Patent Publication Number: US-2005134222-A1

Title: Charging control for battery powered devices

Description:
This application is related to, and claims priority to U.S. provisional application No. 60/530,543, filed Dec. 18, 2003, entitled “Charging Control Circuit For Notebooks”, Attorney Docket Number P1930US00, the entirety of which is incorporated by reference herein, including all of the documents referenced therein. 
    
    
     FIELD OF THE INVENTION  
      The present invention generally relates to the field of charging power sources in portable equipment.  
     BACKGROUND OF THE INVENTION  
      Portable electronic devices often have rechargeable power sources such as batteries. Many portable devices provide circuitry for recharging these power sources when auxiliary sources of power are available, perhaps AC line voltage. Presently, when an auxiliary power source is connected to an electronic device having a rechargeable power source and associated charging circuit, the charging circuit initiates a charge cycle. Unfortunately, most rechargeable batteries degrade with each recharge cycle and are generally rated by the number of recharge cycles that can be performed before the battery can hold only around one half its original power capacity. Generally, it does not make a significant difference in degradation whether a battery is recharged from a fully discharged state or from an almost fully charged state.  
      Many usage scenarios for portable electronic devices include disconnecting the electronic device from an auxiliary power source, then using the electronic device for a limited a mount of time while disconnected, then re-connecting the electronic device to the auxiliary power source. For example, one may take a notebook computer from their office to a meeting and only actively use it for a few minutes. When returning to their office, they may reconnect the notebook computer to an auxiliary power source and it may initiate a recharge of its rechargeable batteries, even though they are almost fully charged. This causes unnecessary degradation of the rechargeable batteries.  
      Therefore, it would be desirable to provide a system and method for reducing the number of unnecessary recharge cycles or frequency of unnecessary recharge cycles for a rechargeable battery.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to a system and method for controlling the charge cycle of a rechargeable power source within portable electronic equipment to reduce the number of unnecessary recharge cycles for prolonging the useful life of the rechargeable power source.  
      In one aspect of the present invention, when auxiliary power is applied to the portable electronic equipment, the present charge level of its rechargeable batteries is determined. If the present charge level is relatively high, no charge cycle is initiated and the portable electronic equipment is powered by the auxiliary power source.  
      In another aspect of the present invention, when auxiliary power is applied to the portable electronic equipment, the present charge level of its rechargeable batteries is determined. If the present charge level is relatively high, no charge cycle is initiated, the portable electronic equipment is powered by the auxiliary power source and a trickle charge is provided to the rechargeable batteries to maintain their present charge level.  
      In another aspect of the present invention, when auxiliary power is applied to the portable electronic equipment, the present charge level of its rechargeable batteries is determined. If the present charge level is higher than a predetermined threshold, no charge cycle is initiated and the portable electronic equipment is powered by the auxiliary power source. The threshold may be provided as an absolute value or percentage of total capacity. Furthermore, in another embodiment, the threshold may be adjusted by the user.  
      In another aspect of the present invention, when auxiliary power is applied to the portable electronic equipment, the present charge level of its rechargeable batteries is determined. If the present charge level is higher than a predetermined threshold, no charge cycle is initiated, the portable electronic equipment is powered by the auxiliary power source and a trickle charge is provided to the rechargeable batteries to maintain their present charge level. The threshold may be provided as an absolute value or percentage of total capacity. Furthermore, in another embodiment, the threshold may be adjusted by the user.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description serve to explain the principles of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:  
       FIG. 1  is a block diagram of an illustrative system implementing the present invention.  
       FIG. 2  is a flow chart of the present invention.  
       FIG. 3  is a flow chart of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.  
      Referring generally now to  FIG. 1 , an illustrative electronic system according to the present invention is shown. The system shown is an example of an electronic device  100  having a rechargeable power source  160 , electronics that may be powered by the rechargeable power source  130 , a display  140  which may be an LCD, a charge control circuit  110 , and a power supply  170 . The power supply  170  may be internal to the electronic device or, perhaps, may be external such as provided with many portable electronic devices such as printers, notebook computers and the like. The power supply may or may not be connected to an external power source  180 , such as an AC outlet configured to provide AC line voltage.  
      Charge control circuit  110  monitors the status of the rechargeable power source  160 , or in this case a three-cell battery pack. When the electronic device is in use, charge control and regulation  110  provides regulated power to the electronics  130  and display  140  through connections  150 . In this embodiment, power supply  170  is shown disconnected from AC outlet  180 . In this mode, power for the system is provided by rechargeable power source  160  through charge control circuit  110 . When power supply  170  is connected to AC outlet  180 , it provides power to charge control circuit  110 . Recognizing this incoming power, charge control circuit  110  determines if rechargeable power source  160  should be recharged by determining the present charge of rechargeable power source  160  and comparing the present charge to threshold  120 . If the present charge is greater than threshold  120 , charge control circuit  110  does not initiate a charge cycle and may provide a trickle charge to rechargeable power source  160  to maintain its current charge level. If the present charge is less than threshold  120 , charge control circuit  110  initiates a charge cycle of rechargeable power source  160 . Once rechargeable power source  160  is fully charged, charge control circuit  110  may revert to a trickle charge to maintain a full charge of rechargeable power source  160 . Preferably, the value of the threshold  120  may be between approximately 75 percent and approximately 25 percent of the full charge capacity of the rechargeable power source  160 . In one embodiment of the invention, the value of the threshold  120  may be approximately 50 percent of the full charge capacity of the rechargeable power source  160 .  
      Referring now to  FIG. 2 , a flow chart of the present invention is shown. The status of external power is checked (step  210 ). If not connected to external power (determined at step  220 ), then step  210  is repeated. If connected to external power, the present charge capacity of the rechargeable power source is determined (step  230 ). This may be done by various methods known in the industry, including an actual measurement of the battery (perhaps by measuring its impedance) or by monitoring how much charge is put into the battery and how much power has been consumed by the electronic device. The present charge capacity is compared to a threshold value (step  240 ). This threshold value may be a preset amount or may be administered by the user. If the present charge capacity is less than the threshold (step  250 ), then a charge cycle is initiated (step  260 ). Otherwise, no charge cycle is initiated and the flow is complete.  
      Referring now to  FIG. 3 , a flow chart of the present invention is shown. The status of external power is checked (step  310 ), and if not connected to external power (step  320 ), then step  310  is repeated. If connected to external power, the present charge capacity of the rechargeable power source is determined (step  330 ). This may be done by various methods known in the industry, including an actual measurement of the battery (perhaps by measuring its impedance) or by monitoring how much charge is put into the battery and how much power has been consumed by the electronic device. The present charge capacity is compared to a threshold value (step  340 ). This threshold value may be a preset amount or may be administered by the user. If the present charge capacity is less than the threshold (step  350 ), then a charge cycle is executed (step  360 ). If the present charge capacity is higher than the threshold or the charge cycle is completed, a trickle charge of the rechargeable power source is initiated to maintain its present charge (step  370 ).  
      It is believed that the system and method of the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.