature, the overcurrent protection element has a secondary shock resistance value between 0.02Ω and 0.03Ω.

14. The overcurrent protection device according to claim 1, wherein the overcurrent protection device has a first resistance jump rate between 1.43 and 1.55, wherein: The overcurrent protection element has an initial resistance value; The overcurrent protection element has a second resistance value after being applied with 24V / 40A for 3 minutes and cooled to room temperature; and The second resistance value divided by the initial resistance value is the first resistance jump rate. 15 . The overcurrent protection element according to claim 14 , wherein under the application of 24V / 40A, the energy consumption of the overcurrent protection element is between 1.5W and 1.6W. 16 . The over-current protection device as claimed in claim 1 , wherein the over-current protection device has a volume resistivity between 0.03 Ω·cm and 0.04 Ω·cm.

17. The overcurrent protection device according to claim 16, wherein the overcurrent protection device has a second resistance jump rate between 2.46 and 2.94, wherein: The overcurrent protection element has an initial resistance value; The overcurrent protection element has a third resistance value after being subjected to a cycle life test for 100 times and cooled to room temperature; and The third resistance value divided by the initial resistance value is the second resistance jump rate.

18. The overcurrent protection element according to claim 1, wherein the overcurrent protection element has a trigger current thermal drop ratio between 0.6 and 0.7, wherein the trigger current thermal drop ratio is defined as the trigger current required by the overcurrent protection element in an environment of 85°C divided by the trigger current required by the overcurrent protection element in an environment of 23°C.

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