Patent Publication Number: US-2023144937-A1

Title: Resettable electronic fuse for high-power devices

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/876,099 filed on Jul. 19, 2019, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Devices such as battery packs and battery pack chargers conventionally include a fuse in a charge or discharge current path to protect such devices from high or excessive currents. For example, a battery pack may include a fuse connected in series with one or more semiconductor switching devices (e.g., FETs). A high current could cause the fuse to be opened to protect the battery pack (e.g., the battery pack&#39;s cells) from the high current. 
     SUMMARY 
     Conventional fuses positioned in a charge or discharge path of a device for protecting the device from high or excessive currents have several drawbacks. The use of conventional fuses can render the device inoperable if the fuse were to be opened. For example, an opened fuse could render the device entirely inoperable or could at least require the device to be repaired and returned to working order. High-power application devices (e.g., devices outputting or receiving average currents of 20 amps or greater), such as power tools, battery packs for power tools, and battery pack chargers, frequently experience high currents that have the potential to open the fuse and render such devices inoperable. It would be advantageous in such high-power devices to remove and replace conventional fuses with a resettable electronic fuse. As a result, a fault or trip condition that causes the resettable electronic fuse to trip or open, does not permanently disable the device. Rather, the resettable electronic fuse or a controller connected to the resettable electronic fuse can be configured to reset the resettable electronic fuse to again make the device operable. Such a resettable electronic fuse can also be implemented in such a manner that it complies with the standards of one or more safety certification organizations, such as Underwriters Laboratories (“UL”). 
     A resettable electronic fuse can be implemented in devices to replace, for example, the combination of a conventional fuse and a single semiconductor switch (e.g., a FET), the combination of a conventional fuse and dual semiconductor switches (e.g., FETs), etc. The resettable electronic fuse can provide devices with a net savings in space (e.g., by having a smaller circuit footprint), cost (e.g., by replacing multiple components with a single component), and heat generation. For example, a conventional fuse, in addition to any series-connected semiconductor switches, all generate heat when passing current. By removing the conventional fuse and replacing it with a resettable electronic fuse, there are fewer devices in a current path to generate heat. Reduced heat dissipation by a device can also reduce heat sinking requirements for the device, which can further provide cost and space savings. 
     Embodiments described herein provide a resettable electronic fuse for a device (e.g., a high-power device), such as a power tool, a battery pack for the power tool, or a battery pack charger. The resettable electronic fuse is connected in a current path of the device and is operable or configured to selectively interrupt current passing through the resettable electronic fuse based on a detected condition of the device (e.g., a detected fault condition of the device). The resettable electronic fuse is also configured to be reset after a detected fault condition has ended. In some embodiments, the resettable electronic fuse is configured to reset itself. In other embodiments, the resettable electronic fuse is configured to receive a signal (e.g., from a device controller) to reset. 
     Embodiments described herein provide a device including a path for passing electric current. The device also includes a terminal and a resettable electronic fuse. The resettable electronic fuse is in the path for passing electric current and is electrically connected to the terminal. The resettable electronic fuse includes a semiconductor switch including a conductive state and a nonconductive state, a driver circuit configured to control the semiconductor switch into either the conductive state or the nonconductive state, a sensing circuit configured to sense a parameter of the device, and a comparing circuit configured to compare the parameter of the device to a first reference value for the parameter of the device. The driver circuit is configured to control the semiconductor switch into the nonconductive state when the parameter of the device is greater than or equal to the first reference value for the parameter of the device. 
     Embodiments described herein provide a device including a path for passing electric current. The device incudes a terminal and a resettable electronic fuse. The resettable electronic fuse is electrically connected to the terminal. The resettable electronic fuse includes a first semiconductor switch including a conductive state and a nonconductive state, a second semiconductor switch including a conductive state and a nonconductive state, a driver circuit, a sensing circuit, and a comparing circuit. The driver circuit is configured to control the first semiconductor switch into either the conductive state or the nonconductive state and to control the second semiconductor switch into either the conductive state or the nonconductive state. The sensing circuit is configured to sense a parameter of the device. The comparing circuit is configured to compare the parameter of the device to a reference value for the parameter. The driver circuit is configured to control at least one of the first semiconductor switch and the second semiconductor switch into the nonconductive state when the parameter of the device is greater than or equal to the reference value for the parameter. 
     Embodiments described herein provide a device including a path for passing electric current from a power source. The device includes a terminal connected to the power source in the path for passing electric current and a resettable electronic fuse. The resettable electronic fuse includes a semiconductor switch connected to the terminal and including a conductive state and a nonconductive state, a driver circuit configured to control the semiconductor switch into either the conductive state or the nonconductive state, a sensing circuit configured to sense the electric current from the power source, and a comparing circuit configured to compare the electric current to a first reference value. The driver circuit is configured to control the semiconductor switch into the nonconductive state when the electric current is greater than or equal to the first reference value. 
     Embodiments described herein provide a method of operating a resettable electronic fuse. The resettable electronic fuse includes a semiconductor switch. The method includes monitoring a parameter of a device, determining whether the monitored parameter of the device is indicative of a fault condition of the device, generating an interrupt signal when the monitored parameter of the device is indicative of the fault condition of the device, controlling the semiconductor switch into a nonconductive state based on the interrupt signal, generating a reset signal after the semiconductor switch is controlled into the nonconductive state, and controlling the semiconductor switch into a conductive state based on the reset signal. 
     Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in its application to the details of the configuration and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The embodiments are capable of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
     In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on non-transitory computer-readable medium) executable by one or more processing units, such as a microprocessor and/or application specific integrated circuits (“ASICs”). As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components, may be utilized to implement the embodiments. For example, “servers” and “computing devices” described in the specification can include one or more processing units, one or more computer-readable medium modules, one or more input/output interfaces, and various connections (e.g., a system bus) connecting the components. 
     Other aspects of the embodiments will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a battery pack that includes a resettable electronic fuse, according to embodiments described herein. 
         FIG.  2    illustrates a control system for the battery pack of  FIG.  1   , according to embodiments described herein. 
         FIG.  3    illustrates a device that includes a resettable electronic fuse, according to embodiments described herein. 
         FIG.  4    illustrates a control system for the device of  FIG.  3   , according to embodiments described herein. 
         FIG.  5    illustrates a battery pack charger that includes a resettable electronic fuse, according to embodiments described herein. 
         FIG.  6    illustrates a control system for the device of  FIG.  5   , according to embodiments described herein. 
         FIG.  7    illustrates a resettable electronic fuse, according to embodiments described herein. 
         FIG.  8    is a process for operating a resettable electronic fuse, according to embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein relate to one or more devices (e.g., high-power devices) that include a path for passing electric current. The devices include a resettable electronic fuse connected in the path for selectively controlling electric current on the path. For example, the one or more devices include a battery pack, a device such as a power tool, and a battery pack charger. The resettable electronic fuse includes one or more semiconductor switches, a driver circuit, a sensing or monitoring circuit, and a comparing circuit. The driver circuit is configured to selectively control a conductive state of the one or more semiconductor switches. The sensing or monitoring circuit is configured to sense or monitor a parameter of the device. The comparing circuit receives a signal from the sensing or monitoring circuit related to the parameter of the device and compares the signal to a reference signal. The comparing circuit generates an output signal for the driver circuit, and the drive circuit is configured to selectively control the conductive state of the one or more semiconductor switches based on the output signal from the comparing circuit. In some embodiments, the resettable electronic fuse is also configured to receive a signal from a controller of the device related to a second parameter of the device. The drive circuit is also configured to selectively control the conductive state of the one or more semiconductor switches based on the signal from the controller. 
     By controlling the conductive state of the one or more semiconductor switches, the driver circuit can trip or open the path for passing electric current to prevent current from passing. After the resettable electronic fuse has been tripped or opened, the resettable electronic fuse is also configured to be reset after, for example, a detected fault condition has ended. Although embodiments described herein can be applied to, performed by, or used in conjunction with a variety of high-power devices, embodiments described herein are described primarily with respect to a battery pack, a device such as a power tool, and a battery pack charger. 
       FIG.  1    illustrates a battery pack  100  that includes a resettable electronic fuse or e-fuse. The battery pack  100  includes a housing  105  and an interface portion  110  for connecting the battery pack  100  to a device (e.g., a power tool). The resettable electronic fuse is configured to, for example, disable current into the battery pack  100  or out of the battery pack  100  by opening a current charge/discharge path of the battery pack  100 . In some embodiments, the resettable electronic fuse is provided in a charge path or in a discharge path or in a path that both charges and discharges. The sizing and/or current thresholds of the resettable electronic fuse may vary depending on the particular path, such as smaller for a charge path and larger for a discharge path. In some embodiments, the resettable electronic fuse is a discrete component that includes one or more inputs and one or more outputs for passing current. For example, the resettable electronic fuse can be implemented as an integrated circuit including a casing or housing that encloses the resettable electronic fuse&#39;s circuitry. In other embodiments, the resettable electronic fuse does not include a casing or a housing and the resettable electronic fuse&#39;s circuitry is generally exposed. In some embodiments, the resettable electronic fuse is connected to a printed circuit board (“PCB”) as a singular unit. In other embodiments, a plurality of discrete components are individually connected to a PCB and connected such that the plurality of discrete components collectively form a resettable electronic fuse. In some embodiments, the battery pack  100  includes a plurality of resettable electronic fuses. 
     The resettable electronic fuse is independently resettable (i.e., the electronic fuse is operable to or capable of resetting itself) and/or the resettable electronic fuse can be reset by a separate, external component (e.g., a battery pack controller, a power tool, a battery pack charger, etc.). For example, the resettable electronic fuse can be electrically and/or communicatively connected to a controller of the battery pack  100  such that the resettable electronic fuse provides signals to the controller or receives signals from the controller. The controller of the battery pack  100  is configured to receive, for example, a signal from the resettable electronic fuse indicating that the resettable electronic fuse has tripped. The controller of the battery pack  100  is also configured to generate and transmit a signal to the resettable electronic fuse to reset the electronic fuse. In some embodiments, the controller of the battery pack  100  is also configured to generate and transmit a signal to the resettable electronic fuse to provide an alternative signal to trip or open the resettable electronic fuse. For example, the controller of the battery pack  100  can sense or monitor a parameter of the battery pack  100  (e.g., battery cell voltage, temperature, etc.) for a fault condition and, based on the sensed or monitored parameter, provide the alternative signal to the resettable electronic fuse that causes the resettable electronic fuse to trip or open. In some embodiments, the controller trips if either the resettable electronic fuse identifies a trip condition or the alternative trip signal is received. In some embodiments, the resettable electronic fuse is reset only when both controller of the battery pack  100  and the resettable electronic fuse determine that a fault condition is cleared (e.g., switches can again be closed). 
       FIG.  2    illustrates a control system for the battery pack  100 . The control system includes a controller  200 . The controller  200  is electrically and/or communicatively connected to a variety of modules or components of the battery pack  100 . For example, the illustrated controller  200  is connected to one or more battery cells  205  and an interface  210  (e.g., the interface portion  110  of the battery pack  100  illustrated in  FIG.  1   ). The controller  200  is also connected to one or more voltage sensors or voltage sensing circuits  215 , one or more current sensors or current sensing circuits  220 , and one or more temperature sensors or temperature sensing circuits  225 . A resettable electronic fuse  230  is connected between the one or more battery cells  205  and the interface  210 . The controller  200  includes combinations of hardware and software that are operable to, among other things, control the operation of the battery pack  100 , control the operation of the resettable electronic fuse  230 , monitor a condition of the battery pack  100 , enable or disable charging of the battery pack  100 , enable or disable discharging of the battery pack  100 , etc. 
     The controller  200  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  200  and/or the battery pack  100 . For example, the controller  200  includes, among other things, a processing unit  235  (e.g., a microprocessor, a microcontroller, or another suitable programmable device), a memory  240 , input units  245 , and output units  250 . The processing unit  235  includes, among other things, a control unit  255 , an arithmetic logic unit (“ALU”)  260 , and a plurality of registers  265  (shown as a group of registers in  FIG.  2   ), and is implemented using a known computer architecture (e.g., a modified Harvard architecture, a von Neumann architecture, etc.). The processing unit  235 , the memory  240 , the input units  245 , and the output units  250 , as well as the various modules or circuits connected to the controller  200  are connected by one or more control and/or data buses (e.g., common bus  270 ). The control and/or data buses are shown generally in  FIG.  2    for illustrative purposes. The use of one or more control and/or data buses for the interconnection between and communication among the various modules, circuits, and components would be known to a person skilled in the art in view of the invention described herein. 
     The memory  240  is a non-transitory computer readable medium and includes, for example, a program storage area and a data storage area. The program storage area and the data storage area can include combinations of different types of memory, such as a ROM, a RAM (e.g., DRAM, SDRAM, etc.), EEPROM, flash memory, a hard disk, an SD card, or other suitable magnetic, optical, physical, or electronic memory devices. The processing unit  235  is connected to the memory  240  and executes software instructions that are capable of being stored in a RAM of the memory  240  (e.g., during execution), a ROM of the memory  240  (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or a disc. Software included in the implementation of the battery pack  100  can be stored in the memory  240  of the controller  200 . The software includes, for example, firmware, one or more applications, program data, filters, rules, one or more program modules, and other executable instructions. The controller  200  is configured to retrieve from the memory  240  and execute, among other things, instructions related to the control processes and methods described herein. In other constructions, the controller  200  includes additional, fewer, or different components. 
     The interface  210  includes a combination of mechanical components (e.g., rails, grooves, latches, etc.) and electrical components (e.g., one or more terminals) configured to and operable for interfacing (e.g., mechanically, electrically, and communicatively connecting) the battery pack  100  with another device (e.g., a power tool, a battery pack charger, etc.). For example, the interface  210  is configured to receive power through the resettable electronic fuse  230  via a power line  275  between the one or more battery cells  205  and the interface  210 . The interface  210  is also configured to communicatively connect to the controller  200  via a communications line  280 . In some embodiments, the controller  200  is also electrically and/or communicatively connected to the resettable electronic fuse  230  via a signal line  285 . 
     The controller  200  is configured to determine whether a fault condition of the battery pack  100  is present and generate one or more control signals related to the fault condition. For example, the controller  200  is configured to detect an overvoltage condition of the one or more battery cells  205 , and under voltage condition of the one or more battery cells  205 , an over current condition (e.g., during charging or discharging), or an over temperature condition (e.g., during charging or discharging). In some embodiments, the over current condition corresponds to a particular current that is sensed for a particular amount of time. In some embodiments, an over current condition is detected when a current of between approximately 3 Amperes and 20 Amperes is detected for a predetermined amount of time (e.g., between 100 nano-seconds and 50 milli-seconds, or between 100 milli-seconds and 2 seconds). The amount of time and the detected current can be varied for different applications. In some embodiments, a current of between 3 Amperes and 20A Amperes can be detected for up to 50 milli-seconds before a fault condition occurs. In other embodiments, a current of between 3 Amperes and 20A Amperes can be detected for between 50 milli-seconds and several minutes (e.g., between 1 minute and 20 minutes) before a fault condition occurs. In some embodiments, a current of greater than 20 Amperes can be detected for between 50 milli-seconds and several minutes (e.g., between 1 minute and 20 minutes) before a fault condition occurs. In some embodiments, a current of approximately 30 Amperes can be detected for approximately 50 milli-seconds before a fault condition occurs. In some embodiments, a current of approximately 70 Amperes can be detected for approximately 100 nano-seconds before a fault condition occurs. In some embodiments, the current and trip times depend on the path in which the resettable electronic fuse is placed. For example, in a charging path, a trip current of approximately 3 Amperes to 20 Amperes can be detected for approximately 100 milli-seconds up to 2 seconds before a fault occurs. In a discharging path, a trip current of approximately 20 Amperes to 150 Amperes can be detected for approximately 500 milli-seconds up to 2 seconds before a fault occurs. 
     In some embodiments, the current threshold, the time threshold, or both the current threshold and the trip threshold are adjusted based upon which device is connected to the device with the resettable electronic fuse. For example, if the resettable electronic fuse is in a charger, the charger could raise or lower the trip threshold depending on the charging capability of the battery pack connected to it. 
     If the controller  200  detects one or more fault conditions of the battery pack  100  or determines that a fault condition of the battery pack no longer exists, the controller  200  is configured to provide information and/or control signals to another component of the battery pack  100  (e.g. the interface  210 , the resettable electronic fuse  230 , etc.). The signals can be configured to, for example, trip or open the resettable electronic fuse  230 , reset the resettable electronic fuse  230 , etc. In some embodiments, the resettable electronic fuse  230  is configured to independently sense or monitor a parameter of the battery pack  100  and independently trip or open based on the sensed or monitored parameter. 
       FIG.  3    illustrates a device  300  that includes a resettable electronic fuse or e-fuse. In the embodiment illustrated in  FIG.  3   , the device is a power tool (e.g., a drill/driver). In other embodiments, the device  300  is a different type of power tool (e.g., an impact wrench, a ratchet, a saw, a hammer drill, an impact driver, a rotary hammer, a grinder, a blower, a trimmer, etc.) or a different type of device (e.g., a light, a non-motorized sensing tool, etc.). The device  300  includes a housing  305  and an interface portion  310  for connecting the device  300  to, for example, the battery pack  100  or another device. The resettable electronic fuse is configured to, for example, disable current into the device  300  by opening a current path of the device  300 . As described above with respect to the battery pack  100 , in some embodiments, the resettable electronic fuse is a discrete component that includes a casing or housing and one or more inputs and one or more outputs for passing current. In other embodiments, the resettable electronic fuse does not include a casing or a housing and the resettable electronic fuse&#39;s circuitry is generally exposed. In some embodiments, the resettable electronic fuse is connected to a PCB as a singular unit. In other embodiments, a plurality of discrete components are individually connected to a PCB and connected such that the plurality of discrete components collectively form a resettable electronic fuse. In some embodiments, the device  300  includes a plurality of resettable electronic fuses. 
     The resettable electronic fuse is independently resettable (i.e., the electronic fuse is operable to or capable of resetting itself) and/or the resettable electronic fuse can be reset by a separate, external component (e.g., a device controller, a battery pack, a battery pack charger, etc.). For example, the resettable electronic fuse can be electrically and/or communicatively connected to a controller of the device  300  such that the resettable electronic fuse provides signals to the controller or receives signals from the controller. The controller of the device  300  is configured to receive, for example, a signal from the resettable electronic fuse indicating that the resettable electronic fuse has tripped. The controller of the device  300  is also configured to generate and transmit a signal to the resettable electronic fuse to reset the electronic fuse. In some embodiments, the controller of the device  300  is also configured to generate and transmit a signal to the resettable electronic fuse to trip or open the resettable electronic fuse. For example, the controller of the device  300  can sense or monitor a parameter of the device  300  (e.g., input current, temperature, etc.) for a fault condition and, based on the sensed or monitored parameter, provide a signal to the resettable electronic fuse that causes the resettable electronic fuse to trip or open. 
       FIG.  4    illustrates a control system for the device  300 . The control system includes a controller  400 . The controller  400  is electrically and/or communicatively connected to a variety of modules or components of the device  300 . For example, the illustrated controller  400  is electrically connected to a motor  405 , a battery pack interface  410 , a trigger switch  415  (connected to a trigger  420 ), one or more sensors or sensing circuits  425 , one or more indicators  430 , a user input module  435 , a power input module  440 , a resettable electronic fuse  445 , and a FET switching module  450  (e.g., including a single stitching FET for a brushed motor or a plurality of switching FETs for a brushless motor). The controller  400  includes combinations of hardware and software that are operable to, among other things, control the operation of the device  300 , monitor the operation of the device  300 , activate the one or more indicators  430  (e.g., an LED), etc. The resettable electronic fuse  445  is connected between the battery pack interface  410  and the FET switching module  450 . 
     The controller  400  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  400  and/or the device  300 . For example, the controller  400  includes, among other things, a processing unit  455  (e.g., a microprocessor, a microcontroller, or another suitable programmable device), a memory  460 , input units  465 , and output units  470 . The processing unit  455  includes, among other things, a control unit  475 , an ALU  480 , and a plurality of registers  485  (shown as a group of registers in  FIG.  4   ), and is implemented using a known computer architecture (e.g., a modified Harvard architecture, a von Neumann architecture, etc.). The processing unit  455 , the memory  460 , the input units  465 , and the output units  470 , as well as the various modules or circuits connected to the controller  400  are connected by one or more control and/or data buses (e.g., common bus  490 ). The control and/or data buses are shown generally in  FIG.  4    for illustrative purposes. The use of one or more control and/or data buses for the interconnection between and communication among the various modules, circuits, and components would be known to a person skilled in the art in view of the invention described herein. 
     The memory  460  is a non-transitory computer readable medium and includes, for example, a program storage area and a data storage area. The program storage area and the data storage area can include combinations of different types of memory, such as a ROM, a RAM (e.g., DRAM, SDRAM, etc.), EEPROM, flash memory, a hard disk, an SD card, or other suitable magnetic, optical, physical, or electronic memory devices. The processing unit  455  is connected to the memory  460  and executes software instructions that are capable of being stored in a RAM of the memory  460  (e.g., during execution), a ROM of the memory  460  (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or a disc. Software included in the implementation of the device  300  can be stored in the memory  460  of the controller  400 . The software includes, for example, firmware, one or more applications, program data, filters, rules, one or more program modules, and other executable instructions. The controller  400  is configured to retrieve from the memory  460  and execute, among other things, instructions related to the control processes and methods described herein. In other constructions, the controller  400  includes additional, fewer, or different components. 
     The battery pack interface  410  includes a combination of mechanical components (e.g., rails, grooves, latches, etc.) and electrical components (e.g., one or more terminals) configured to and operable for interfacing (e.g., mechanically, electrically, and communicatively connecting) the device  300  with a battery pack (e.g., the battery pack  100 ). For example, power provided by the battery pack  100  to the device  300  is provided through the battery pack interface  410  to the power input module  440 . The power input module  440  includes combinations of active and passive components to regulate or control the power received from the battery pack  100  prior to power being provided to the controller  400 . The battery pack interface  410  also supplies power to the FET switching module  450  through the resettable electronic fuse  445  to be switched by the switching FETs to selectively provide power to the motor  405 . The battery pack interface  410  also includes, for example, a communication line  495  for provided a communication line or link between the controller  400  and the battery pack  100 . In some embodiments, the controller  400  is also electrically and/or communicatively connected to the resettable electronic fuse  445  via a signal line. 
     The indicators  430  include, for example, one or more light-emitting diodes (“LEDs”). The indicators  430  can be configured to display conditions of, or information associated with, the device  300 . For example, the indicators  430  are configured to indicate measured electrical characteristics of the device  300 , the status of the device, the status of the resettable electronic fuse  445 , etc. The user input module  435  is operably coupled to the controller  400  to, for example, select a forward mode of operation or a reverse mode of operation, a torque and/or speed setting for the device  300  (e.g., using torque and/or speed switches), etc. In some embodiments, the user input module  435  includes a combination of digital and analog input or output devices required to achieve a desired level of operation for the device  300 , such as one or more knobs, one or more dials, one or more switches, one or more buttons, etc. 
     The controller  400  is configured to determine whether a fault condition of the device  300  is present and generate one or more control signals related to the fault condition. For example, the sensors  425  include one or more current sensors, one or more speed sensors, one or more Hall Effect sensors, one or more temperature sensors, etc. The controller  400  calculates or includes, within memory  460 , predetermined operational threshold values and limits for operation of the device  300 . For example, when a potential thermal failure (e.g., of a FET, the motor  405 , etc.) is detected or predicted by the controller  400 , power to the motor  405  can be limited or interrupted until the potential for thermal failure is reduced. If the controller  400  detects one or more such fault conditions of the device  300  or determines that a fault condition of the device  300  no longer exists, the controller  400  is configured to provide information and/or control signals to another component of the battery pack  100  (e.g. the battery pack interface  410 , the indicators  430 , the resettable electronic fuse  445 , etc.). The signals can be configured to, for example, trip or open the resettable electronic fuse  445 , reset the resettable electronic fuse  445 , etc. In some embodiments, the resettable electronic fuse  445  is configured to independently sense or monitor a parameter of the device  300  and independently trip or open based on the sensed or monitored parameter. 
       FIG.  5    illustrates a battery pack charger  500  that includes a resettable electronic fuse or e-fuse. The battery pack charger  500  includes a housing  505  and interface portions  510 ,  515  for connecting the battery pack charger  500  to one or more battery packs (e.g., battery pack  100 ). The resettable electronic fuse is configured to, for example, disable current out of the battery pack charger  500  by opening a current path of the battery pack charger  500 . As described above with respect to the battery pack  100 , in some embodiments, the resettable electronic fuse is a discrete component that includes a casing or housing and one or more inputs and one or more outputs for passing current. In other embodiments, the resettable electronic fuse does not include a casing or a housing and the resettable electronic fuse&#39;s circuitry is generally exposed. In some embodiments, the resettable electronic fuse is connected to a PCB as a singular unit. In other embodiments, a plurality of discrete components are individually connected to a PCB and connected such that the plurality of discrete components collectively form a resettable electronic fuse. In some embodiments, the battery charger  500  includes a plurality of resettable electronic fuses. 
     The resettable electronic fuse is independently resettable (i.e., the electronic fuse is operable to or capable of resetting itself) and/or the resettable electronic fuse can be reset by a separate, external component (e.g., a battery pack charger controller, a power tool, a battery pack, etc.). For example, the resettable electronic fuse can be electrically and/or communicatively connected to a controller of the battery pack charger  500  such that the resettable electronic fuse provides signals to the controller or receives signals from the controller. The controller of the battery pack charger  500  is configured to receive, for example, a signal from the resettable electronic fuse indicating that the resettable electronic fuse has tripped. The controller of the battery pack charger  500  is also configured to generate and transmit a signal to the resettable electronic fuse to reset the electronic fuse. In some embodiments, the controller of the battery pack charger  500  is also configured to generate and transmit a signal to the resettable electronic fuse to trip or open the resettable electronic fuse. For example, the controller of the battery pack charger  500  can sense or monitor a parameter of the battery pack charger  500  (e.g., output current, temperature, etc.) for a fault condition and, based on the sensed or monitored parameter, provide a signal to the resettable electronic fuse that causes the resettable electronic fuse to trip or open. 
       FIG.  6    illustrates a control system for the battery pack charger  500 . The control system includes a controller  600 . The controller  600  is electrically and/or communicatively connected to a variety of modules or components of the battery pack charger  500 . For example, the illustrated controller  600  is electrically connected to a fan  605 , a battery pack interface  610  (e.g., interface portions  515 ,  520 ), one or more sensors or sensing circuits  615  (e.g., current sensors, temperature sensors, etc.), one or more indicators  620 , a power input circuit  625 , and a fan control module or circuit  635 . The controller  600  includes combinations of hardware and software that are operable to, among other things, control the operation of the battery pack charger  500 , determine a temperature of a heatsink, activate the indicators  620  (e.g., one or more LEDs), etc. 
     The controller  600  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  600  and/or battery pack charger  500 . For example, the controller  600  includes, among other things, a processing unit  640  (e.g., a microprocessor, a microcontroller, or another suitable programmable device), a memory  645 , input units  650 , and output units  655 . The processing unit  640  includes, among other things, a control unit  660 , an ALU  665 , and a plurality of registers  670  (shown as a group of registers in  FIG.  6   ), and is implemented using a known computer architecture (e.g., a modified Harvard architecture, a von Neumann architecture, etc.). The processing unit  640 , the memory  645 , the input units  650 , and the output units  655 , as well as the various modules or circuits connected to the controller  600  are connected by one or more control and/or data buses (e.g., common bus  675 ). The control and/or data buses are shown generally in  FIG.  6    for illustrative purposes. The use of one or more control and/or data buses for the interconnection between and communication among the various modules, circuits, and components would be known to a person skilled in the art in view of the invention described herein. 
     The memory  645  is a non-transitory computer readable medium and includes, for example, a program storage area and a data storage area. The program storage area and the data storage area can include combinations of different types of memory, such as a ROM, a RAM (e.g., DRAM, SDRAM, etc.), EEPROM, flash memory, a hard disk, an SD card, or other suitable magnetic, optical, physical, or electronic memory devices. The processing unit  640  is connected to the memory  645  and executes software instructions that are capable of being stored in a RAM of the memory  645  (e.g., during execution), a ROM of the memory  645  (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or a disc. Software included in the implementation of the battery pack charger  500  can be stored in the memory  645  of the controller  600 . The software includes, for example, firmware, one or more applications, program data, filters, rules, one or more program modules, and other executable instructions. The controller  600  is configured to retrieve from the memory  645  and execute, among other things, instructions related to the control processes and methods described herein. In other constructions, the controller  600  includes additional, fewer, or different components. 
     The battery pack interface  610  includes a combination of mechanical components (e.g., rails, grooves, latches, etc.) and electrical components (e.g., one or more terminals) configured to and operable for interfacing (e.g., mechanically, electrically, and communicatively connecting) the battery pack charger  500  with a battery pack (e.g., battery pack  100 ). For example, the battery pack interface  610  is configured to receive power through the resettable electronic fuse  630  via a power line between the power input circuit  625  and the battery pack interface  610 . The battery pack interface  610  is also configured to communicatively connect to the controller  600  via a communications line  680 . In some embodiments, the controller  600  is also electrically and/or communicatively connected to the resettable electronic fuse  630  via a signal line. 
     The controller  600  is configured to determine whether a fault condition of the battery pack charger  500  is present and generate one or more control signals related to the fault condition. For example, the sensors  615  include one or more current sensors, one or more temperature sensors, etc. The controller  600  is configured to detect an over current condition (e.g., when charging the battery pack  100 ), an over temperature condition, etc. If the controller  600  detects one or more fault conditions of the battery pack charger  500  or determines that a fault condition of the battery pack charger no longer exists, the controller  600  is configured to provide information and/or control signals to another component of the battery pack charger  500  (e.g. the battery pack interface  610 , the resettable electronic fuse  630 , etc.). The signals can be configured to, for example, trip or open the resettable electronic fuse  630 , reset the resettable electronic fuse  630 , etc. In some embodiments, the resettable electronic fuse  630  is configured to independently sense or monitor a parameter of the battery pack charger  500  and independently trip or open based on the sensed or monitored parameter. 
       FIG.  7    illustrates a resettable electronic fuse or e-fuse, such as the resettable electronic fuse  230 ,  445 , or  630  described above with respect to  FIGS.  2 ,  4 , and  6   , respectively. The resettable electronic fuse  230 ,  445 ,  630  includes a casing or housing  700 . In the illustrated embodiment of the resettable electronic fuse  230 ,  445 ,  630 , the resettable electronic fuse  230 ,  445 ,  630  is a discrete component that includes a first input/output pin  705 , a second input/output pin  710 , and a third input/output pin  715 . In some embodiments, the first input/output pin  705  and the second input/output pin  710  are configured to pass current unidirectionally or bidirectionally depending upon the application in which the resettable electronic fuse  230 ,  445 ,  630  is implemented. For example, the resettable electronic fuse  230  implemented in the battery pack  100  is configured to pass current bidirectionally (i.e., during charging and discharging) to provide protection to the battery pack  100  when current is received by the battery pack  100  or discharged from the battery pack  100 . In other embodiments, the resettable electronic fuse  230  is configured to pass current unidirectionally in a charging current path or a discharging current path. In some embodiments, the third input/output pin  715  is configured to provide a reference signal to the resettable electronic fuse  230 ,  445 ,  630 . For example, the third input/output pin  715  can be configured to provide a reference signal related to an overcurrent condition of the battery pack  100  that causes the resettable electronic fuse  230  to trip or open to stop or interrupt electric current passing through the resettable electronic fuse  230 . 
     Although the resettable electronic fuse  230 ,  445 ,  630  is illustrated in  FIG.  7    as including a casing or housing  700  (e.g., as an integrated circuit with enclosed circuitry), in other embodiments, the resettable electronic fuse  230 ,  445 ,  630  does not include the casing or a housing  700 . In such embodiments, the resettable electronic fuse  230 ,  445 ,  630 ′s circuitry is generally exposed. The circuitry associated with the resettable electronic fuse  230 ,  445 ,  630  includes a driver module or driver circuit  720  (e.g., a bootstrap circuit, a charge pump circuit, etc.), a sensing circuit  725  (e.g., an operational amplifier configured as a current sensor, a current mirror, etc.), a comparing circuit  730  (e.g., an operational amplifier configured as a comparator), a first semiconductor switch  735  (e.g., an N- or P-channel MOSFET), and a second semiconductor switch  740  (e.g., an N- or P-channel MOSFET). In some embodiments, the resettable electronic fuse  230 ,  445 ,  630  includes only a single semiconductor switch. The first semiconductor switch  735  and second semiconductor switch  740  each include a first state in which current is able to pass through the switch (e.g., an ON state, a conductive state, etc.) and a second state in which current is not able to pass through the switch (e.g., an OFF state, a non-conductive state, etc.). 
     The resettable electronic fuse  230 ,  445 ,  630  is configured to monitor for and identify a fault condition. For example, the sensing circuit  725  can be configured to sense a current passing through the first semiconductor switch  735  and/or the second semiconductor switch  740 . An output signal from the sensing circuit  725  is provided as an input to the comparing circuit  730 . The comparing circuit  730  also receives a reference signal from the third input/output pin  715 . The reference signal corresponds, for example, to a reference current or current limit value (e.g., a overcharge current signal, an overdischarge current signal, etc.). In some embodiments, the reference signal is a fixed reference signal set using a combination of electrical and electronic components (e.g., a resistor divider circuit). In other embodiments, the reference signal is provided from a controller (e.g., controller  200 ,  400 ,  600 ) and can be modified or adjusted based on one or more conditions. For example, the controller  200 ,  400 ,  600  can include a plurality of reference signal values stored in memory  240 ,  460 ,  645 , respectively, and the controller  200 ,  400 ,  600  is configured to output a determined or selected reference signal based on an operational condition of the battery pack  100 , the device  300 , or the battery pack charger  500 . In some embodiments, the operational condition is a temperature, a voltage, and/or a current. 
     The comparing circuit  730  is configured to compare the received reference signal to the output of the sensing circuit  725 . If, for example, a sensed current is greater than a reference current or current limit value that corresponds to the received reference signal, the comparing circuit  730  outputs a signal to the driver circuit  720  for controlling the first semiconductor switch  735  and/or the second semiconductor switch  740 . In some embodiments, the output signal from the comparing circuit  730  causes the driver circuit  720  to open the first semiconductor switch  735  and/or the second semiconductor switch  740 . In other embodiments, the output signal from the comparing circuit  730  causes the driver circuit  720  to close the first semiconductor switch  735  and/or the second semiconductor switch  740 . As a result, the output signal from the comparing circuit  730  is operable or configured to trip or reset the resettable electronic fuse  230 ,  445 ,  630 . In some embodiments, the driver circuit  720  also includes a timer or counter for resetting the resettable electronic fuse  230 ,  445 ,  630  after an amount of time has elapsed (e.g., sufficient time for an overcurrent condition to have ended). In other embodiments, the driver circuit  720  (or controller  200 ,  400 ,  600 ) is configured to average a predetermined number of past sensed values (e.g., sensed current) to determine when a running average of the sensed values over the predetermined number of sensed values (e.g., 2, 3, 5, 10, or more sensed values) or predetermined time period (e.g., less than one second, greater than one second, less than two seconds, etc.) is less than the reference signal (e.g., to introduce hysteresis). 
     The resettable electronic fuse  230 ,  445 ,  630  illustrated in  FIG.  7    also includes a fourth input/output pin  745  connected to the driver circuit  720 . The fourth input/output pin  745  is connected, for example, to the controller  200 ,  400 ,  600  such that the controller  200 ,  400 ,  600  can provide a signal to the driver circuit  720  that causes the driver circuit  720  to control the first semiconductor switch  735  and/or the second semiconductor switch  740 . In some embodiments, the fourth input/output pin  745  is used to control the resettable electronic fuse  230 ,  445 ,  630  based on a condition different from or redundant to a condition that the resettable electronic fuse  230 ,  445 ,  630  is configured to monitor. For example, the resettable electronic fuse  230 ,  445 ,  630  can be configured to monitor electric current. The battery pack  100 , the device  300 , or the battery pack charger  500  in which the resettable electronic fuse  230 ,  445 ,  630  is implemented is configured to further sense or monitor other parameters or conditions of the battery pack  100 , the device  300 , or the battery pack charger  500  (e.g., e.g., over-temperature, under-temperature, overvoltage, undervoltage, etc.). In some embodiment, the controller  200 ,  400 ,  600  is configured to monitor a temperature of one or more semiconductor switches (e.g., the first semiconductor switch  735  and/or the second semiconductor switch  740 ) or integrated circuits (e.g., the resettable electronic fuse  230 ,  445 ,  630 ). If, after comparing the sensed parameter or condition to a reference value, a fault condition of the battery pack  100 , the device  300 , or the battery pack charger  500  is detected by the controller  200 ,  400 ,  600 , respectively, the controller  200 ,  400 ,  600  is configured to provide a signal to the fourth input/output pin  745  to correspondingly control the resettable electronic fuse  230 ,  445 ,  630 . If the resettable electronic fuse  230 ,  445 ,  630  is used to monitor current, one of the semiconductor switches  735 ,  740  is used to monitor current, the temperature of the device, the resettable electronic fuse  230 ,  445 ,  630 , the semiconductor switch  735 ,  740 , etc., can be used to adjust either the monitored current signal or the current threshold for comparison (e.g., to avoid an erroneous trip). 
     The control action taken by the resettable electronic fuse  230 ,  445 ,  630  based on the signal received at the fourth input/output pin  745  can be to open the first semiconductor switch  735  and/or the second semiconductor switch  740  or to close the first semiconductor switch  735  and/or the second semiconductor switch  740 . As a result, the signal received at the fourth input/output pin  745  is operable or configured to trip or reset the resettable electronic fuse  230 ,  445 ,  630 . For example, the controller  200 ,  400 ,  600  is configured to cause the resettable electronic fuse  230 ,  445 ,  630  to be tripped when a fault condition is detected. The controller  200 ,  400 ,  600  is then configured to cause the resettable electronic fuse  230 ,  445 ,  630  to be reset when the fault condition has ended (e.g., based on one or more sensed signals, a timer or counter, etc.). In some embodiments, the signal received at the fourth input/output pin  745  is used to control a slew rate (e.g., an electrical current slew rate) by controlling gate voltages of the first semiconductor switch  735  and/or the second semiconductor switch  740  to limit the rate at which an electrical current passing through the resettable electronic fuse  230 ,  445 ,  630  changes. In some embodiments, the resettable electronic fuse  230 ,  445 ,  630  is used to control a current or voltage in place of a power or control switch. For example, the resettable electronic fuse  230 ,  245 ,  630  can be used to control a pulse-width modulation (“PWM”) signal to control an amount of current provided to the device  300 , an amount of current received from the battery pack charger  500 , etc. 
       FIG.  8    is a process  800  for operating a resettable electronic fuse, such as the resettable electronic fuse  230 ,  445 ,  630 . The process  800  begins with monitoring a parameter of a device (STEP  805 ). The device is, for example, the battery pack  100 , the device  300 , or the battery pack charger  500 . The monitoring of the parameter can be performed by the resettable electronic fuse  230 ,  445 ,  630  (e.g., current monitoring, etc.) and/or by the controller  200 ,  400 ,  600  (e.g., temperature monitoring, voltage monitoring, etc.). If, at STEP  810 , the monitored parameter is not indicative of a fault condition of the device, the process  800  continues to monitor the parameter at STEP  805 . If, at STEP  810 , the monitored parameter has a value that is indicative of a fault condition of the device, the process  800  proceeds to STEP  815  where an interrupt signal is generated. The interrupt signal can be generated within the resettable electronic fuse  230 ,  445 ,  630  (e.g., by comparing circuit  730 ) or can be generated externally to the resettable electronic fuse  230 ,  445 ,  630  (e.g., by controller  200 ,  400 ,  600 ). 
     After the interrupt signal is generated at STEP  815 , the interrupt signal is received, for example, by the driver circuit  720  and the driver circuit  720  causes the first semiconductor switch  735  and/or the second semiconductor switch  740  to be turned OFF or opened (STEP  820 ). In some embodiments, the first semiconductor switch  735  and/or the second semiconductor switch  740  are turned OFF to prevent current from passing through the resettable electronic fuse  230 ,  445 ,  630 . In other embodiments, the first semiconductor switch  735  and/or the second semiconductor switch  740  are turned OFF and back ON again to limit or control the current passing through the resettable electronic fuse  230 ,  445 ,  630 . 
     After the driver circuit  720  has caused the first semiconductor switch  735  and/or the second semiconductor switch  740  to be turned OFF or opened at STEP  820 , the resettable electronic fuse waits to be reset (STEP  825 ). The resettable electronic fuse  230 ,  445 ,  630  can generate a reset signal itself (e.g., as an output of the comparing circuit  730 , based on a timer in the driver circuit  720 , etc.), and/or the resettable electronic fuse  230 ,  445 ,  630  can receive a reset single from another component (e.g., controller  200 ,  400 ,  600 ). When a reset signal is received by the driver circuit  720 , the resettable electronic fuse  230 ,  445 ,  630  is reset by causing the first semiconductor switch  735  and/or the second semiconductor switch  740  to be turned ON or closed. The process  800  then returns to STEP  805  where the parameter of the device is again monitored. In some embodiments, the monitoring of the parameter of the device at STEP  805  is a continuous monitoring of the parameter of the device. For example, the monitoring of the parameter of the device continues after the first semiconductor switch  735  and/or the second semiconductor switch  740  to be turned OFF or opened at STEP  820 . By continuing to monitor the parameter of the device, the resettable electronic fuse  230 ,  445 ,  630  or another component (e.g., controller  200 ,  400 ,  600 ) is able to determine when a fault condition has ended and is no longer present. Detecting that the fault condition has ended or is no longer present can then cause the reset signal for the resettable electronic fuse to be generated. 
     Thus, embodiments described herein provide a resettable electronic fuse for a device (e.g., a high-power device), such as a power tool, a battery pack for the power tool, or a battery pack charger. Various features and advantages are set forth in the following claims.