Patent Publication Number: US-2009230923-A1

Title: Battery management circuit

Description:
TECHNICAL FIELD 
     The following generally relates to a battery management circuit located in/within the housing of a battery, and finds particular application to a non-rechargeable (primary) Lithium-Iron Disulfide (Li—FeS 2 ) battery. 
     BACKGROUND 
     The term battery has referred to a device with one or more electrochemical cells that supply electric current for a load. Generally, batteries come in two types: primary; and secondary. Primary batteries supply energy through an irreversible reaction and cannot/should not be recharged. Secondary batteries, on the other hand, supply energy through a reversible reaction and can be recharged, for example, by supplying a charging current to the battery, in the opposite direction of the discharge current. Both primary and secondary batteries are manufactured in various sizes, chemistries, voltages, and form factors, and are employed to power various battery-powered devices. 
     It has been desirable to automatically, selectively inhibit the current supplied by a primary battery to a battery-powered device. For example, with a flashlight or other electrical device it may be desirable to inhibit current flow from a primary battery to the device when a temperature of the battery and/or the device exceeds a preset temperature threshold. Such a temperature may be indicative of an electrical short within the battery and/or device, excessive current draw by a load, ambient temperature conditions, and/or another temperature based fault condition. To facilitate this, a positive temperature coefficient (PTC) device has been included in a battery in the path of the electrical current. Generally, the resistance of the PTC device is a function of its temperature and abruptly rises when its temperature exceeds a trip threshold, which reduces current flow therethrough. 
     More particularly, the PTC device includes a polymer/graphite matrix sandwiched between metal foil. When the temperature of the PTC device exceeds a trip temperature of about 85 degrees Celsius (° C.), the polymer/graphite expands, thereby increasing its resistance and reducing current. In one instance, the PTC device has a resistance of about 35 milliohms (mΩ) at 20° C. and increases about 0.4 mΩ/° C. up to the trip temperature threshold, at which the resistance increases rapidly up to about 100Ω. When the PTC device cools down below the trip temperature, its resistance tends to resets back towards to a pre-trip resistance state. 
     Unfortunately, the PTC device has several shortcomings. For example, the PTC device trips based solely on its temperature, and there may be other characteristics which would desirably trigger inhibiting current flow. Furthermore, the PTC device, when tripped, merely limits or reduces current (via the 100Ω resistance), but does not stop current flow through the PTC. As such, even during a temperature based fault condition, current continues to be supplied by the battery and the current continues to heat the PTC device. In addition, the PTC device is subject to a trip/reset delay after a fault condition due to the time it takes to heat up/cool down relative to the trip threshold. Further, the PTC device is a passive device and may end up oscillating between low and high resistance states if the temperature of the PTC device oscillates about the threshold temperature. And after a reset, if a reset is even possible, the resistance of the PTC device typically is higher (e.g., about double) than its initial pre-trip resistance, which decreases high rate performance. Moreover, the PTC device is sensitive to compression forces, which may delay or prevent PTC activation. This sensitivity to pressure may also limit the cell design choices, particularly with respect to closures and sealing methods used in high volume production settings. 
     SUMMARY 
     Aspects of the application address the above matters, and others. 
     In one aspect, a non-rechargeable battery includes a housing with an opening and a cover that closes the opening in the housing. The housing and the cover define a volumetric region within the battery. The battery also includes at least one electrochemical cell and a management component, both located in the volumetric region. The management component includes programmable electrical circuitry that selectively interrupts electrical current output from the cell out of the battery based on an actively monitored state of the battery. The chemistry of the battery is Li—FeS 2  or other non-rechargeable chemistry. 
     In another aspect, a method of controlling an electrical current output of a primary battery includes determining an electrical operating characteristic of the primary battery, and executing an executable instruction that causes interruption of the electrical current output of the primary battery based on the electrical operating characteristic. 
     In another aspect, a primary battery includes a cell that stores energy, an output terminal, a switch located between the cell and the output terminal and within the primary battery, wherein the switch includes an active electrical component that is powered by the cell, and a microprocessor that controls the switch so as to prevent electrical current flow from the cell through the switch and to the output terminal under a preset condition, wherein the microprocessor is located within the primary battery. 
     In another aspect, the primary battery further includes an electrical current level sensor that determines a level of the electrical current flow from the cell, and the microprocessor controls the switch so as to prevent electrical current flow through the switch when the level exceeds a preset programmable current level threshold. 
     In another aspect, the primary battery further includes an electrical current direction sensor that determines a direction of the electrical current flow of the cell, and the microprocessor controls the switch so as to prevent electrical current flow through the switch when the direction does not satisfy a preset programmable electrical current direction. 
     In another aspect, the primary battery further includes a temperature sensor that determines a temperature of the battery, and the microprocessor controls the switch so as to prevent electrical current flow through the switch when the temperature exceeds a preset programmable temperature threshold. 
     In another aspect, the primary battery further includes a state of charge determiner that determines a state of charge of the battery, wherein the microprocessor outputs the state of charge through the terminal. 
     In another aspect, the primary battery further includes a power source that powers at least active components of the switch and the microprocessor, wherein the power source uses power from the cell to power the at least active components of the switch and the microprocessor. 
     Those skilled in the art will recognize still other aspects of the present application upon reading and understanding the attached description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  illustrates an example battery; 
         FIG. 2  illustrates the example battery in connection with a battery-powered device; 
         FIG. 3  illustrates an example battery management circuit; 
         FIG. 4  illustrates a first example switch of the battery management circuit; 
         FIG. 5  illustrates a second example switch of the battery management circuit; 
         FIG. 6  illustrates a third example switch of the battery management circuit; 
         FIG. 7  illustrates a flow diagram. 
     
    
    
     DETAILED DESCRIPTION 
     The following relates to a primary battery battery-management circuit that manages the power output by the primary battery. The battery management circuit is described herein in connection with a Lithium-Iron Disulfide (Li—FeS 2 ) disposable battery. However, the battery operation management circuit may be utilized with a different non-rechargeable battery chemistry. A primary battery including the battery management circuit may be used in connection with various battery-powered appliances such as, but not limited to, lighting appliances (e.g., flashlights, table lamps, etc.) and non-lighting electrical appliances (e.g., games, cellular phones, battery life extenders which use primary batteries to recharge one or more secondary batteries on a separate device, digital cameras, computers, etc.). 
     Initially referring to  FIG. 1 , an example battery  100  is illustrated. As noted above, in this example the battery  100  is a Li—FeS 2  primary battery. As shown, the battery  100  includes a housing  102 , including a first portion or can  104  and a second portion or cap  106 , at least one cell  108  and a battery management circuit (mgmt)  110 . The battery  100  may be, for example, an FR6 type cylindrical battery in which the can  104  includes a closed bottom, a closed cylindrical side wall, and an open top that is closed by the cap  106 . Other form factors may also be possible. As defined herein, the battery  100  includes and is enclosed by the can  104  and cap  106 . 
     Given the propensity for organic electrolytes required by Li—FeS 2  cells to dissolve or degrade many materials (and especially plastics), the battery management circuit  110  must be located outside of the chemical region of the cell  108  (i.e., the electrochemically active portions of the cell—anode, cathode and electrolyte), either within the can  104  or as an integrated part of the closure cap  106 . In the illustrated example, the battery management circuit  110  resides in the can  104  between the cell  108  and the cap  106 . In another instance, the battery management circuit  110  may be located at least partially within or outside of the can  104 . In yet another instance, the battery management circuit  110  may be located in the cap  106 . Moreover, in another instance the battery management circuit  110  or an additional battery management circuit  110  may reside between the cell  108  and the can  104 . However, to the extent that many consumer batteries have standardized sizes, it is important that the battery management circuit still occupy as little volume as possible regardless of whether it is carried within the container or attached thereto. 
     It is to be appreciated that the battery management circuit  110  may include one or more active and/or passive components. In addition, the circuit  110  may be implemented in an integrated chip (IC), an application specific integrated chip (ASIC), or otherwise. In each instance, the circuit  110  does not require a passive activation method (i.e., experiencing a set temperature) and instead it actively monitors a condition and then implements a pre-programmed response thereto. In doing so, the circuit will not experience any chemical phase change (as in PTCs), nor does it require any moving parts (as in some memory metal springs). 
     The battery management circuit  110  may be included in addition to or in alternative to one or more other devices of the battery  100  such as a positive temperature coefficient (PTC) device. In one instance, the foot print of the battery management circuit  110  is about the same as or is smaller than the foot print of a PTC device for a battery. In this instance, the battery management circuit  110  may reside in the region allocated for the PTC device or in another region. In another instance, a size of the can  104  and/or the cell  108  is configured so that the cell  108  and the battery management circuit  110  both fit in the can  104 . 
     In the illustrated example, an anode of the cell  108  is in electrical communication with the can  104 , and a cathode of the cell  108  is in electrical communication with the cap  106  through the battery management circuit  110 . In another embodiment, the terminals may be switched so that the anode of the cell  108  is in electrical communication with the cap  106  through the battery operation management circuit  110 , and the cathode of the cell  108  is in electrical communication with the can  104 . Although the terminals of the battery  100  are shown as being located on different sides of the battery  100 , it is to be appreciated that in another embodiment the terminals may be located on a same side of the battery  100 . 
     The battery  100  may also include a pressure relief vent (not shown), including an aperture (not shown) that is selectively sealed by a vent ball (not shown) or the like. When the internal pressure of the cell  108  exceeds a predetermined level, the vent ball is forced out of the aperture to release pressurized fluids from the cell  108 . Other venting devices are possible, including without limitation foil vents or other similar rupturable members. In each case, the battery management circuit  110  must be configured to accommodate the venting device, in terms of having sufficient clearance to allow the outflow of gases and/or the displacement of the ball/laminate member. 
     As noted above, the battery management circuit  110  may also be employed with a battery other than a Li—FeS 2  battery. Non-limiting examples of suitable primary batteries include alkaline (e.g., Zn/MnO 2 ) or carbon zinc (CZn) etc. Battery packs are also contemplated. Significantly, all of these primary systems are designed to be low cost and disposable, such that the use of expensive or complex current interruption devices was not previously seen as feasible or desirable in such primary systems. 
     Turning to  FIG. 2 , the primary battery  100  is shown in connection with a battery-powered device  200 . Such a device  200  may include a battery receiving region configured to receive one or more of the batteries  100 . In this example, the battery  100  supplies power for a load  202 . 
     The battery management circuit  110  may include a microprocessor or the like that executes programmable executable instructions and/or provides various battery management functions. For instance, the battery management circuit  110  selectively interrupts current output by the battery. As used herein, interrupt refers to completely or substantially stopping current flow, as compared to currently available PTC devices and/or memory metal springs which physically deform at predetermined temperature. Nevertheless, there still may be a slight leakage of current through a transistor or the like. 
     The battery management circuit  110  selectively interrupts current output by the battery based on various information and/or states of the battery  100 . For example, the battery management circuit  110  may interrupt current flow based on the magnitude of the current and/or the direction of the current. In another example, the battery management circuit  110  additionally or alternatively interrupts current flow based on the temperature of the battery  100 . In another instance, the battery management circuit  110  provides various information. Such information includes, but is not limited to, the state of charge of the battery  100 . Other management functions are also contemplated. 
     Such management allows the battery  100  to be inherently safe under fault and/or abusive conditions such as, but not limited to, forced discharge, forced charge, etc. In addition, the battery management circuit  110  allows for the following: low resistance during normal operation, high resistance so as to interrupt current flow during an undesirable state, reverse current (charge) prevention, current sensing, fuel gauging, and/or other capabilities. 
       FIG. 3  illustrates an example battery management circuit  110  in connection with the cell  108  and the load  202 . Electrical current from the cell  108  is supplied to the load  202  via a switch  304 . A control component (CTRL)  306  selectively controls the switch  304  based on various inputs such as the current, a direction of the current flow, and a temperature of the battery  100 . The switch  304 , in this instance, may be a current limiting switch. 
     A power component  302  supplies power for active components of the battery management circuit  110 . In the illustrated example, the power component  302  receives power from the cell  108  and supplies suitable power to the active components. In one instance, the power component  302  includes a boost circuit (not shown) to step up the received power. For example, in one embodiment the cell  108  supplies from about 0.5 volts direct current (VDC) to about 1.7 VDC to the power component  302 . The boost circuit of the power component  302  boosts the received voltage to produce an output voltage greater than 1.7 VDC, such as about 5 or 9 VDC. In another embodiment, the boost circuit is configured for another operating voltage range. 
     A current direction sensor  308  senses the direction of the current flowing from the cell  108  through the switch  304  to the load  202 , and generates a signal indicative thereof. The signal is provided to the control component  306 , which invokes the switch  304  based on the signal. In one instance, when the switch  304  allows current to pass through to the load  202 , the signal indicates that the current is flowing in the appropriate direction. In another instance, when current is attempting to flow in the opposite direction, the signal indicates invokes the control component  306  to open the switch. In this instance, current flow through the switch  304  is interrupted or stopped. As such, the switch  304  may behave like an ideal diode in that current is allowed to freely flow in one direction and essentially does not flow in the opposite direction. 
     A current level sensor  310  senses a level of the current flowing from the cell  108  through the switch  304  to the load  202 , and generates a signal indicative thereof. The signal is provided to the control component  306 , which invokes the switch  304  based on the signal. In one instance, the signal indicates that the current level is below a preset threshold current level and the switch  304  allows current to pass through to the load  202 . In another instance, the signal indicates that the current level is above the preset threshold. In this instance, the signal indicates invokes the control component  306  to open the switch  304 , thereby interrupting current flow. 
     A temperature sensor  312  senses the temperature of the battery  100  and generates a signal indicative thereof. An example of a suitable temperature sensor includes a thermocouple. Alternately temperature sensing can be accomplished onboard a semiconductor or ASIC by means of monitoring temperature sensitive portions of the die circuit itself. The signal is provided to the control component  306 , which invokes the switch  304  based on the signal. In one instance, the signal indicates that the temperature is below a preset threshold temperature, which, for example, may indicate that the battery temperature is within operating conditions. In another instance, the signal indicates that the temperature is above the preset threshold. In this instance, the signal invokes the control component  306  to open the switch  304  to interrupt current flow therethrough. The temperature sensor  312  may be configured to continuously, periodically, aperiodically, otherwise sense the temperature. 
     The battery management circuit  110  may also include a coulomb counter  314  and a state of charge (SOC) determiner  316 . The coulomb counter  314  determines a capacity removed during discharge based on the current flow and generates a signal indicative thereof. The SOC determiner  316  generates a signal indicative of the state of charge or the remaining life of the battery  100  based on the signal from the coulomb counter  314 . In the illustrated example, the output of the SOC determiner  316  is provided through the cap  106 . It is to be appreciated that the signal can be provided with various precision such as in quartiles or coarser or finer resolution. The SOC determiner  316  may also be omitted. 
     It is to be appreciated that the battery management circuit  110  may also include memory. Various algorithms and/or instructions may be stored in the memory and executed by the control component  306  and/or another processor. In addition, various information such as historical information, information about the manufacturing process, date(s), current direction, current magnitude, temperature, SOC and/or other information can be stored in the memory and retrieved therefrom, for example, through the cap  106  and/or otherwise. 
       FIGS. 4 ,  5  and  6  illustrate example switches  304 .  FIGS. 4 and 5  show examples including two n-type MOSFETS (Metal Oxide Semiconductor Field Effect Transistors), whereas the example of  FIG. 6  includes a single n-type MOSFET. P-type MOSFETS may alternatively be used. Common Drain, common Source, and/or Drain-Source connected MOSFETS are contemplated. The MOSFETS are controlled to transition between an active and an inactive state, thereby allowing and interrupting current flow. As described in greater detail below, the MOSFETS have relatively low resistance when active and relatively high resistance when inactive, essentially stopping current flow except for the leakage current of the MOSFETS. The MOSFETS also do not dissipate any significant heat when inactive. 
     Initially referring to  FIG. 4 , a common Source configuration is illustrated. In one instance, the two MOSFETS together have a resistance of about 17 mΩ, which is about 50% of the resistance of a PTC device. The leakage current is on the order of about 1 μA (micro-Amphere) to about 350 mA (milli-Amphere). In a forced discharge mode, the two MOSFETS, when off (V gate =0V) have protected that the battery up to about 19 V, with a leakage current less than 1 μA. In reversal mode, the diode was bridged at about 4.5 V. 
     Turning to  FIG. 5 , another common Source example is shown. As above, the two MOSFETS have a resistance of about 17 mΩ. With both forced discharge and reversal modes, the two MOSFETS, when off (V gate =0V) have protected that the battery up to about 19 V, with a leakage current of about 1 μA. 
     In a p-type MOSFET example, the two MOSFETS again have a resistance of about 17 mΩ. With both forced discharge and reversal modes, the two MOSFETS, when off (V gate =0V) has protected that the battery up to about 19 V, with a leakage current of about 1 μA. 
     It is to be appreciated that the MOSFETS may alternatively be configured in a parallel configuration, reducing their aggregate resistance to about 10 mΩ. 
       FIG. 6  shows an example of a single MOSFET switch  304 . In this example, the MOSFET has a resistance of about 9 mΩ. The leakage current, when the switch is off (V gate =9V), is less than about 1 mA. 
     Other types of FETS and/or active components are also contemplated. 
     Operation is illustrated in connection with  FIG. 7 . It is to be appreciated that the order of below acts is not limiting and the acts may be performed in a different order. In addition one or more of the acts may be omitted and/or one or more additional acts may be added. 
     At  702 , the direction of the current flow is sensed. At  704 , if the direction of the current indicates a charging state, then current flow is interrupted at  706 . Otherwise, current can still flow. 
     At  708 , the current is sensed. At  710 , if the current is greater than a temperature threshold, then current flow is interrupted, reduced or pulsed at  706 , for example, so that the time average current is less than pre-determined, critical value, thereby allowing the battery to cool down. Otherwise, current can still flow. 
     At  712 , the temperature of the battery is sensed. At  714 , if the temperature is greater than a temperature threshold, then current flow is interrupted at  706 . Otherwise, current can still flow. 
     At  716 , the state of charge of the battery is determined, and at  718  the state of charge is output through a terminal of the battery. The output voltage of the battery could carry a superimposed information signal on top of the main battery voltage and associated power to the device. This information could be in the form of Pulse Width Modulated (PWM) or Pulse Frequency Modulated (PFM) signal or other binary encoded signal implemented by varying the output voltage of the battery by means of the FETs from some standard level (1.5V) to some other level 1.0V for a period of time such that information about the battery (such as SOC) can be communicated without causing a power interruption on the down stream device. This can be implemented in a variety of ways including but not limited to the use of analog to digital converters or comparators on the down stream device to sense the variations in incoming voltage (the superimposed information). 
     The application has been described with reference to various embodiments. Modifications and alterations will occur to others upon reading the application. It is intended that the invention be construed as including all such modifications and alterations, including insofar as they come within the scope of the appended claims and the equivalents thereof.