Abstract:
A technique for prolonging the life of a rechargeable battery in a computer is disclosed, wherein an automatic discharging and charging cycle occurs only during a time when the user does not anticipate ever needing to operate the computer using the battery. In another technique for prolonging the life of a rechargeable battery, to eliminate frequent topping off of the battery&#39;s charge by the computer&#39;s recharging routine, the battery is only automatically topped off after a relatively long interval if the computer remains plugged in. Such topping off may occur after the battery charge has fallen to a certain charge level or only after an extended time period. The time period may be set by the user. By topping off less frequently, the battery life is extended.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to devices incorporating a rechargeable battery, such as computers and wireless phones.  
         BACKGROUND  
         [0002]    U.S. Pat. No. 6,463,545, incorporated by reference in its entirety, describes a battery calibration technique. The &#39;545 patent describes discharging a rechargeable battery in a laptop computer to substantially zero charge in order for the computer&#39;s charge detection circuits to accurately determine the amount of computer operating time left before the battery power runs out. While the computer is plugged into an AC outlet, a calibration circuit automatically initiates a calibration mode, whereby the main power source is decoupled from the computer, and the battery supports the computer operation until the battery discharges to a level slightly above a zero charge. This is considered a zero state, which is then used to calibrate the power management software so that the software can better determine how much battery time is left before the computer is forced to be shut down. The main power supply is then automatically reconnected to the computer, and the battery is charged normally until the battery is fully charged. After some period, not identified in the &#39;545 patent, the calibration technique is again commenced.  
           [0003]    A scenario given in the &#39;545 patent is that the calibration technique occurs during normal computer operation when the computer is turned on and in use. However, it may be disastrous for the laptop computer operator to decide to unplug the computer from the wall during the middle of the calibration sequence and continue her work on the laptop at another location. Since the calibration sequence occurs without user intervention, the user may unplug the AC connection only to find that the battery is virtually dead due to the interruption of the calibration sequence.  
         SUMMARY  
         [0004]    One embodiment of the present invention augments the invention in the &#39;545 patent by only performing the automatic discharging and charging cycle during a time window authorized by the user. Such an authorized time window will most likely be a time in the middle of the night when the user does not anticipate ever using the computer unplugged from the AC outlet. Hence, if the computer is plugged into an AC outlet, the controller for the automatic discharging and charging technique reads the time of day clock in the computer, compares this clock to the authorized time window for performing the technique, and initiates the technique if the time of day falls within the authorized time window.  
           [0005]    It is well known that a battery&#39;s life is prolonged if it is periodically fully discharged and recharged. This relates to the memory effect of the battery. Thus, the automatic discharging and charging of the battery not only calibrates the power management system but prolongs the life of the battery while not interfering with the use of the computer.  
           [0006]    In another embodiment, the automatic discharging and charging technique is not related to calibration, but is performed periodically to prolong the life of the battery.  
           [0007]    In another embodiment, the authorized time window for performing the discharging and charging technique is a default time that is intended to occur at a time when the computer is typically not in use.  
           [0008]    In another embodiment, additional techniques are used to increase the life of the battery. As mentioned above, it is known that batteries should be discharged to a low level periodically in order that they can retain a greater charge, in contrast to a battery that is constantly being topped off without first being significantly discharged. For example, when a laptop computer is plugged into the wall for long periods of time, the battery is continually or periodically being topped off. Such a battery will have a shorter useful lifetime then a battery that had been occasionally discharged by the user unplugging the computer from the wall and plugging the computer back into the wall when the “low battery” alarm was signaled in the computer. To eliminate such frequent topping off, a method is carried out whereby the battery is only automatically topped off after a relatively long interval if the computer remains plugged in. Such topping off may occur after the battery charge has fallen to a certain charge level or only after an extended time period. The time period may be set by the user. Accordingly, by topping off less frequently, the battery life is extended.  
           [0009]    The present invention is not limited to computers, but is generally applicable to all devices incorporating a rechargeable battery. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic diagram of the power management portion of a device, such as a computer.  
         [0011]    [0011]FIG. 2 is a flowchart of a method performed by the circuit of FIG. 1.  
         [0012]    [0012]FIG. 3 is a simplified diagram of a computer system, or other apparatus, where a resistive load may be coupled to the battery to discharge the battery.  
         [0013]    [0013]FIG. 4 is a flowchart of a method to limit the frequency of topping off the battery. 
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 is similar to FIG. 2 of U.S. Pat. No. 6,463,545, previously described, except that I/O controller  160  also senses a time of day from clock  162  (or an internal clock) and only initiates a discharge/charge cycle at times authorized by the user. The remainder of the elements in FIG. 1 are described in detail in the &#39;545 patent, so a detailed explanation of those prior art elements is not necessary.  
         [0015]    [0015]FIG. 1 illustrates a power subsystem  200  for a device such as a computer or telephone. Subsystem  200  includes a conventional power supply  204 . Power supply  204  generally comprises a rectifier and smoothing circuit for converting a wall outlet AC voltage into an unregulated DC voltage. This unregulated DC voltage is applied to a voltage regulator that outputs a fixed DC voltage, such as 18 volts. The voltage regulator will typically be a switching voltage regulator that uses either current mode or voltage mode techniques.  
         [0016]    A switch  220  is normally closed for coupling a system power bus  222  to the power supply  204 . A computer or other load is connected to the power bus  222 . Power subsystem  200  is typically located within the computer body.  
         [0017]    The I/O controller  160  interfaces various input devices, including a power switch and a suspend switch, and handles power management functions such as reducing power to various components such as the display, floppy drive, hard disk drive, and various other circuits to place the computer into a low power sleep mode. Controller  160  is connected to a bus  223  that communicates with a microprocessor and registers in battery  202  to select the operating mode of battery  202  (e.g., charge, discharge, idle) and read the status of the various registers, including a charge register.  
         [0018]    Bridge logic  168  couples various buses together and shares power management functions with I/O controller  160 , as described in the &#39;545 patent. The functions required to carry out the present invention are relatively simple, and the circuitry of FIG. 1 may be simplified yet still carry out the invention.  
         [0019]    The operation of the circuit of FIG. 1 will be described with respect to the flowchart of FIG. 2.  
         [0020]    In step  300  of FIG. 2, upon setting up of the computer, the user is prompted to enter a period of time, such as a four hour window, in which the user authorizes the computer&#39;s power subsystem  200  to enter into an automatic discharging and charging routine to extend the life of the battery and optionally calibrate the battery life detector. The user will most likely select a window in the middle of the night when the user is not likely to unplug the computer from wall current and use the computer. The user may enter the time window via the computer&#39;s keyboard or by clicking on an icon with a mouse. This window is then stored in a memory that is accessible by the I/O controller  160 . The memory may be internal to I/O controller  160 .  
         [0021]    The computer manufacturer determines the optimum period between the automatic discharging/charging cycles, such as once per week, and this information is also stored in a memory. This value may instead be set by the user and may depend on the recommendations of the battery manufacturer. In another embodiment, the optimum period is stored in the battery&#39;s memory by the manufacturer.  
         [0022]    In steps  302 ,  304 , and  306 , I/O controller  160  detects the current date and time from clock  162 . Clock  162  may provide its time and date signal via a bus, or the clock may be internal to I/O controller  160 . I/O controller  160  determines whether all three of the following conditions are occurring: 1) the period set by the manufacturer for the automatic discharging/charging cycle has elapsed; 2) the computer is receiving AC current (detected on line  226 ); and 3) the time of day is within the authorized window set by the user. If all these conditions occur, I/O controller  160  (or any other device involved with initiating the routine) transmits a signal to logic  168  to initiate the discharge/charging cycle. If the time of day is not within the authorized window, the discharge/charge cycle is delayed (step  306 ) until the time window occurs.  
         [0023]    Assuming all three conditions are met, I/O controller  160  issues a discharge/charge signal to bridge logic  168  via line  228 . In response, bridge logic  168  pulls line  224  high. This high signal opens switch  212  and controls logic  208  to open up switch  220  (step  308 ). Opening up switch  220  causes the battery  202  charge to drain into the load (e.g., the computer components) coupled to the power bus  222 . Opening switch  212  causes the master battery signal to be solely dependent on the charge status of battery  202 , as described in the &#39;545 patent. Battery  202  generates a high master battery signal when there is adequate charge to power the load.  
         [0024]    In step  310 , battery  202  discharges into the load via power bus  222 . Since I/O controller  160  senses from line  226  that the computer is receiving AC current, I/O controller  160  does not place the computer into a standby, sleep, or hibernate mode when the battery charge goes below a typical low charge threshold (e.g., 3%). Hence, battery  202  can discharge to near zero charge.  
         [0025]    When the battery has about 4 seconds of charge left, battery  202  pulls the master battery level low (step  312 ). In step  314 , this low signal controls logic  208  to close switch  220  to again couple the DC voltage from the power supply  204  to the computer so that the computer has no break in power. The change in master battery level also signals I/O controller  160  to issue a signal to bridge circuit  168  to deassert the discharge/charge cycle signal on line  224 . This closes switch  212 . I/O controller  160  then controls battery  202  via bus  223  to be in the charging mode to fully charge battery (step  316 ). The computer is now in a normal operating mode.  
         [0026]    When the computer is not turned on and operating, very little current is drawn by the computer. The computer will typically be off or in a standby mode during the user-set authorized window. Hence, the discharging of the battery may take days, which is unacceptable. In one embodiment, when the discharge cycle is initiated, I/O controller  160  automatically turns on the computer. This is a simple task since I/O controller  160  is coupled to the main power switch of the computer. Turning on the computer causes the computer to be a high current load, thus rapidly draining battery  202  within approximately 2-3 hours. The signal that turns on the computer during the discharging mode also signals the power management software to ignore the conventional standby and hibernate times typically set by the user. For example, the user may set the standby time, where no action is taken on the computer, to 15 minutes. Normally, if no action is taken on the computer in 15 minutes, the screen, hard drive, and microprocessor are put into a low current mode. This would be overridden by I/O controller  160  during the discharging cycle so that the computer would not go into a standby mode until the entire discharging cycle has been completed. If the user had turned off the computer before the discharge cycle, I/O controller  160  would turn the computer off after the discharge cycle was complete.  
         [0027]    [0027]FIG. 3 is a simplified version of the automatic discharging/charging circuit, where controller  320  interfaces with battery  202  and switch  220  to control the automatic discharging/charging cycle. Controller  320  opens switch  220  at the initiation of the automatic discharging/charging process when the three conditions are met, as discussed above. It may not be advantageous to turn on the computer  322  during the automatic discharging/charging process due to noise, heat, wear and tear, etc. Instead, to quickly drain battery  202 , a resistive load  324  (or other type of load) is coupled to power bus  222  via a switch  326  to drain the battery charge in a few hours. Both switches  220  and  326  may be controlled by the same signal on line  328 . The termination of discharging and the initiation of charging may be performed in the manner previously described.  
         [0028]    An additional feature of the invention may be the recognition by I/O controller  160  (or controller  320  in FIG. 3) that the battery  202  has been recently discharged to a low level and recharged during normal operation of the computer and, thus, the automatic discharging/charging process may be skipped. In such an embodiment, the date/time of the last full discharge is recorded in the I/O controller  160  memory. If the time for the periodic automatic discharge/charge process arises and the battery was recently discharged during its normal operation, I/O controller  160  will skip the automatic discharge/charge operation.  
         [0029]    In another embodiment of the invention, it is recognized that battery life is diminished due to the battery being frequently “topped off” pursuant to typical charging routines for batteries in a laptop computer or other device. Less frequent topping off of the battery when the computer is left plugged in would prolong the battery life. However, the user wants the battery to be fully charged whenever the user disconnects AC power from the computer. Hence, there is a tradeoff between maximizing the battery life and providing a maximum charge for the battery. This dilemma is solved by the method of FIG. 4.  
         [0030]    In step  400  of FIG. 4, during the set up of the computer, the user is prompted by the computer to identify an allowable period between topping off the battery when the computer is plugged into the wall socket. The manufacturer may provide the user with a graph illustrating battery life versus the frequency of topping off. The user then sets the period (e.g., one day) that the power system must wait before again topping off the battery.  
         [0031]    In step  402 , the user sets the charge level threshold (e.g., 90%), whereby the battery will be immediately topped off if the charge (identified by the battery&#39;s charge register) falls below the threshold. The user may input her settings via the computer&#39;s keyboard or a mouse.  
         [0032]    In step  404 , I/O controller  160  determines if the charge in battery  202  is below the threshold. If so, battery  202  is immediately topped off to fully charge battery  202  (step  406 ).  
         [0033]    In step  408 , I/O controller  160  determines if the authorized period for topping off has elapsed. If so, then the normal routine for topping off the battery is performed (step  406 ). Such a normal routine may top off the battery even if the charge is 98%.  
         [0034]    In an alternate embodiment, only the user-set charge threshold is used to reduce the frequency of topping off, and steps  400  and  408  are eliminated.  
         [0035]    Accordingly, the process of FIG. 4 reduces the number of topping off charging cycles, thus prolonging the life of the battery.  
         [0036]    The controllers for the inventive techniques described may be simple logic circuits, easily designed by those skilled in the art.  
         [0037]    The techniques described herein can be applied to any device that uses a rechargeable battery, including wireless phones, such as cell phones and home wireless telephones.  
         [0038]    Having described the invention in detail, those skilled in the art will appreciate that, given the present disclosure, modifications may be made to the invention without departing from the spirit of the inventive concepts described herein. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described.