Self-limiting heater

Abstract

A self-limiting heater and a method for constructing a self-limiting heater are disclosed. The self-limiting heater includes a resistor and a PTC resistor coupled together in series with a power source. Both resistive devices have good thermal coupling. The resistor has a minimum resistance change with temperature change, while the PTC resistor has an increasing resistance with temperature increase. The ratio of ohmic resistance between the resistor and the PTC can be used to adjust heater characteristics and limit feature sharpness.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 981,650 entitled “Self-limiting Heater”, filed February 26, 2020, which is incorporated herein by reference in its entirety. Background Technology

[0003] Positive Temperature Coefficient (PTC) devices are made of materials with an initial resistance that responds to temperature. As the temperature of the PTC device increases, its resistance also increases. When the current flowing through the PTC element increases above a predefined limit, the PTC element may heat up, causing its resistance to increase and significantly reducing or preventing current flow through the protected device. This prevents damage that would otherwise be caused by severe fault currents flowing through the circuit.

[0004] PTC devices exhibit relatively low stability in terms of lifespan and temperature, making them unsuitable for heating applications. PTC heating devices with high temperature coefficients rapidly reduce their power dissipation even with small temperature changes. Therefore, the efficiency of heaters using such PTC devices will be limited. PTC devices with low temperature coefficients will not have steep temperature limiting characteristics.

[0005] In light of these and other considerations, this improvement may be useful. Summary of the Invention

[0006] This overview is provided to introduce, in a simplified form, some concepts that will be further described in the detailed description below. This overview is not intended to identify key or essential features of the claimed subject matter, nor is it intended to assist in determining the scope of the claimed subject matter.

[0007] An exemplary embodiment of a self-limiting heating device according to the present disclosure may include a voltage source, a resistor including a minimum resistance variation with temperature, and a positive temperature coefficient (PTC) resistor, wherein the resistor and the PTC resistor are coupled in series with each other and thermally coupled to each other, wherein the self-limiting heater automatically reduces its power output in response to reaching a predefined power output.

[0008] An exemplary embodiment of a method for manufacturing a self-limiting heating device according to the present disclosure may include: coupling a resistive element to a copper layer of a metal-based substrate printed circuit board (PCB); coupling a positive temperature coefficient (PTC) element to the metal-based substrate PCB, wherein the resistive element and the PTC element are connected in series with each other; coupling a power supply including a first terminal and a second terminal to the copper layer of the metal-based substrate PCB, wherein the first terminal is coupled to the resistive element and the second terminal is coupled to the PTC element, wherein the temperature of the metal-based substrate PCB increases in response to a voltage supplied from the power supply, and wherein the temperature of the self-limiting heater does not exceed a predefined temperature. Attached Figure Description

[0009] Figure 1 This is a schematic diagram showing a circuit diagram of a self-limiting heater according to an exemplary embodiment.

[0010] Figure 2A and Figure 2B These are top and side views of a self-limiting heater on a metal-based substrate PCB according to an exemplary embodiment.

[0011] Figure 3A and Figure 3B This is a schematic diagram illustrating a thermal coupling method for the self-limiting heater of FIG2, according to an exemplary embodiment.

[0012] Figure 4 This is a graph illustrating the power characteristics of a PTC device according to an exemplary embodiment.

[0013] Figures 5A-5D The graph shown in Figure 2 illustrates the power characteristics of the self-limiting heater according to an exemplary embodiment.

[0014] Figure 6 This is a schematic diagram showing a top view and a cross-sectional view of a self-limiting heater on a metal-based substrate PCB according to an exemplary embodiment.

[0015] Figure 7 This is a schematic diagram illustrating test data for a self-limiting heater according to an exemplary embodiment. Detailed Implementation

[0016] A self-limiting heater and a method for constructing it are disclosed. The self-limiting heater comprises a resistor and a PTC resistor coupled in series with a power source. Both resistive devices exhibit good thermal coupling. The resistor has a minimal resistance change with temperature, while the resistance of the PTC resistor increases with increasing temperature. The resistance ratio of the resistor to the PTC resistor is chosen to ensure that some limitations of the PTC resistor are avoided.

[0017] Self-limiting means that the heater limits its heating power output. The self-limiting capability of a heater can mean that the power to the heater is cut off or significantly reduced (to near zero power). Alternatively, self-limiting can mean that the power is reduced to a predefined limit.

[0018] Figure 1 This is a representative diagram of a circuit 100 having a resistor element 102 coupled to a PTC element 104 according to an exemplary embodiment. Circuit 100, also referred to herein as a resistive heating device 100, will be described in more detail below. The resistor element 102 of circuit 100 is electrically connected in series to the PTC element 104. Although a single resistor element 102 and a single PTC element 104 are shown, multiple resistor elements and / or PTC elements may be present in circuit 100. Hereinafter, these elements will be referred to as “resistor 102” and “PTC 104”, respectively. A power supply 106 is coupled to the resistor 102 and the PTC 104, with a first terminal 108 of the power supply connected to the resistor and a second terminal 110 of the power supply connected to the PTC.

[0019] Circuit 100 represents a resistive heating device constructed using at least two resistive elements, resistor 102 and PTC 104. In an exemplary embodiment, the first resistive element ( Figure 1 Resistor 102 in the circuit has a very small resistance change with temperature; in other words, a low temperature coefficient. This means that even if the temperature of circuit 100 changes, the ohmic resistance of resistor 102 will not change significantly. In an exemplary embodiment, even if the temperature change is between -40°C and +160°C, the change in ohmic resistance will not exceed 1000 ppm per degree Celsius (°C).

[0020] The second resistive element in the resistive heating device 100 ( Figure 1 The PTC 104 in the example has a high temperature dependence on resistance and a positive temperature coefficient. In other words, as the temperature of the resistive heating device 100 changes, the resistance of the PTC 104 will also change. Furthermore, in the exemplary embodiment, as the temperature of the resistive heating device 100 increases, the resistance of the PTC 104 will also increase, and as the temperature of the resistive heating device decreases, the resistance of the PTC will decrease. In the exemplary embodiment, when the temperature change is between -40°C and +160°C, the change in ohmic resistance will vary from a few percent of its initial value to up to a thousand times its initial value.

[0021] like Figure 1As shown, resistor 102 and PTC 104 are electrically connected in series. Furthermore, in the exemplary embodiment, resistor 102 and PTC 104 have good thermal coupling to each other. This thermal coupling will be described in more detail below.

[0022] Traditionally, printed circuit boards (PCBs) have been manufactured using glass fiber materials such as FR-4. Metal-based PCBs are becoming more common for certain high-power applications. Metal-based PCBs allow heat to be dissipated from the components on the PCB. Almost any metal can be used in the manufacture of metal-based (metal-clad) PCBs. Aluminum PCBs are popular in many industries, including but not limited to, high-power power supplies and LED bulbs.

[0023] The resistive heating device according to circuit 100 can be made using a metal-based substrate PCB. Figure 2A and Figure 2B The diagram shows a top view and a side view of a resistive heating device 200 according to an exemplary embodiment. In the top view (… Figure 2A In the process, the resistive heating device 200 is disposed on a metal-based substrate or a metal-clad PCB 206, and includes resistors 202a and 202b (collectively referred to as "resistors 202") and a PTC 204 disposed between the two resistors.

[0024] Metal-based PCBs, or metal-clad PCBs, are made of metal-based stacks covered by copper foil circuit layers. The metal can be aluminum, magnesium, or combinations of materials such as aluminum-silicon alloy (Al-Mg-Si). A metal-based PCB includes: a base layer comprising a metal substrate (e.g., an aluminum-based alloy); a dielectric (thermally insulating) layer, which can be FR-4 as in conventional PCBs; and a circuit layer made of copper foil. All PCBs have at least one single metal layer, which is typically, but not limited to, copper. The substrate refers to the body of the PCB, which is metal-based. Alternatively, the substrate may be made of FR-4. Alternatively, the PCB may consist of copper inlays or may be a ceramic PCB, such as aluminum oxide or aluminum nitride. When current flows through the circuitry on the copper layer, the dielectric layer absorbs heat, which is transferred to the aluminum layer and then dissipated there. Metal-based PCBs offer significantly better heat dissipation than conventional PCBs.

[0025] Side view of the resistance heating device 200 ( Figure 2BThe diagram shows a top (circuit) layer 210, a middle (dielectric) layer 212, and a bottom (metal substrate) layer 214. The side view is not drawn to scale because the thickness of each layer can vary. FR-4 is a fairly good thermal insulator. The thinner the layer, the better the thermal coupling and power transfer between the heat source and the metal layer (aluminum) used as a heat sink. For example, the dielectric layer 212 can be as thin as 0.1 mm, while the aluminum layer can be, but is not limited to, between 0.4 and 3.2 mm thick.

[0026] In an exemplary embodiment, good thermal coupling exists between resistor 202 and PTC 204 in the resistive heating device 200, where the PCB serves as the interface for coupling the two devices. Good thermal coupling prevents heat dissipation, an uncontrolled feedback event in which a temperature rise alters conditions in a way that causes a continuous increase in temperature, potentially leading to damage to one or more components of the heated circuit / device or medium / device. In one embodiment, the thermal coupling of the resistive heating device 200 is achieved by soldering both resistor 202 and PTC 204 to a bottom metal substrate layer 214 (which may be aluminum). By soldering these devices to the aluminum substrate of the PCB 208, heat dissipation in the resistive heating device 200 is prevented.

[0027] Alternatively, in another embodiment, one of the resistive devices (PTC204) of the resistive heating device 200 is laminated between the two conductive plates using a resistive layer (e.g., a resistive film). Figure 3A and Figure 3B The process 300 is illustrated. A PTC layer 304 is laminated together with a resistive film 302 or a resistive heating element 302, wherein the laminated PTC layer is disposed between two conductor layers 306a and 306b (collectively referred to as "conductor layer 306"). The conductor layer 306 can be made of any highly conductive material (including but not limited to copper). By laminating the PTC layer 304 together with the resistive film 302 and surrounding them with the conductor layer 306, good thermal coupling between the PTC and the resistive film is achieved, thus protecting the resistive heating element 302 from heat dissipation. Figure 3B A diagram illustrating the process is provided. Good thermal coupling is achieved through direct contact between the resistive film and the PTC.

[0028] As is well known to those skilled in the art, the resistive elements of the resistive heating device 200 can be attached to the PCB 206 in various ways. Resistors 202 and PTC 204 can be chip resistors, which are soldered to the etched copper top circuit layer 210 using conventional methods. Alternatively, resistors 202 and PTC 204 can be placed on the copper layer, for example, by screen printing. Another method for creating the resistive heating device 200 can be using resistive ink. When the resistive ink is applied to the copper layer of the PCB, it forms an electrical contact between the conductive copper and the resistive ink. Soldering provides the same type of bonding between the conductive solder (which is metallic) and the resistive material. Embodiments of this disclosure are not limited thereto.

[0029] Temperature coefficient

[0030] All resistors have an associated temperature coefficient, which indicates how much the resistor's ohmic resistance drifts when the temperature deviates from an agreed-upon reference temperature. If the reference temperature of a resistor is 20 degrees Celsius and the resistor is used at 30 degrees Celsius, the resistor's ohmic resistance will change by a certain amount. Resistors with a minimum resistance change with temperature (assuming 25 ppm / °C) will not change much even with significant temperature variations, while resistors with a high temperature coefficient (e.g., 5000 ppm / °C) may experience significant changes in ohmic resistance. Therefore, resistors with a high temperature coefficient may affect the reliability of the circuit in which they reside.

[0031] As the name suggests, a PTC resistor is short for a positive temperature coefficient resistor, which also has an associated temperature coefficient. The "P" indicates that the ohmic resistance of a PTC resistor increases with increasing temperature. (In contrast, the ohmic resistance of a resistor with a negative temperature coefficient (NTC) decreases with increasing temperature.)

[0032] PTC resistors exhibit relatively low stability in terms of lifespan and temperature, making them less suitable for heating applications. Poor temperature stability means that the resistance at the same temperature can vary depending on the temperature reached. For example, suppose a heater incorporating a PTC resistor is raised from a very low temperature to 20°C. In this case, the resistance of the PTC resistor will be lower than when the same PTC unit is cooled to reach 20°C. Furthermore, the aging of the PTC unit also has an impact. Over long periods of operation, the resistance of the PTC unit will slowly drift, thus altering the power output of the heater. PTC heating units with high temperature coefficients are affected by small temperature changes and will rapidly reduce their power dissipation during temperature variations. Therefore, the effectiveness of heaters using PTC units with high temperature coefficients is limited.

[0033] A PTC device with a low temperature coefficient will not be as drastically affected by temperature changes as a PTC device with a high temperature coefficient. However, such a low temperature coefficient PTC device will not have a steep temperature limiting characteristic. Such a PTC is also ineffective because it will rapidly reduce its power output. For some applications, it is important to bring the object / device to its optimal operating temperature as quickly as possible. In those applications, the power output should be as high as possible. However, the object / device usually has limitations on how much power it can provide. A steep temperature limiting PTC device will rapidly lose its output power, and the object / device will not be heated sufficiently. On the other hand, a PTC without a steep temperature limiting characteristic may not reduce its power output but may instead cause overheating.

[0034] Figure 4 These contrasting characteristics are illustrated in graph 400. A resistive device with a steep temperature limiting characteristic loses its output power rapidly, so that the object / device containing the resistive device will not reach its maximum temperature (given by Tmax). Conversely, a resistive device without a steep temperature limiting characteristic loses its output power more slowly, and there is a risk that the object / device will exceed its maximum temperature and enter the overheating region.

[0035] Power dissipation

[0036] For the resistive heating device 200, power dissipation will depend on the total resistance of the two (or more) resistive elements and the applied voltage. Power dissipation can be calculated using the following formula:

[0037] (P=V) 2 / R sum (1)

[0038] Where P refers to the power dissipation of the heater, V is the voltage applied to the heating element, and R sum It is the total resistance of the resistive elements connected in series. Since the resistive heating device 200 has two (groups) of resistive elements, it can be mathematically represented as follows:

[0039] R sum =(∑R+∑R PTC (2)

[0040] Where R refers to the resistance of resistor 202, and R PTCThe resistance is that of the PTC 204. The resistive heating device 200 includes multiple resistors 202 connected in series, and the total resistance of the resistors is the sum of their individual resistances; similarly, in the case of multiple PTC 204s connected in series, the total resistance of the PTC 204s is the sum of their individual resistances. As is well known to those skilled in the art, the resistive heating device 200 can employ a single resistor 202 and a single PTC 204, or multiple of each.

[0041] Compared to resistor 202, PTC 204 can have a relatively low resistance at room temperature. Therefore, once voltage is applied to the resistive heating device 200, the current flowing through the two resistive elements (which are connected in series) will cause most of the power to be dissipated in resistor 202. This power dissipation will cause resistor 202 to heat up. However, because the power dissipation of PTC 204 is smaller than that of resistor 202, PTC 204 will heat up more slowly.

[0042] As mentioned above, to avoid heat dissipation, especially at low temperatures, it is essential to ensure good thermal coupling between the resistive element and the PTC element. Without good thermal coupling, resistor 202 (and PTC 204) may heat up above safe limits without the power limit being triggered by the resistive heating device 200. This could lead to hot spots in the resistive heating device 200, or worse. Because the power dissipation of resistor 202 causes PTC 204 to heat up, the resistance of the PTC will increase, resulting in an increase in the sum of the resistances of all components (Equation 2) and a decrease in power P (Equation 1).

[0043] Figures 5A-5D The power-temperature characteristics of the resistive heating device 200 in four scenarios are shown: typical ( Figure 5A Resistor 202 <PTC 204( Figure 5B Resistor 202 = PTC 204 ( Figure 5C ), and resistor 202>PTC 204 ( Figure 5D In these various scenarios, the resistance ratio between resistor 202 and PTC 204 can be changed.

[0044] Three scenarios:

[0045] ∑R>∑R PTC

[0046] At low temperatures, as long as the total resistance of the resistive elements is greater than the total resistance of the PTC elements (mathematically expressed as ∑R>∑R), PTC ()( Figure 5BIf the resistive element dissipates more power than the PTC element, and the heater temperature is much lower than the temperature limit condition, then the resistive element will generate more power dissipation, and the heater temperature will be much lower than the temperature limit condition. As the heater temperature rises, the PTC resistance increases and the total power of the heater decreases, thus causing the temperature limit to occur. The steeper the PTC characteristic curve (…), the greater the power dissipation. Figure 4 The more drastic the limiting characteristics of the heater are, the more pronounced the limiting characteristics become.

[0047] ∑R=∑R PTC

[0048] The sum of the resistances of one or more resistive elements is equal to the sum of the resistances of one or more PTC elements (mathematically expressed as ∑R=∑R). PTC ()( Figure 5C When the heater temperature is much lower than the temperature limit, one or more resistive elements will produce the same amount of power as one or more PTC elements. As the heater temperature rises and approaches the limit temperature, the PTC resistive portion begins to dominate and the limit condition occurs. The difference in this scenario is that the limit condition is not as pronounced as in ∑R>∑R PTC Scene ( Figure 5B It is as rapid as in (the text).

[0049] ∑R<∑R PTC

[0050] When the sum of the resistances of one or more resistive elements is less than the sum of the resistances of one or more PTC elements (mathematically expressed as ∑R < ∑R), PTC ()( Figure 5D However, when the heater temperature is much lower than the temperature limit condition, one or more PTC elements will begin to generate more power than one or more resistive elements. Therefore, the heater power output limiting characteristic will be slower.

[0051] The ratio of the sum of the two resistances (∑R / ∑R) PTC The larger the value of ∑R / ∑R, the flatter the power dissipation response over the temperature range. Furthermore, lower total power dissipation variation / instability will be caused by one or more PTC elements. Simultaneously, the peak power dissipated by one or more PTC elements will be lower, and vice versa. PTC The lower the ratio, the earlier the temperature limit occurs, and simultaneously, the higher the peak power of one or more PTC elements will be. Therefore, Figures 5A-5D The curves show a mechanism for adjusting heater characteristics as needed.

[0052] Figure 6A top view and a cross-sectional view of a resistive heating device or self-limiting heater 600 according to an exemplary embodiment are shown. Resistive elements or chip resistors 602a and 602b (collectively referred to as “resistors 602”) are shown disposed on a copper layer 606, with a PTC element 604 disposed therebetween. When a voltage is applied and current flows through resistors 602 and PTC element 604, heat is dissipated to aluminum layer 608. In the exemplary embodiment, there is good thermal coupling between resistors 602 and PTC element 604. Furthermore, in the exemplary embodiment, resistor 602 has a very small resistance change with temperature. The two resistors 502a and 502b may have similar, but are not required, temperature coefficients. Instead, in the exemplary embodiment, having two resistors on opposite sides of the PTC improves thermal coupling, such that approximately half of the heat comes from one side (resistor 502a) and the other half comes from the other side (resistor 502b). Furthermore, in an exemplary embodiment, the PTC 504 has a high temperature-dependent resistance and a positive temperature coefficient.

[0053] In an exemplary embodiment, the resistor has a first ohm resistance and the PTC has a second ohm resistance, with the first ohm resistance being far from the limiting condition. In one embodiment, the first ohm resistance is higher than the second ohm resistance. In a second embodiment, the first ohm resistance is similar to the second ohm resistance. In a third embodiment, the first ohm resistance is lower than the second ohm resistance. Therefore, the resistance ratio between the resistor and the PTC can be used to adjust the heater characteristics and limit the sharpness of the characteristics.

[0054] Figure 7 This includes a graph 700 showing test results for a self-limiting heater according to an exemplary embodiment. The graph depicts the relationship between temperature (°C) and total resistance (ohms), where total resistance is the resistance (R) of the resistive element. Resistor ) and the resistance (R) of the PTC element PTC The sum of the resistance values ​​is 0.08 ohms to 0.10 ohms. The heater operates within the range of 20°C to 120°C (LTR, or low-temperature resistance range), with only a slight change in resistance (between 0.08 ohms and 0.10 ohms). Once the temperature rises above 120°C, the resistance begins to increase significantly. Therefore, as designed, the heater is self-limiting. The solid line indicates the resistance of the PTC alone versus temperature, while the dashed line indicates the resistance of the PTC together with the resistor versus temperature. Therefore, the presence of both the PTC and the resistor ensures that the resistance becomes increasingly flat (approximately level) as the temperature increases.

[0055] The self-limiting heater 600 can be divided into smaller sections / units, each exhibiting similar performance. Alternatively, the metal-based substrate PCB in which the self-limiting heater 600 is formed can be combined in parallel with other heaters to form a larger heater for a suitable application.

[0056] In an exemplary embodiment, the self-limiting heater disclosed herein is designed to have good thermal coupling between one or more resistive elements and one or more PTC elements. This differs from a PTC fuse because limiting is triggered by the temperature of the rest of the circuit rather than by an increase in current.

[0057] Therefore, a self-limiting heater is disclosed, which has the ability to limit its heating power output. The self-limiting heater can effectively cut off power, or reduce power to a predefined limit. Many applications carry the risk of overheating. In conventional applications, temperature monitoring devices are part of the implementation to mitigate this risk. Such temperature monitoring can, for example, employ switching mechanisms such as relays, transistors, or switches to cut off the heater power supply. Another mechanism for controlling the risk of overheating is the use of power pulses.

[0058] The self-regulating heater disclosed herein avoids these additional protective measures. This is because once the heater reaches a certain predefined temperature, it automatically reduces its output power due to the aforementioned principles of the resistive and PTC elements. Furthermore, because it eliminates the need for additional monitoring circuitry, the self-limiting heater is protected from potential malfunctions that might occur in such circuits.

[0059] There are many risks of overheating in automotive applications. For example, a radiator, if it empties, can melt, causing it to deform, which can lead to loss of seal, perforation, or other problems. Urea tanks, used to protect against hazardous pollutants, can begin to decompose if heated. This happens rapidly at temperatures above 60°C, causing the urea tank to fail in its emission reduction function. Camera lenses are external parts of the vehicle, and if they overheat, they can cause burns when touched. Overheated batteries can catch fire or even explode. This can also happen in fuel / diesel lines. All these components, and many more, of a car can benefit from self-regulating heaters. Self-regulating features allow for the construction of smaller, high-power heaters because they offer greater stability and reduce these risks.

[0060] As used herein, elements or steps described in the singular and beginning with the words “a” or “an” should be understood to not exclude multiple elements or steps unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” in this disclosure are not intended to exclude the existence of appended embodiments that also include the referenced features.

[0061] While this disclosure references certain embodiments, various modifications, alterations, and variations of the embodiments are possible without departing from the scope and theme of this disclosure as defined in the appended claims. Therefore, it is intended that this disclosure is not limited to the described embodiments, but rather has the full scope defined by the language of the appended claims and their equivalents.

Claims

1. A self-limiting heater, comprising: Voltage source; A resistor, the resistor comprising a minimum resistance change with temperature; as well as Positive temperature coefficient PTC resistor, wherein the resistor and the PTC resistor are: They are electrically coupled in series with each other; They are thermally coupled to each other; and It is disposed on a metal-based printed circuit board (PCB), the metal-based PCB comprising: A substrate layer composed of a metal substrate, wherein the metal substrate is an aluminum-based alloy; A dielectric layer for absorbing heat when current flows through the resistor and the PTC resistor, wherein the heat is transferred to the base layer; and Circuit layers including copper foil; In response to the temperature rising to a temperature limit condition, the self-limiting heater automatically reduces its power output.

2. The self-limiting heater according to claim 1, wherein the resistor and the PTC resistor are chip resistors soldered onto the metal-based substrate PCB.

3. The self-limiting heater according to claim 1, wherein the resistor and the PTC resistor are screen-printed on the metal-based PCB.

4. The self-limiting heater of claim 1, wherein the resistor and the PTC resistor are applied to the metal-based substrate PCB using resistive ink.

5. The self-limiting heater of claim 2, wherein the resistor and the PTC resistor are soldered to the metal-based substrate PCB.

6. The self-limiting heater of claim 1, wherein the resistor has a first ohmic resistance, the PTC resistor has a second ohmic resistance, and the first ohmic resistance is located away from the temperature limiting condition.

7. The self-limiting heater according to claim 6, wherein the first ohmic resistor: It is higher than the second ohmic resistance.

8. The self-limiting heater according to claim 6, wherein the first ohmic resistor: Similar to the second ohmic resistor.

9. The self-limiting heater according to claim 6, wherein the first ohmic resistor: It is lower than the second ohmic resistance.

10. A method for manufacturing a self-limiting heater, the method comprising: A resistive element is coupled to a metal-based printed circuit board (PCB), the metal-based PCB comprising: A substrate layer composed of a metal substrate, wherein the metal substrate is an aluminum-based alloy; Dielectric layer; and Circuit layers including copper foil; and The positive temperature coefficient (PTC) element is coupled to the metal-based PCB substrate. The resistive element and the PTC element are connected in series and electrically coupled to each other; The resistive element and the PTC element are thermally coupled to each other; The dielectric layer absorbs heat when current flows through the resistive element and the PTC element, and the heat is transferred to the substrate layer and voltage is generated from the power source. The self-limiting heater automatically reduces its power output in response to the temperature rising to a temperature limit condition.

11. The method of claim 10, wherein the resistive element is a chip resistor.

12. The method of claim 11, wherein the PTC element is a second chip resistor.

13. The method of claim 12, further comprising soldering the chip resistor and the second chip resistor to the metal-based substrate PCB.

14. The method of claim 10, wherein the resistive element and the PTC element are screen-printed on the metal-based PCB.

15. The method of claim 13, further comprising coupling the resistive element and the PTC element to the metal-based substrate PCB.

16. The method of claim 10, wherein the resistive element and the PTC element are applied to the metal-based PCB using resistive ink.

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