Providing a completely electrically isolated fuse module

Abstract

A fuse module that provides full electrical isolation. The fuse module electrically connected between a first terminal and a second terminal can include a primary fuse element, a PPTC fuse connected in parallel with the primary fuse element, and a secondary fuse element connected in series with the PPTC fuse. During normal operating conditions, current can flow through the primary fuse element. During an overcurrent condition, the primary fuse element can open, and current can flow through the PPTC fuse. When the PPTC fuse reaches a predetermined temperature, heat from the PPTC fuse can melt the secondary fuse element, causing the secondary fuse element to open and providing full electrical isolation between the first terminal and the second terminal. In some embodiments, the predetermined temperature of the PPTC fuse at which the secondary fuse opens can be the trip temperature of the PPTC fuse.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application Serial No. 63 / 800,561, entitled “FUSE MODULE WITH A PYRO FUSE AND A THERMALLY PROTECTEDPPTC FUSE ELEMENT PROVIDING COMPLETE GALVANIC SEPARATION”, filed May 6, 2025, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure generally relates to circuit protection devices. More specifically, this disclosure relates to fuse modules including pyrotechnic fuses and polymeric positive temperature coefficient (PPTC) fuses that provide complete electrical isolation and thermal protection. Background Technology

[0004] Fuses are commonly implemented in electrical systems to provide overcurrent protection. For example, some fuse modules include fuses that can trip passively or actively. Some fuse modules also provide multiple paths for current flow. However, achieving complete galvanic separation remains challenging among known fuse modules.

[0005] Given the above situation, there is a continuous and ongoing need for improved fuse modules. Summary of the Invention

[0006] This brief overview is provided to present the selection of concepts in a simplified form, which will be further described in the detailed description below. This brief overview is not intended to identify key or essential features of the claimed subject matter, or to serve as an aid in determining the scope of the claimed subject matter.

[0007] In some embodiments, the fuse module may include a main fuse element, a PPTC fuse connected in parallel with the main fuse element, and a secondary fuse element connected in series with the PPTC fuse element, wherein current can flow through the main fuse element during normal operation, wherein during an overcurrent condition, the main fuse element can disconnect and current can flow through the PPTC fuse until the PPTC fuse reaches its tripping temperature, and wherein when the PPTC fuse reaches its tripping temperature, the secondary fuse element can disconnect.

[0008] In some embodiments, the main fuse element may include a pyrotechnic fuse.

[0009] In some embodiments, the secondary fuse element may include a thermal fuse.

[0010] In some embodiments, during an overcurrent condition, current can be diverted from the main fuse element to the PPTC fuse.

[0011] In some embodiments, the current flowing through the PPTC fuse can increase the operating temperature of the PPTC fuse. As the operating temperature of the PPTC fuse rises below the trip temperature, the resistance of the PPTC fuse can increase linearly, and when the operating temperature of the PPTC fuse reaches the trip temperature, the resistance of the PPTC fuse can increase non-linearly.

[0012] In some embodiments, when the operating temperature of the PPTC fuse reaches the tripping temperature, the resistance of the PPTC fuse can limit the current flowing through it.

[0013] In some embodiments, the current flowing through the PPTC fuse can increase the operating temperature of the PPTC fuse, and when the operating temperature of the PPTC fuse reaches the tripping temperature, the heat from the PPTC fuse can melt the heat-sensitive element in the secondary fuse element.

[0014] In some embodiments, the fuse module may include a first terminal electrically coupled to a primary fuse element and a PPTC fuse, and a second terminal electrically coupled to a primary fuse element and a secondary fuse element, wherein disconnection of the secondary fuse element can provide complete electrical isolation between the first and second terminals.

[0015] In some embodiments, the fuse module may include a main fuse element, a PPTC fuse connected in parallel with the main fuse element, and a secondary fuse element connected in series with the PPTC fuse element, wherein current can flow through the main fuse element during normal operation, wherein the main fuse element can disconnect and current can flow through the PPTC fuse element during overcurrent conditions, and wherein the secondary fuse element can disconnect when the PPTC fuse element reaches a predetermined temperature.

[0016] In some embodiments, during an overcurrent condition, current can be diverted from the main fuse element to the PPTC fuse.

[0017] In some embodiments, the current flowing through the PPTC fuse can increase the operating temperature of the PPTC fuse. As the operating temperature of the PPTC fuse rises below the trip temperature, the resistance of the PPTC fuse can increase linearly, and when the operating temperature of the PPTC fuse reaches the trip temperature, the resistance of the PPTC fuse can increase non-linearly.

[0018] In some embodiments, when the operating temperature of the PPTC fuse reaches the tripping temperature, the resistance of the PPTC fuse can limit the current flowing through it.

[0019] In some embodiments, the current flowing through the PPTC fuse can increase the operating temperature of the PPTC fuse, and when the operating temperature of the PPTC fuse reaches a predetermined temperature, the heat from the PPTC fuse can melt the heat-sensitive element in the secondary fuse element.

[0020] In some embodiments, the fuse module may include a first terminal electrically coupled to a main fuse element and a PPTC fuse, and a second terminal electrically coupled to a main fuse element and a secondary fuse element, wherein disconnection of the secondary fuse element can provide complete electrical isolation between the first terminal and the second terminal.

[0021] In some embodiments, the method may include: during normal operation, allowing current to flow through a main fuse element between a first terminal and a second terminal; during an overcurrent condition, disconnecting the main fuse element; during an overcurrent condition, allowing current to flow through a PPTC fuse connected in parallel with the main fuse element between the first terminal and the second terminal; and when the PPTC fuse reaches a predetermined temperature, disconnecting a secondary fuse element connected in series with the PPTC fuse to provide complete electrical isolation between the first terminal and the second terminal.

[0022] In some embodiments, the method may include diverting current from the main fuse element to the PPTC fuse during an overcurrent condition.

[0023] In some embodiments, the method may include: increasing the operating temperature of the PPTC fuse as current flows through it; linearly increasing the resistance of the PPTC fuse as the operating temperature of the PPTC fuse increases below the tripping temperature; and non-linearly increasing the resistance of the PPTC fuse when the operating temperature of the PPTC fuse reaches the tripping temperature.

[0024] In some embodiments, the method may include limiting the current flowing through the PPTC fuse when the operating temperature of the PPTC fuse reaches the tripping temperature.

[0025] In some embodiments, the method may include: melting a heat-sensitive element in a secondary fuse element with heat from the PPTC fuse when the operating temperature of the PPTC fuse reaches a predetermined temperature, wherein the predetermined temperature is a tripping temperature.

[0026] In some embodiments, the method may include: raising the operating temperature of the PPTC fuse as current flows through it; and melting a heat-sensitive element in a secondary fuse element with the heat from the PPTC fuse when the operating temperature of the PPTC fuse reaches a predetermined temperature.

[0027] Other technical features will be apparent to those skilled in the art from the following figures, description and claims. Attached Figure Description

[0028] To facilitate identification of any particular element or behavior being discussed, one or more of the most significant digits in the reference number refer to the figure number in which the element is first introduced.

[0029] Figure 1 This is a schematic diagram illustrating a pyrotechnic fuse according to a disclosed embodiment.

[0030] Figure 2 This is a schematic diagram illustrating a PPTC fuse and a thermal fuse according to the disclosed embodiments.

[0031] Figure 3A This is a circuit diagram illustrating the current flow in a fuse module according to the disclosed embodiment.

[0032] Figure 3B This is a circuit diagram illustrating the current flow in a fuse module according to the disclosed embodiment.

[0033] Figure 3C This is a circuit diagram illustrating complete electrical isolation in a fuse module according to the disclosed embodiments.

[0034] Figure 4 This is a flowchart illustrating a method according to the disclosed embodiments. Detailed Implementation

[0035] Exemplary embodiments of fuse modules that can provide full electrical isolation according to this disclosure will now be described more fully below with reference to the accompanying drawings. However, fuse modules can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will convey certain exemplary aspects of fuse modules to those skilled in the art.

[0036] According to the disclosed embodiments, the fuse module can be connected between the first terminal and the second terminal. The fuse module may include a main fuse element connected in parallel with the PPTC fuse and a secondary fuse element connected in series with the PPTC fuse.

[0037] During normal operation, current can flow through the main fuse element. However, in the event of an overcurrent condition, the main fuse element may trip, generating an arc voltage across it. With the presence of this arc voltage, current can be diverted to the PPTC fuse. However, as current flows through the PPTC fuse, its operating temperature may rise. When the PPTC fuse reaches a predetermined operating temperature, the heat from the fuse can cause the secondary fuse element to trip, thus creating complete electrical isolation between the first and second terminals.

[0038] In some embodiments, when the operating temperature of the PPTC fuse reaches the trip temperature, the PPTC fuse can enter a tripped state. For example, in the tripped state, the resistance of the PPTC fuse can increase sharply, resulting in a sharp decrease in the current flowing through the PPTC fuse. When the PPTC fuse is in the tripped state, it can limit the current flowing through it. In some embodiments, the predetermined temperature of the PPTC fuse can be the trip temperature. That is, in some embodiments, when the operating temperature of the PPTC fuse reaches the trip temperature, the heat from the PPTC fuse can cause the secondary fuse element to disconnect.

[0039] As disclosed herein, a fuse module may include a main fuse element, a PPTC fuse connected in parallel with the main fuse element, and a secondary fuse element connected in series with the PPTC fuse. In some embodiments, the main fuse element may include a pyro fuse or a portion thereof.

[0040] For example, Figure 1 This is a schematic diagram illustrating a pyrotechnic fuse 100 according to a disclosed embodiment. It is to be understood that the pyrotechnic fuse 100 is merely exemplary, and additional or alternative main fuse elements and / or pyrotechnic fuses are contemplated. For example, in some embodiments, the main fuse element may include a fuse module shown and described in U.S. Patent No. 11,387,068, which is incorporated herein by reference.

[0041] As in Figure 1As seen in the diagram, the pyrotechnic fuse 100 may include a housing 102 having a shaft 112 formed therein. A busbar 104 may be disposed within the housing 102 and extend through the housing 102 to the outside of the housing 102, and the busbar 104 may include a fuse element 106 electrically connected to the busbar 104, such that it is at least partially disposed within the shaft 112. A movable piston 108 and an initiator 110 may also be disposed within the shaft 112, wherein the piston 108 is disposed above the fuse element 106, and the initiator 110 is disposed above the piston 108. The initiator 110 may also be coupled to a controller (not shown).

[0042] During operation, current can flow from lead 114 or terminal to busbar 104, through busbar 104 (including fuse element 106), and from busbar 104 to lead 116 or terminal. However, the current can be interrupted in response to the occurrence of a predetermined event. Specifically, upon the occurrence of a predetermined event, the controller can send a start signal to trigger 110, causing trigger 110 to detonate. The resulting increase in pressure within shaft 112 can rapidly force piston 108 downward within shaft 112 and through fuse element 106 to cut off fuse element 106, thereby separating fuse element 106 from busbar 104 and interrupting the current flowing through busbar 104. Figure 1 The piston 108 is shown after the fuse element 106 is cut off (where the fuse element 106 is separated from the bus bar 104).

[0043] As disclosed herein, a fuse module may include a main fuse element, a PPTC fuse connected in parallel with the main fuse element, and a secondary fuse element connected in series with the PPTC fuse. In some embodiments, the secondary fuse element may include a thermal fuse or a portion thereof.

[0044] For example, Figure 2 This is a schematic diagram illustrating a PPTC fuse 202 and a thermal fuse 204 according to the disclosed embodiments. It is to be understood that the PPTC fuse 202 and the thermal fuse 204 are merely exemplary, and additional or alternative PPTC fuses and / or thermal fuses are contemplated, including their relative orientation, size, shape, and position relative to each other.

[0045] As in Figure 2As seen in the diagram, the PPTC fuse 202 can be circular, oval, or otherwise shaped to surround and electrically contact a conductor (such as conductive layer 208). That is, the conductive layer 208 can be at least partially surrounded by the PPTC fuse 202. Furthermore, an insulator (such as insulating layer 206) can be disposed on one side of the conductive layer 208 to provide electrical insulation, for example, by covering at least a portion of the conductive layer 208. A thermal fuse 204 can be disposed on the side of the conductive layer 208 having the insulating layer 206, such that a first end of the thermal fuse 204 is coupled to and electrically contacts the conductive layer 208, and a second end of the thermal fuse 204 is coupled to the insulating layer 206.

[0046] During operation, current can flow from lead 210 or terminal to PPTC fuse 202, through PPTC fuse 202, from PPTC fuse 202 to conductive layer 208, from conductive layer 208 to thermal fuse 204, through thermal fuse 204, and from thermal fuse 204 to lead 210 or terminal. However, the current can be interrupted in response to a temperature rise that causes an increase in resistance of PPTC fuse 202 and / or thermal fuse 204 to melt, disintegrate, or otherwise disconnect.

[0047] Figure 3A , Figure 3B and Figure 3C This is a circuit diagram illustrating the current flow in a fuse module according to a disclosed embodiment. Figure 3A , Figure 3B and Figure 3C As seen and disclosed herein, PPTC fuse 304 may be connected in parallel with primary fuse element 302, and secondary fuse element 306 may be connected in series with PPTC fuse 304. For example, in some embodiments, primary fuse element 302 may be the same as or similar to pyrotechnic fuse 100. Additionally or alternatively, in some embodiments, PPTC fuse 304 may be the same as or similar to PPTC fuse 202, and secondary fuse element 306 may be the same as or similar to thermal fuse 204.

[0048] As in Figure 3A , Figure 3B and Figure 3C As also seen, the first terminal 310 can be electrically coupled to the main fuse element 302 and the PPTC fuse 304, and the second terminal 312 can be electrically coupled to the main fuse element 302 and the secondary fuse element 306. Therefore, the fuse module may include the main fuse element 302, the PPTC fuse 304, and the secondary fuse element 306 coupled between the first terminal 310 and the second terminal 312.

[0049] Figure 3A The current flow in the fuse module during normal operating conditions is shown. (As in...) Figure 3A As seen in the diagram, during normal operation, current 308 can flow through the main fuse element 302. Specifically, current 308 can flow from the first terminal 310 to the main fuse element 302, through the main fuse element 302, and from the main fuse element 302 to the second terminal 312. In some embodiments, during normal operation, current 308 does not flow through the PPTC fuse 304 or the secondary fuse element 306.

[0050] Figure 3B The current flow in the fuse module during an overcurrent condition is shown. (As in...) Figure 3B As seen in the diagram, during an overcurrent condition, the primary fuse element 302 can disconnect. For example, in some embodiments, the piston 108 can cut off fuse element 106 to interrupt current flow. In any embodiment, when the primary fuse element 302 disconnects during an overcurrent condition, current 308 can flow through the PPTC fuse 304 and the secondary fuse element 306. Specifically, current 308 can flow from the first terminal 310 to the PPTC fuse 304, through the PPTC fuse 304, from the PPTC fuse 304 to the secondary fuse element 306, through the secondary fuse element 306, and from the secondary fuse element 306 to the second terminal 312. Therefore, in some embodiments, current 308 can be diverted from the primary fuse element 302 to the PPTC fuse 304 during an overcurrent condition so that it does not flow through the primary fuse element 302 during an overcurrent condition.

[0051] When current 308 flows through PPTC fuse 304 and secondary fuse element 306, current 308 can flow from the first terminal 310 to the second terminal 312. In this respect, during overcurrent conditions, when the operating temperature of PPTC fuse 304 is below the tripping temperature, current 308 can flow freely through PPTC fuse 304.

[0052] However, the current 308 flowing through the PPTC fuse 304—both before and after the PPTC fuse 304 reaches its trip temperature—can cause the operating temperature of the PPTC fuse 304 to rise. As the operating temperature of the PPTC fuse 304 is below the trip temperature, its resistance can increase linearly, but when the operating temperature of the PPTC fuse 304 is at or above the trip temperature, its resistance can increase non-linearly. Therefore, at the trip temperature, the resistance of the PPTC fuse 304 can be high enough to limit the current 308 flowing through it.

[0053] However, even when the PPTC fuse 304 limits the current 308 flowing through it, a small amount of current 308 may still continue to flow from the first terminal 310 through the PPTC fuse 304 and the secondary fuse element 306 to the second terminal 312. Therefore, electrical isolation is not achieved.

[0054] Advantageously, when the operating temperature of the PPTC fuse 304 reaches a predetermined temperature, the heat from the PPTC fuse 304 can melt the heat-sensitive element in the secondary fuse element 306. That is, when the PPTC fuse 304 reaches the predetermined temperature, the secondary fuse element 306 can be disconnected, thereby providing complete electrical isolation between the first terminal 310 and the second terminal 312.

[0055] Figure 3C The current flow in the fuse module during this complete electrical isolation is shown. (As in...) Figure 3C As seen in the diagram, the secondary fuse element 306 is disconnected. For example, in some embodiments, the thermal fuse 204 may melt, disintegrate, or otherwise disconnect in response to heat from the PPTC fuse 304. In any embodiment, when the secondary fuse element 306 is disconnected, current 308 may flow through the PPTC fuse 304, but current 308 cannot flow through the secondary fuse element 306. Specifically, current 308 may flow from the first terminal 310 to the PPTC fuse 304, through the PPTC fuse 304, and from the PPTC fuse 304 to the secondary fuse element 306, but cannot flow through the secondary fuse element 306, and therefore cannot reach the second terminal 312, thereby providing complete electrical isolation between the first terminal 310 and the second terminal 312.

[0056] In some embodiments, the predetermined temperature at which the heat from the PPTC fuse 304 melts the heat-sensitive element in the secondary fuse element 306 can be the tripping temperature of the PPTC fuse 304. Therefore, when the operating temperature of the PPTC fuse 304 reaches the tripping temperature, the heat from the PPTC fuse 304 can melt the heat-sensitive element in the secondary fuse element 306. That is, when the PPTC fuse 304 reaches the tripping temperature, the secondary fuse element 306 can disconnect.

[0057] Figure 4 This is a flowchart illustrating a method 400 according to a disclosed embodiment. In some embodiments, by Figure 3A , Figure 3B and Figure 3C The circuit diagram shows that the fuse module can perform some or all of method 400.

[0058] As can be seen, method 400 may include, as in 402, allowing current to flow through a main fuse element between the first and second terminals during normal operating conditions. For example, in some embodiments, current may flow through a pyrotechnic fuse 100.

[0059] Method 400 may further include, as in 404, disconnecting the main fuse element during an overcurrent condition, and as in 406, allowing current to flow through a PPTC fuse connected in parallel with the main fuse element between the first and second terminals during an overcurrent condition. For example, in some embodiments, method 400 may include diverting current from the main fuse element to the PPTC fuse during an overcurrent condition.

[0060] Finally, method 400 may include, as in 408, disconnecting the secondary fuse element connected in series with the PPTC fuse when the PPTC fuse reaches a predetermined temperature, thereby providing complete electrical isolation between the first and second terminals. For example, in some embodiments, method 400 may include increasing the operating temperature of the PPTC fuse as current flows through it, and melting the heat-sensitive element in the secondary fuse element with the heat from the PPTC fuse when the operating temperature of the PPTC fuse reaches the predetermined temperature.

[0061] In some embodiments, method 400 may further include: linearly increasing the resistance of the PPTC fuse as the operating temperature of the PPTC fuse increases below the trip temperature, and non-linearly increasing the resistance of the PPTC fuse when the operating temperature of the PPTC fuse reaches the trip temperature. In these embodiments, method 400 may include: limiting the current flowing through the PPTC fuse when the operating temperature of the PPTC fuse reaches the trip temperature.

[0062] In some embodiments, the predetermined temperature may be the trip temperature. In particular, in some embodiments, method 400 may include: melting the heat-sensitive element in the secondary fuse element with heat from the PPTC fuse when the operating temperature of the PPTC fuse reaches the trip temperature.

[0063] As used herein, elements or steps described in the singular and referred to by 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 be construed as excluding the existence of additional embodiments that also include the described features.

[0064] While this disclosure references certain embodiments, numerous modifications, alterations, and variations of the described embodiments are possible without departing from the spirit and scope of this disclosure as defined in the appended claims. Therefore, this disclosure is intended to be limited to the described embodiments, but rather to have the full scope defined by the language of the following claims and their equivalents.

Claims

1. A fuse module, comprising: Main fuse element; A PPTC fuse connected in parallel with the main fuse element; as well as The secondary fuse element connected in series with the PPTC fuse, During normal operation, current flows through the main fuse element. During an overcurrent condition, the main fuse element disconnects and the current flows through the PPTC fuse until the PPTC fuse reaches its tripping temperature. Specifically, when the PPTC fuse reaches the tripping temperature, the secondary fuse element disconnects.

2. The fuse module according to claim 1, wherein, The main fuse element includes a pyrotechnic fuse.

3. The fuse module according to claim 1, wherein, The secondary fuse element includes a thermal fuse.

4. The fuse module according to claim 1, wherein, During an overcurrent condition, the current is diverted from the main fuse element to the PPTC fuse.

5. The fuse module according to claim 1, wherein, The current flowing through the PPTC fuse increases the operating temperature of the PPTC fuse, wherein the resistance of the PPTC fuse increases linearly as the operating temperature of the PPTC fuse rises below the trip temperature, and wherein the resistance of the PPTC fuse increases non-linearly when the operating temperature of the PPTC fuse reaches the trip temperature.

6. The fuse module according to claim 5, wherein, When the operating temperature of the PPTC fuse reaches the tripping temperature, the resistance of the PPTC fuse limits the current flowing through it.

7. The fuse module according to claim 1, wherein, The current flowing through the PPTC fuse increases the operating temperature of the PPTC fuse, and when the operating temperature of the PPTC fuse reaches the tripping temperature, the heat from the PPTC fuse melts the heat-sensitive element in the secondary fuse element.

8. The fuse module according to claim 1, further comprising: The first terminal is electrically coupled to the main fuse element and the PPTC fuse; as well as The second terminal is electrically coupled to both the primary fuse element and the secondary fuse element. The disconnection of the secondary fuse element provides complete electrical isolation between the first terminal and the second terminal.

9. A fuse module, comprising: Main fuse element; A PPTC fuse connected in parallel with the main fuse element; as well as The secondary fuse element connected in series with the PPTC fuse, During normal operation, current flows through the main fuse element. During an overcurrent condition, the main fuse element breaks and the current flows through the PPTC fuse. When the PPTC fuse reaches a predetermined temperature, the secondary fuse disconnects.

10. The fuse module according to claim 9, wherein, During the overcurrent condition, the current is diverted from the main fuse element to the PPTC fuse.

11. The fuse module according to claim 9, wherein, The current flowing through the PPTC fuse increases the operating temperature of the PPTC fuse, wherein the resistance of the PPTC fuse increases linearly as the operating temperature of the PPTC fuse rises below the trip temperature, and wherein the resistance of the PPTC fuse increases non-linearly when the operating temperature of the PPTC fuse reaches the trip temperature.

12. The fuse module according to claim 11, wherein, When the operating temperature of the PPTC fuse reaches the tripping temperature, the resistance of the PPTC fuse limits the current flowing through it.

13. The fuse module according to claim 9, wherein, The current flowing through the PPTC fuse increases the operating temperature of the PPTC fuse, and when the operating temperature of the PPTC fuse reaches the predetermined temperature, the heat from the PPTC fuse melts the heat-sensitive element in the secondary fuse element.

14. The fuse module according to claim 9, further comprising: The first terminal is electrically coupled to the main fuse element and the PPTC fuse; as well as The second terminal is electrically coupled to both the primary fuse element and the secondary fuse element. The disconnection of the secondary fuse element provides complete electrical isolation between the first terminal and the second terminal.

15. A method comprising: During normal operation, current flows through the main fuse element between the first and second terminals; During an overcurrent condition, the main fuse element is disconnected; During the overcurrent condition, the current is allowed to flow through the PPTC fuse connected in parallel with the main fuse element between the first terminal and the second terminal; and When the PPTC fuse reaches a predetermined temperature, the secondary fuse element connected in series with the PPTC fuse is disconnected to provide complete electrical isolation between the first terminal and the second terminal.

16. The method of claim 15, further comprising: During the overcurrent condition, the current is diverted from the main fuse element to the PPTC fuse.

17. The method of claim 15, further comprising: The operating temperature of the PPTC fuse increases as the current flows through it; As the operating temperature of the PPTC fuse increases below the tripping temperature, the resistance of the PPTC fuse increases linearly; and When the operating temperature of the PPTC fuse reaches the tripping temperature, the resistance of the PPTC fuse is increased in a non-linear manner.

18. The method of claim 17, further comprising: When the operating temperature of the PPTC fuse reaches the tripping temperature, the current flowing through the PPTC fuse is limited.

19. The method of claim 18, further comprising: When the operating temperature of the PPTC fuse reaches the predetermined temperature, the heat from the PPTC fuse melts the heat-sensitive element in the secondary fuse element. The predetermined temperature is the tripping temperature.

20. The method of claim 15, further comprising: The operating temperature of the PPTC fuse increases as the current flows through it; and When the operating temperature of the PPTC fuse reaches the predetermined temperature, the heat from the PPTC fuse melts the heat-sensitive element in the secondary fuse element.

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