Patent Abstract:
A system and method are disclosed for charging battery packs. A battery pack connects to an external battery charger. A processor of the battery pack recognizes that the processor is connected the external battery charger. The external battery charger provides charging parameters to the battery pack. The processor sends charging parameters to the external battery in response to recognizing that the processor is connected to the external battery charger.

Full Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority of Japanese Patent Application No. 2006-029170, filed Feb. 7, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a system for charging battery cells used in portable electronic equipment and, in particular, to a charging system including a charger having a simplified structure for a battery pack including a processor. 
     2. Description of the Related Art 
     Lithium-ion batteries and nickel-hydride batteries, which have high energy densities, are often used in laptop personal computers (hereinafter referred to as laptop PCs), which are typical portable electronic equipment, because the laptop PCs require higher central processing unit (CPU) operating frequencies, longer operating times in mobile environments, and smaller sizes and lighter weights. To charge and discharge these batteries, recharge and discharge currents and voltages must be precisely controlled. Therefore, rather than conventional battery packs having only battery cells in a housing, battery systems called “smart batteries” are commonly used in which a microcomputer provided in the battery pack itself communicates with a laptop PC to exchange information while controlling charge and discharge. 
     Smart batteries are battery systems that are compliant with specifications called the Smart Battery System (SBS) specification proposed by Intel Corporation and Duracell Inc. in the United States. The first version, version 0.9, of the SBS specification was disclosed in 1995 and the latest version is Version 1.1. The SBS specification&#39;s main aim was to unify methods for controlling charge and discharge, measuring capacities, and communicating with laptop PCs, which had been being developed by laptop PC manufacturers on their own, to enable a battery pack itself to perform control of charge and discharge suitable to the chemical composition of the battery pack, thereby relieving the laptop PC designers of recharge/discharge control design work. Battery packs compliant with the SBS specification are referred to herein intelligent batteries. 
     An intelligent battery includes battery cells, which are the main unit to be charged and discharged, and electric circuitry including a CPU, a current measurement circuit, a voltage measurement circuit, and sensors contained on a substrate. In addition, the intelligent battery communicates with an embedded controller provided in a laptop PC through a data line. The intelligent battery can cooperate with the laptop PC to change a power consumption mode of the laptop PC in accordance with the remaining capacity of the battery or to shut off the laptop PC after displaying a warning on a display if remaining capacity becomes small or some abnormality occurs on the battery. 
     Two types of intelligent battery chargers, Level 2 and Level 3, are defined in the section “4.2 Smart Battery Charger Types” of the SBS specification “Smart Battery Charger Specification” Revision 1.1, released Dec. 11, 1998. In the case of the Level 2 battery charger, the intelligent battery is a master device and the battery charger is a slave device following the directions of the intelligent battery. The intelligent battery sends information about a current and voltage required for charging to the battery charger through a data line. The battery charger outputs a current and voltage based on the information. The Level 3 battery charger has a charger master operation mode in which the battery charger is the master device and the intelligent battery is the slave device following the battery charger. The Level 3 battery charger also has the battery master mode of the Level 2 battery charger. In the charger master mode, the battery charger sends an inquiry about a current and voltage required for charging to the intelligent battery and outputs a current and voltage according to a replay to it. 
     While a laptop PC equipped with a battery pack is being supplied with power from an alternating current (AC) power source, the battery pack is concurrently charged through a battery charger contained in the laptop PC. The laptop PC can then be used in a mobile environment. A user using a laptop PC in a mobile environment for a long time must charge spare battery packs beforehand. This requires many external battery chargers and places an extra cost burden on the user. 
       FIG. 7  shows a basic configuration of a conventional charging system.  FIG. 7(A)  shows a conventional battery pack  10 ′ attached to a laptop PC  100  being supplied with power from an AC power source. An AC adapter  123  is connected to the AC power source through an AC cord  125 , converts an AC voltage to a predetermined direct current (DC) voltage, and supplies power to the laptop PC  100  through a DC cable  127 . Power supplied to the laptop PC  100  is used by a system load of the laptop PC  100  and also used for charging the battery pack  10 ′.  FIG. 7(B)  shows the battery pack  10 ′ attached to and charged by an external battery charger  50 ′. The same AC adapter  123  that is attached to the laptop PC  100  is connected to the battery charger  50 ′. 
       FIG. 8  shows in detail the conventional battery pack  10 ′ shown in  FIG. 7(A)  attached to the laptop PC  100 . The battery pack  10 ′ is compliant with the SBS specifications. Provided in the battery pack  10 ′ are battery cells  11  and electronic components such as a microprocessor unit (MPU)  21 , a depletion field effect transistor (D-FET)  17 , a complementary field effect transistor (C-FET)  19 , a voltage regulator  23 , a thermistor  35 , a current measurement circuit  13 , and a voltage measurement circuit  15 . The battery pack  10 ′ is connected to the laptop PC  100  through five terminals: a positive terminal  37 , a C terminal  39 , a D terminal  41 , a T terminal  43 , and a negative terminal  45 . Power outputted from the battery cells  11  inside the battery pack  10 ′ is provided to the laptop PC  100  through the positive terminal  37  and the negative terminal  45 . The C terminal  39  and the D terminal  41  are connected to a clock terminal and a data terminal of the MPU  21 , respectively, and the T terminal is connected to the thermistor  35 . 
     The MPU  21  is an integrated circuit that operates on a constant voltage provided through the voltage regulator  23 . The MPU  21  may include a CPU of 8 to 16 bits or so, a RAM, a ROM, an analog input and output, a timer, and a digital input and output in one package. In addition, the MPU  21  may be capable of executing a program for controlling the battery pack  10 ′. The MPU  21  uses the current measurement circuit  13  and the voltage measurement circuit  15  to constantly monitor the current and voltage output from the battery  11  and controls the D-FET  17  for discharging of the battery  11  and the C-FET  19  for charging of the battery  11 . From the MPU  21 , a clock line and a data line lead to the embedded controller  115  of the laptop PC  100  through the C terminal  39  and D terminal  41 , respectively, so that the MPU  21  can communicate with the embedded controller  115 . 
     The resistance of the thermistor  35  changes in accordance with temperature. In one embodiment, the thermistor  35  is provided near the battery cells  11  and is connected to a voltage source Vcc through a pull-up resistance  121  of the laptop PC  100 , thereby functioning as a temperature measurement circuit. An output from the thermistor  35  is input into the embedded controller  115  through the T terminal  43 . The thermistor  35  is used for measuring the temperature of a battery. 
     The power management function of the laptop PC  100  is implemented by the embedded controller  115  together with a battery charger  117 , a control line  119 , a DC-DC converter  122 , and an AC adapter  123 . The embedded controller  115  is an integrated circuit that controls the power supply as well as many hardware components constituting the laptop PC  100 . The embedded controller  115  obtains information about the present current value and voltage value of the battery  11  through communication with the MPU  21  and, on the basis of the information, controls the battery charger  117  through the control line  119  to control charging of the battery pack  10 ′. 
     Power supplied from the AC adapter  123  and the battery pack  10 ′ is provided to components in the laptop PC through the DC-DC converter  122 . The embedded controller  155  is also connected onto an industry standard architecture (ISA) bus  113 , from which the embedded controller  155  is interconnected with and can communicate with a CPU  101 , a main memory  105 , and other hardware components constituting the laptop PC  100  through connections, including a peripheral component interconnect (PCI) bus  109 , a PCI-ISA bridge  111 , a CPU bridge  107 , and a front side (FS) bus  103 . Most of the other hardware components comprising the laptop PC  100  such as a display, a magnetic disk, an optical disk, and a keyboard are well known and therefore not shown in  FIG. 8 . 
       FIG. 9  shows in detail the battery pack  10 ′ shown in  FIG. 7(B)  attached to an external battery charger  50 ′. The internal configuration of the battery pack  10 ′ is the same as that of the battery pack  10 ′ connected to the laptop PC  100  shown in  FIG. 8 . The battery charger  50 ′ includes an MPU  116 , a switch (SW)  129 , a voltage regulator  51 , and a current regulator  53 . The MPU  116  plays a roll equivalent to the embedded controller  115  of the laptop PC  100  during charging the battery pack  10 ′. The MPU  116  obtains charging information such as the present current and voltage of the battery  11  through communication with the MPU  21  and, on the basis of the information, controls the SW  129 , the voltage regulator  51 , and the current regulator  53  to control charging in a manner similar to that in the laptop PC  100 . 
     The conventional external battery charger  50 ′ is capable of controlling charging of the battery pack  10 ′ in a manner similar to that used in the battery charger  117  incorporated in the laptop PC  100 . However, such an external battery charger  50 ′ is costly because it uses an MPU  116 . Therefore there is a demand for simplifying the structure of external battery chargers to reduce their costs. 
     SUMMARY OF THE INVENTION 
     From the foregoing discussion, there is a need for an apparatus, system, and method that charges a battery pack. Beneficially, such an apparatus, system, and method would simplify the structure of external battery chargers. 
     The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available battery charging methods. Accordingly, the present invention has been developed to provide a charging system and method for battery charging that overcome many or all of the above-discussed shortcomings in the art. 
     A charging system for a battery pack of the present invention is presented. In particular, the system, in one embodiment, includes an external battery charger and a battery pack. The external battery charger includes an identification circuit and a charging regulator. The external battery charger controls charging characteristics of the charging regulator in accordance with charging parameter values received from an external source. 
     The battery pack is attachable to an electronic apparatus having an identification circuit. In addition, the battery pack includes a battery cell and a processor capable of recognizing the identification circuit of the electronic apparatus and the identification circuit of the external battery charger and, upon recognizing the identification circuit of the external battery charger, sending the charging parameter values to the charging regulator. The charging system recognizes and sends the charging parameter values to the charging regulator to control charging of the battery pack, simplifying the structure of the external battery charger. 
     A method of the present invention is also presented for charging a battery pack. The method in the disclosed embodiments substantially includes the steps to carry out the functions presented above with respect to the operation of the described system. 
     A battery pack connects to an external battery charger. A processor of the battery pack recognizes that the processor is connected the external battery charger. The external battery charger provides charging parameters to the battery pack. The processor sends charging parameters to the external battery in response to recognizing that the processor is connected to the external battery charger. The method controls the controls the charging of the battery pack by the external battery charger with the charging parameters, simplifying the structure of the external battery charger. 
     References throughout this specification to features, advantages, or similar language do not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     The present invention charges battery packs with a simplified external battery charger structure. These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  shows a configuration of a charging system to which an embodiment of the present invention is applied; 
         FIG. 2  shows a state in which a battery pack to which the present embodiment is applied is attached to a laptop PC; 
         FIG. 3  shows a state in which the battery pack to which the present embodiment is applied is attached to an external battery charger; 
         FIG. 4  shows a method for determining and controlling a charging voltage value and charging current value of an external battery charger to which the present embodiment is applied; 
         FIG. 5  is a flowchart showing operation of a program executed by an MPU in a battery pack to which the embodiment is applied; 
         FIG. 6  shows a charging voltage and a charging current during charging of a battery pack to which the present embodiment is applied; 
         FIG. 7  shows a configuration of a conventional charging system; 
         FIG. 8  shows a conventional battery pack attached to a laptop PC; and 
         FIG. 9  shows the conventional battery pack attached to an external battery charger. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described below in detail with respect to an embodiment shown in the accompanying drawings.  FIG. 1  shows a configuration of a charging system to which an embodiment of the present invention can be applied.  FIG. 1(A)  shows a battery pack  10  attached to a laptop PC  100  being supplied with power from an AC power source. The laptop PC  100  operates on a DC voltage supplied from an AC adapter  123  and concurrently charges a laptop PC  10 . The AC adapter  123  converts an AC voltage supplied from a commercial power source through an AC cord  125  to a predetermined DC voltage and supplies the DC voltage to the laptop PC  100  through a DC cable  127 . The battery pack  10  is an intelligent battery compliant with the SBS specification.  FIG. 1(B)  shows the battery pack  10  attached to an external battery charger  50  being supplied with power from a commercial power source through the AC cord  125 . The battery charger  50  is integrated with an AC adapter and operates on AC power supplied directly through the AC cord  125 . 
       FIG. 2  shows in detail the battery pack  10  shown in  FIG. 1  (A) attached to a laptop PC  100 . The laptop PC  100  is the same as the conventional laptop PC shown in  FIG. 8  and therefore the description thereof will be omitted. The battery pack  10  is similar to the conventional battery pack  10 ′ shown in  FIG. 8  and therefore only features of the present invention will be described. 
     The battery pack  10  includes a first selector switch (SW 1 )  27 , a second selector switch (SW 2 )  29 , a voltage setting section (Vset)  31 , and a current setting section (Iset)  33  in addition to the components of the conventional battery pack  10 ′. The circuitry has been modified so that a voltage of the thermistor  35  is input into an analog input A/D # 3  of an MPU  21 . The MPU  21 , provided inside the battery pack  10 , is capable of operating the first selector switch (SW 1 )  27  and the second selector switch (SW 2 )  29 . The first selector switch (SW 1 )  27  couples one of an output of CLOCK terminal of the MPU  21  and an output of the voltage setting section (Vset)  31  to the C terminal  39 . The second selector switch (SW 2 )  29  couples one of an output of DATA terminal of the MPU  21  and an output of the current setting section (Iset)  33  to the D terminal  41 . The output of the voltage setting section (Vset)  31  may be coupled to the D terminal  41  and the output of the current setting section (Iset)  33  may be coupled to the C terminal  39 . The voltage setting section (Vset)  31  and the current setting section (Iset)  33  will be described later. 
     When the battery pack  10  is connected to the laptop PC  100 , the MPU  21  operates the first selector switch (SW 1 )  27  and the second selector switch (SW 2 )  29  to connect the outputs of the CLOCK terminal and DATA terminal of the MPU  21  to the C terminal  39  and D terminal  41 , respectively. Consequently, a clock line and a data line are connected from the MPU  21  to the embedded controller  115  of the laptop PC  100  through the C terminal  39  and the D terminal  41 , respectively to enable communication between the MPU  21  and the embedded controller  115 . The battery pack  10  identifies that either the laptop PC  100  or the external barter charger  50  the battery pack  10  has been connected as will be described hereafter. 
       FIG. 3  shows in detail the battery pack  10  shown in  FIG. 1(B)  attached to the external battery charger  50 . The internal configuration of the battery pack  10  is the same as that of the battery pack connected to the laptop PC  100  shown in  FIG. 2 . The external battery charger  50  includes a voltage regulator  51 , a current regulator  53 , a transformer  57 , and a pull-up resistance  121 ′ connected to a thermistor  35  through the T terminal  43 . The external battery charger  50  according to the present embodiment does not have an MPU and switches required by conventional external battery chargers. Furthermore, the external battery charger  50  according to the present embodiment includes the function of an AC adapter, which in the past has been separately provided for conventional external battery chargers. The external battery charger  50  of the present embodiment is capable of converting an AC voltage supplied from an AC power supply through the AC cord  125  to a DC voltage through use of the transformer  57 . In addition, the external battery charger  50  may adjust a voltage value and a charging current value using the voltage regulator  51  and the current regulator  53 . The pull-up resistance  121 ′ is connected to a voltage source Vcc having a voltage value equal to that of the laptop PC  100  but has a resistance different from that of the pull-up resistance  121  of the laptop PC  100 . 
     The parameters required for controlling charging of the battery pack  10  in a constant voltage constant current control (CVCC) mode are a charging voltage value and a charging current value. The type and physical characteristics of the battery cell  11  to be charged uniquely determine the charging voltage and current values. The voltage setting section (Vset)  31  generates a signal that provides a charge voltage value for charging the battery pack  10  to the external battery charger  50 . Similarly, the current setting section (Iset)  33  generates a signal that provides a charging current value for charging the battery pack  10  to the external battery charger  50 . 
     When the battery pack  10  is connected to the external battery charger  50 , the MPU  21  operates the first selector switch (SW 1 )  27  and the second selector switch (SW 2 )  29  to connect the output of the voltage setting section (Vset)  31  and the output of the current setting section (Iset)  33  to the C terminal  39  and the D terminal  41 , respectively. The voltage regulator  51  and the current regulator  53  receive the signals indicating the charging voltage value and the charging current value set by the voltage setting section (Vset)  31  and the current setting section (Iset)  33  through the C terminal  39  and the D terminal  41 , and adjust the charging voltage and current values to the charging voltage value and the charging current value to perform charging. A specific method for determining the charging voltage and current values will be described later. 
     The MPU  21  determines whether the charging has been completed on the basis of a charging current and voltage measured at a current measurement circuit  13  and a voltage measurement circuit  15 , respectively. If the MPU  21  determines that the charging has been completed, the MPU  21  turns off a D-FET  17  and a C-FET  19  to stop the charging of the battery pack  10 . The external battery charger  50  has a simplified structure and does not include a switch that turns off its output voltage. 
     A voltage value of the thermistor  35  is input in the analog input A/D # 3  of the MPU  21 . The thermistor  35  is connected to a voltage source Vcc through a pull-up resistance  121 ′ of the external battery charger  50  through the T terminal  43 . Since the pull-up resistance  121 ′ has a sufficiently high impedance, the voltage source Vcc does not influence temperature measurement by the embedded controller when the battery pack  10  is connected to the laptop PC  100  while the thermistor  35  is connected to the pull-up resistance  121 ′. The resistance values of the pull-up resistance  121 ′ of the external battery charger  50  and the pull-up resistance  121  of the laptop PC  100  are different, so that the voltage value input into the analog input A/D # 3  of the MPU  21  varies depending on whether the battery pack  10  is connected to the external battery charger  50  or the laptop PC  100 . The difference in the voltage value input into the A/D # 3  identifies which of the laptop PC  100  and the external battery charger  50  the battery pack  10  is connected to. Furthermore, the voltage value input in the A/D # 3  readily identifies a state in which the battery pack  10  is connected to neither the external battery charger  50  nor the laptop PC  100 . In that state, input and output of power are turned off by the D-FET  17  and the C-FET  19  mentioned above. 
     The MPU  21  identifies whether the battery pack  10  is connected to the external battery charger  50  or the laptop PC  100  from the voltage value input into the A/D # 3 . Therefore, various embodiments can be contemplated in addition to the example described above in which the external battery charger  50  and the laptop PC  100  differ in resistance values of pull-up resistance and/or voltage value of the voltage source Vcc. For example, the pull-up resistance values of the external battery charger  50  and the laptop PC  100  may be equal and the voltage values of the voltage sources Vcc may be different. In another example, both of the resistance values of the pull-up resistances and the voltage values of the voltage sources Vcc may differ between the external battery charger  50  and the laptop PC  100 . 
     The configuration of the battery pack  10  described above can be implemented by adding a few elements to a conventional battery pack  10 ′ and making modifications to firmware inside the MPU  21  to cause it to perform operation as shown in  FIG. 5 , which will be described later. Thus, implementation of the battery pack  10  requires only minor modifications. Since the MPU  21  can also be omitted from the external battery charger  50 , the external battery charger  50  can be significantly simplified in structure and can be manufactured at a low cost accordingly. Terminals for connecting an intelligent battery to a laptop PC  100  can be used to connect the battery pack  10  to the external battery charger  50 . Therefore, no extra terminals need to be provided in the battery pack  10  and no modifications to software and hardware of the laptop PC  100  are required. 
     It should be noted that  FIGS. 1 to 3  schematically show principle hardware configuration and connections for the purpose of illustrating the present embodiment. While many other electric circuits and devices are used in addition to these components to implement the battery pack  10 , external battery charger  50 , and laptop PC  100 , they are well known to those skilled in the art and therefore are not described herein. It will be understood that multiple blocks shown in  FIGS. 1 to 3  may be integrated into a single integrated circuit or a single block may be separated into multiple integrated circuits. Such implementations also fall within the scope of the present invention as is well known to those skilled in the art. 
       FIG. 4  shows determining and controlling the charging voltage and current values in the external battery charger  50  to which the present embodiment is applied. As described above, the external battery charger  50  includes the function of an AC adapter and operates on an AC voltage directly supplied through the AC cord  125 . The AC voltage inputted through the AC cord  125  is first full-wave rectified by a rectifier bridge diode  71  on the primary side, and then smoothed by a capacitor  69 , and provided to a primary-side coil of a transformer  57 . Also provided on the primary side are a switching transistor  67  which makes switching operation on the voltage having been rectified and smoothed, a pulse width modulation (PWM) IC  65  which controls switching of the switching transistor  67  and provide a predetermined operation frequency, and a photo-transistor (TR 1 )  63  which receives an output feedback from the secondary-side photodiode (PD 1 )  61  and controls the periodicity of PWM in accordance with the level of the output voltage. 
     On the secondary side, a photodiode (PD 1 )  61  for feeding outputs from the voltage regulator  51  and the current regulator  53  back to the primary side is provided in addition to the voltage regulator  51  and the current regulator  53 . Since the primary circuitry must be electrically separated from the secondary circuitry for safety reasons, a photocoupler is used between the photodiode (PD 1 )  61  on the secondary side and the phototransistor (TR 1 )  63  on the primary side. 
     A resistance R 13   31  provided inside the battery pack  10  functions as a voltage setting section (Vset)  31  that sets a charging voltage value Vchg. While the battery pack  10  is connected to the external battery charger  50 , a first selector switch (SW 1 )  27  connects the resistance R 13   31  to a C terminal  39 . The difference between the charging voltage value Vchg and an actual charging voltage provided from the external battery charger  50  to the battery pack  10  is output from an operational amplifier AMP  11  in a voltage regulator  51  in the external battery charger  50  as the difference between a second reference voltage Vref 2  and the input voltage. Here, equation (1) given below holds in the voltage regulator  51 , where R 11 , R 12 , and R 13  are resistances, Vchg is the charging voltage vlue, and Vref 2  is the second reference voltage. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     From the equation, the following equation (2) can be derived and the charging voltage value Vchg can be established according to equation (2). 
     
       
         
           
             
               
                 
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     Resistance R 3  provided in the battery pack  10  functions as a current setting section (Iset)  33  that sets a charging current value Ichg. When the battery pack  10  is connected to the external battery charger  50 , a second selector switch (SW 2 )  29  connects R 3  to a D terminal  41 . The difference between the set charging current value Ichg and an actual charging current value provided from the external battery charger  50  to the battery pack  10  is output from an operational amplifier AMP 1  in a current regulator  53  in the external battery charger  50  as the difference between a reference voltage Vref 1  and the input voltage. Here, equation (3) given below holds in the current regulator  53 , where Rs, R 1 , R 2 , and R 3  are resistances, Ichg is the charging current value, and Vref 1  is the first reference voltage. 
     
       
         
           
             
               
                 
                   
                     
                       
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                       Rs 
                     
                   
                   = 
                   Ichg 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     From this equation, equation (4) given below can be derived and the charging current value Ichg can be established. 
     
       
         
           
             
               
                 
                   Ichg 
                   = 
                   
                     
                       ( 
                       
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         
                           
                             
                               R 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                               * 
                               R 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                             
                               R 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               3 
                             
                           
                           + 
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                       
                       ) 
                     
                     * 
                     
                       
                         Vref 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       Rs 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     As has been described above, the voltage setting section (Vset)  31  and the current setting section (Iset)  33  in the battery pack  10  in practice can set a charging voltage value and a charging current value according to equations (2) and (4) simply by setting resistance values R 3  and R 13 . Therefore, the battery pack  10  can be implemented at an extremely low cost. 
     If an excess voltage or current is generated, an output equivalent to the excess current outputted from the AMP 1  and an output equivalent to the excess voltage outputted from the AMP 11  are combined and output to the photodiode (PD 1 )  61 . The output from the photodiode (PD 1 )  61  is fed back to the power width modulator IC  65  on the primary side through the phototransistor (TR 1 )  63  which forms a photocoupler. When feedback equivalent to an excess voltage or current is provided to the phototransistor (TR 1 )  63 , the pulse width modulator IC  65  reduces the pulse width by means of the switching transistor  67  to reduce the period during which the switching transistor  67  is in the on state. Thus, the charging voltage value and the charging current value are controlled to a constant level. Methods for controlling the voltage value and current value by using pulse width modulation in a switching-regulator-based power supply unit used for an AC adapter for laptop PCs are well known to those of skill in the art. The external battery charger  50  according to the present embodiment can be readily implemented by adding a voltage regulator  51  and a current regulator  53  to the power supply unit so that outputs from the AMP 1  and AMP 11  are inputted into the photodiode (PD 1 )  61 . 
       FIG. 5  is a flowchart of an operation of a program executed by the MPU  21  when the battery pack  10  described above is connected to the laptop PC  100  or the external battery charger  50 . The program is provided as firmware stored in the MPU  21 . It should be noted that the D-FET  17  and C-FET  19  are in the off state when the program shown in  FIG. 5  is activated because the battery pack  10  turns off the D-FET  17  and C-FET  19  when the battery pack  10  is connected to neither the external battery charger  50  nor the laptop PC  100 . 
     First, when a voltage is input into the analog input A/D # 3  of the MPU  21 , it is determined that the battery pack  10  is likely to have been connected to the laptop PC  100  or the external battery charger  50  and the program is activated (block  301 ). Then, determination is made as to whether the battery pack  10  is connected to the laptop PC  100  or the external battery charger  50  (blocks  303  through  305 ). More specifically, if the voltage input into the analog input A/D # 3  indicates the resistance value of the pull-up resistance  121 ′ of the external battery charger  50 , it is determined that the battery pack  10  is connected to the external battery charter  50 . On the other hand, if the input voltage indicates the resistance value of the pull-up resistance  121  of the laptop PC  100 , it is determined that the battery pack  10  is connected to the laptop PC  100 . If the input voltage indicates neither of these values, it is determined that the battery pack  10  is connected to neither of the laptop PC  100  nor the external battery charger  50  and the process will end (block  339 ). 
     If it is determined that the battery pack  10  is connected to the laptop PC  100 , the first selector switch (SW 1 )  27  and the second selector switch (SW 2 )  29  are switched to connect the outputs of the CLOCK terminal and DATA terminal of the MPU  21  to the C terminal  39  and D terminal  41 , respectively (block  311 ). Then, the D-FET  17  and the C-FET  19  are turned on (block  313 ). As a result, communication between the MPU  21  and the embedded controller  115  is started (block  315 ). The battery pack  10  starts functioning as an intelligent battery (block  317 ) and then the operation of the program will end (block  339 ). The present current value and voltage value of the battery pack  10  are sent to the laptop PC  100  through communication between the MPU  21  and the embedded controller  115 . If the battery pack  10  needs to be charged, charging power is provided from a charger  117  on the laptop PC  100 . 
     On the other hand, if it is determined that the battery pack  10  is connected to the external battery charger  50 , determination is made first as to whether the battery pack  10  needs to be charged (blocks  321  and  323 ) on the basis of a current value and voltage value measured by a current measurement circuit  13  and a voltage measurement circuit  15 . If the battery pack  10  does not need to be charged, the operation of the program will end (block  339 ). If the battery pack  10  needs to be charged, the first selector switch (SW 1 )  27  and the second selector switch (SW 2 )  29  are switched to connect the outputs of the voltage setting section (Vset)  31  and the current setting section (Iset)  33  to the C terminal  39  and the D terminal  41 , respectively, (block  325 ) to set a charging voltage value and current value to be outputted. After the charging voltage and current values are set, the D-FET  17  and the C-FET  19  are turned on (block  327 ) to provide the set charging voltage and current values to the battery pack  10 , thereby staring charging of the battery pack  10  (block  329 ). On completion of the charging (block  331 ), the D-FET  17  and the C-FET  19  are turned off, thereby ending the charging (block  333 ), and the operation of the program will end (block  339 ). 
       FIG. 6  shows a charging voltage and a charging current during charging of the battery pack  10 .  FIG. 6(A)  is a block diagram of the battery pack  10  viewed from near the battery cells  11  during charging and shows where a voltage Vout and current lout are measured;  FIG. 6(B)  shows changes in the voltage Vout and the current Iout output from the external battery charger  50 . If the battery cells  11  are lithium-ion cells, charging is performed in a constant voltage/constant current control mode. Hereafter, the charging voltage value set by the voltage setting section (Vset)  31  is denoted by Vchg, the charging current value set by the current setting section (Iset)  33  is denoted by Ichg, the voltage across the cell is denoted by Vcell, and the DC resistance of the cell (excluding the DC resistance of the battery pack  10 ) is denoted by Rpk. The constant current period  201  is a time period during which charging is performed at a constant current value. As represented by curve  209  in  FIG. 6(B) , the current lout is kept at the set current value Ichg during the constant current period  201 . The voltages Vout and Vcell gradually increase as represented by curves  205  and  207 . When the voltage Vcell reaches a value at which Equation (5) is satisfied, the voltage Vout becomes equal to the set voltage value Vchg and a constant voltage period  203  is entered.
   Vchg=IchgRpk+V cell   (5) 
     In the constant voltage period  203 , the voltage Vout remains at the set voltage value Vchg, the voltage Vcell gradually approaches Vchg, and the current lout gradually decreases. The voltage Vout becomes approximately equal to Vcell. When the current lout becomes equal to the set charging end current  211 , the charging of the battery pack  10  ends. The MPU  21  constantly monitors the values of Vcell and lout through the voltage measurement circuit  15  and the current measurement circuit  17  provided inside the battery pack  10 . When a charging end state is reached, the MPU  21  turns off the D-FET  17  and the C-FET  19 , thereby completing the charging. 
     The voltage value and current value suitable for charging a battery pack  10  vary depending on the structure and physical characteristics of the battery pack  10 . Conventionally, the MPU  21  of a battery pack  10  has indicated a charging voltage value and charging current value to be set to an external battery charger  50  through communication with the MPU of the external battery charger  50 . According to the present invention, internal resistance values in the voltage setting section and the current setting section are also set in the external battery charger  50  having an inexpensive and simple structure without an MPU, whereby each individual battery pack  10  can hold information about a voltage value and a current value suitable for charging of the battery pack  10 . This eliminates the need for providing different external battery chargers  50  for different types of battery packs  10  but instead a single external battery charger  50  can be used for charging many types of battery packs  10 . 
     Furthermore, according to the present embodiment, a charging voltage value and a charging current value can be readily set by using only internal resistance values in the voltage setting section and the current setting section. Therefore, if a single battery pack  10  requires multiple sets of charging voltage and charging current values, the charging voltage and charging current values can be set simply by selecting values from among multiple resistance values provided inside the voltage setting section and the current setting section by using selector switches. Since the numbers of switches and resistances in the battery pack  10  are only slightly increased, the manufacturing cost of the battery pack  10  is not significantly increased and an external battery charger  50  in the same embodiment described above may be used. 
     In an alternative embodiment, as a voltage setting section and a current setting section, voltages equivalent to a charging voltage and current values instead of resistance values may be directly provided from the analog output of the MPU  21  to a voltage regulator  51  and a current regulator  53 . The alternative embodiment also can be implemented by making slight modifications to firmware in the MPU  21  and switches in the battery pack  10 . 
     While the present invention has been described with respect to the specific embodiment shown in the drawings, the present invention is not limited to the embodiment shown in the drawings. It will be understood that any equivalent configurations may be used as long as they provide the effects of the present invention. 
     The present invention can be applied to a charging system including a battery pack  10  having an internal processor therein and an external battery charger  50 . In addition, the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Technology Classification (CPC): 7