Abstract:
A charging system has a battery pack and a charging device. The battery pack has a battery cell and a plurality of identifiers that identify a configuration of the battery cell. The charging device has a charging unit, a signal transmission unit, a reading unit, and a control unit. The charging unit charges the battery pack. The signal transmission unit transmits a first signal and a second signal to the battery pack separately to read the plurality of identifiers when the battery pack is attached to the charging unit. The reading unit reads the plurality of identifiers according to the first and second signals to determine the configuration of the battery cell. The control unit controls the charging unit according to the configuration of the battery cell.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from Japanese Patent Application No. 2008-016958 filed Jan. 28, 2008. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a battery pack comprising a secondary battery such as a lithium ion secondary battery, a charging device for charging the battery pack, and a charging system including the charging device for charging the battery pack. 
       BACKGROUND 
       [0003]    In general, a cordless electric tool uses a secondary battery pack that is rechargeable with a charging device as a power supply. A lithium ion (Li-ion) battery cell is commonly used to form the secondary battery pack. A charging device for a Li-ion type battery pack generally charges the battery pack with a constant charging current and at a constant charging voltage. In particular, in order to avoid reverse charging for each battery cell, the charging device charges the battery pack with the constant charging current until the battery voltage reaches a predetermined value, for example, 4.2 V/cell, and then charges at the constant charging voltage until the current passing through the battery pack reduces under a predetermined value due to full charging. 
         [0004]    There are two types of battery pack to be charged by the charging device: a first type of battery pack and a second type of battery pack. The first type of battery pack is a 4S1P type of battery pack having a nominal voltage of 14.4 V, in which four battery cells are connected in series. The second type of battery pack is a 4S2P type of battery pack having a nominal voltage of 14.4 V, in which a pair of battery cells is connected in parallel and four pairs of parallel-connected battery cells are connected in series. Each of the battery packs generally has an identifying resistor identifying the configuration of the battery cells in the battery pack. 
         [0005]    If one charging device selectively charges the above two different types of battery packs and flows the same amount of charging current through each battery pack, the amount of current passing through each cell of the 4S1P type is twice as much as the amount of current passing through each cell of the 4S2P type. This phenomenon may result in shortening the lifespan of the 4S1P type, compared with the lifespan of the 4S2P type. 
         [0006]    The charging device has a unit for detecting the identifying resistor of the battery pack to determine the type thereof. When the first battery pack having a nominal voltage of 14.4 V (which includes four battery cells connected in series) has a resister having a resistance of a, and the second battery pack having a nominal voltage of 18 V (which includes five battery cells connected in series) includes a resister having a resistance of b, a microcomputer of the charging device detects the divided voltage of a reference voltage by the resistor of a or b and the internal resistor w of the charging device, and then determines which the first or second battery pack is connected with the charging device. 
         [0007]    As described above, each battery pack has an identifying resistor having its own resistance. However, if the charging device erroneously determines the resistance of the identifying resistor, the charging device may feed an improper current flow to the battery pack, which may adversely affecting the lifetime of the battery pack. 
         [0008]    An object of the invention is to provide a charging system in which a charging device suitably feeds a charging current to a battery pack, depending on the type of the battery pack. 
       SUMMARY 
       [0009]    The present invention provides a battery pack having a battery cell, and one or more identifiers that identify a configuration of the battery cell. 
         [0010]    The present invention further provides a charging device having a charging unit, a signal transmission unit, a reading unit, and a control unit. The charging unit charges a battery pack. The signal transmission unit transmits a first signal and a second signal to the battery pack separately to read a plurality of identifiers included in the battery pack when the battery pack is attached to the charging unit. The reading unit reads the plurality of identifiers of the battery pack according to the first and second signals to determine the configuration of the battery cell included in the battery pack. The control unit controls the charging unit according to the configuration of the battery cell. 
         [0011]    Further, the present invention is applicable to a charging system including the battery pack and the charging device according to the present invention. In this case, the charging system exhibits the similar advantages to those of the battery pack and the charging device of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a circuit diagram of a charging device according to the present invention; 
           [0014]      FIG. 2  shows a flowchart illustrating a process for charging a battery pack with the charging device shown in  FIG. 1 ; 
           [0015]      FIGS. 3A to 3D  show divided voltages inputted to microcomputer, depending on configuration of battery pack, to determine the configuration of battery pack; and 
           [0016]      FIG. 4  is a circuit diagram of a charging device for charging a battery pack according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The next description will explain a charging system  200  according to an embodiment of the present invention, referring to  FIGS. 1 and 2 .  FIG. 1  shows a circuit diagram of the charging system  200  including a charging device  1  for charging a battery pack  2  with power supplied from an alternating-current power supply P. 
         [0018]    The charging device  1  charges any one of different types of battery packs  2 . In this embodiment, the battery packs  2  includes a first type of battery pack  2  and a second type of battery pack  2 , which has a different configuration of battery cells  2   a . The configuration of battery cells  2   a  means the number of series-connected battery cells and a connection manner of the battery cells in the battery pack: series-connection or parallel-connection, how many cells are connected in series, and how many cells are connected in parallel. Each of the first and second types of battery cells  2   a  includes a single battery cell  2   a  or a plurality of battery cells  2   a  and has a positive terminal and a negative terminal. The battery cells  2   a  is made from a lithium ion (Li-ion) secondary cell. The battery pack  2  further includes a protection IC  2   b  that monitors a charging voltage applied across each battery cell  2   a  and produces a signal on detecting over-charge or over-discharge of the battery cell  2   a.    
         [0019]    The first type of battery pack includes a single battery cell  2   a  or a plurality of battery cells  2   a  connected in series, so called, a 1P type of battery pack. One example is a 4S1P battery pack having a nominal voltage of 14.4V. The 4S1P battery pack includes four battery cells  2   a  connected in series. 
         [0020]    The second type of battery pack includes a single battery unit or a plurality of battery units connected in F series, each battery unit including two battery cells  2   a  connected in parallel. The second type of battery pack is so called a 2P type of battery pack. One example is a 4S2P battery pack having has a nominal voltage of 14.4 V and having eight battery cells  2   a , in which two battery cells  2   a  are connected in parallel to form one battery unit and four battery unit are connected in series. The second type of battery pack  2  may have more than two battery cells  2   a  connected in parallel in each battery unit. As described above, the second type of battery pack includes a plural-P type of battery pack (plural being an integer more than 1). For example, a 4S3P battery pack has twelve battery cells  2   a  in which three battery cells  2   a  are connected in parallel to form one battery unit and four battery units are connected in series. 
         [0021]    The battery pack  2  further includes a battery type identifier  7 , a thermosensor  8 , and a switching portion  120 . The battery type identifier  7  represents a configuration of the battery cells  2   a  in the battery pack  2 . In particular, the battery type identifier  7  represents the number of battery cells  2   a  and their connecting configuration such as series-connection and/or parallel connection in the battery pack  2 . The battery type identifier  7  includes a first battery identifying resistor  7   a  and a second battery identifying resistor  7   b  connected in series. The first battery identifying resistor  7   a  identifies the number of battery cells  2   a  connected in series and is used for the charging device  1  to determine how many battery cells  2   a  are connected in series in the battery pack  2 . The second battery identifying resistor  7   b  identifies the configuration of battery cells  2   a . And the second battery identifying resistor  7   b  is used to determine the configuration of the battery cells  2   a , simple series connection or parallel connection, when the second resister  7   b  is operationally connected with the first resister  7   a  in series. Specifically, the second battery identifying resistor  7   b  identifies the configuration of the battery pack  2  such as simple series-connection or parallel-connection. In this embodiment, the simple series connection means a plurality of battery cells  2   a  connected in series without including any parallel connection of battery cells  2   a.    
         [0022]    The thermosensor  8  is a thermistor provided close to or on the battery cell  2   a  to detect a temperature in the battery pack  2 . Resistors  2   c ,  2   d ,  2   e ,  2   f , and FETs  2   g ,  2   h  are provided around to be associated with the themosensor  8 . 
         [0023]    The switching portion  120  includes a FET  121  and resistors  122  and  123 , and is connected to a node between the first and second battery identifying resistors  7   a  and  7   b . The FET  121  is controlled by a control signal supplied from the charging device  1 . During a normal operation, the switching portion  120  receives an input voltage Vcc from the charging device  1  and the protection IC  2   b  does not generate any signal, so that the input voltage Vcc is applied to gates of the FETs  2   g  and  2   h  to turn on the FET  2   h.    
         [0024]    On the other hand, if over-discharge from the battery cell  2   a  happens, the protection IC  2   b  generates a LOW signal to turn off the FET  2   h  and turn on the FET  2   f . Accordingly, the battery pack  2  outputs the voltage Vcc to the charging device  1  instead of the voltage related to the temperature of the battery pack  2  and informs the charging device  1  that the over-discharge of the battery cell  2   a  occurs. 
         [0025]    The charging device  1  is provided with a current detection unit  3 , a charging control signal transmission unit  4 , a charging current signal transmission unit  5 , a rectification smoothing circuit  6 , a battery type determination resistor  9 , a rectification smoothing circuit  10 , a switching circuit  20 , a rectification smoothing circuit  30 , a power supply  40 , a microcomputer  50 , a charging current control circuit  60 , a charging current setting unit  70 , a battery temperature detection unit  80 , a battery voltage detection unit  90 , a charging voltage control unit  100 , a display unit  130 , and a switching unit  140 . 
         [0026]    The current detection unit  3  is a resistor, and detects a voltage applied across the resistor in order to obtain a charging current flowing through the battery pack  2 . 
         [0027]    The rectification smoothing circuit  10  includes a full-wave rectifier circuit  11  and a smoothing capacitor  12 . The full-wave rectifier circuit  11  rectifies the alternating-current supplied from the alternating-current power supply P, and the smoothing capacitor  12  smoothes the direct-current outputted from the full-wave rectifier circuit  11 . 
         [0028]    The switching circuit  20  includes a high-frequency transformer  21  having a primary winding and a secondary winding, a MOSFET (switching element)  22  connected with the primary winding in series, and a PWM control IC (switching control IC)  23 . 
         [0029]    A driving power for the PWM control IC  23  is supplied from the rectification smoothing circuit (direct current power source)  6 . The rectification smoothing circuit  6  includes a transformer  6   a , a rectifier diode  6   b , and a smoothing capacitor  6 c, and passes the power from the power supply  40  to the PWM control IC  23 . The PWM control IC  23  receives a charging voltage control signal and a charging current control signal through the charging current signal transmission unit  5 , which is a photocoupler, from the charging current control circuit  60 . The PWM control IC  23  receives a start signal and a stop signal for controlling start and stop of charging the battery pack  2  through the charging control signal transmission unit  4 , which is a photocoupler, from the microcomputer  50 . The PWM control IC  23  changes the drive pulse width applied to the gate of the MOSFET  22  in order to adjust an output voltage outputted to the rectification smoothing circuit  30  and a charging current passing through the battery pack  2 . 
         [0030]    The rectification smoothing circuit  30  includes a diode  31  connected with the secondary winding of the transformer  21 , a smoothing capacitor  32 , and a discharging resistor  33 . The diode  31  rectifies the alternating-current supplied from the switching circuit  20 , and the smoothing capacitor  32  smoothes the direct-current outputted from the diode  31 . 
         [0031]    The determination resistor  9  divides a reference voltage (stabilized direct voltage) Vcc together with the identifier  7 . The divided voltage is outputted as cell configuration information indicating the number of the battery cells  2   a  and their configuration in the battery pack  2 . 
         [0032]    The power supply  40  includes transformers  41   a  to  41   c , a switching element  42 , a control element  43 , a rectifier diode  44 , a three-terminal regulator  46 , a smoothing capacitor  45  connected to an input terminal of the regulator  46 , a smoothing capacitor  47  connected to an output terminal of the regulator  46 , and the reset IC  48 , and supplies power to the microcomputer  50  and the rectification smoothing circuit  6 . The reset IC  48  outputs a reset signal to the microcomputer  50  through the reset port  53  when the commercial power source P supplies power to the charging device  1 . 
         [0033]    The microcomputer  50  includes output ports  51   a  and  51   b , an A/D input port  52 , and the reset port  53 . The microcomputer  50  further includes a central processing unit (CPU), a read-only-memory (ROM) for storing control programs for the CPU and data associated with the types of battery packs  2 , a random-access memory (RAM) used for a working area for the CPU and a temporary storage area for the data, and a timer. The cell configuration information outputted from the determination resistor  9 , the battery temperature information outputted from the battery temperature detection unit  80 , the battery voltage information outputted from the battery voltage detection unit  90 , and the voltage detected by the current detection unit  3  are inputted into the A/D port  52 . Accordingly, the microcomputer  50  determines the battery temperature and the battery voltage. The microcomputer  50  generates control signals to the power supply  40  and the charging current control circuit  60 , and outputs control signals to the charging control signal transmission unit  4  and the display unit  130 , and a charging state signal from the output port  51   a.    
         [0034]    the microcomputer  50  determinates the configuration and the number of the series-connected cells of the battery pack  2  based on the cell configuration information, and outputs a charging voltage control signal corresponding to the number of the series-connected cells from the output port  51   b  to the charging voltage control unit  100 . The microcomputer  50  outputs a charging current control signal based on the cell configuration information to the charging current setting unit  70 . The microcomputer  50  outputs a control signal to turn on/off a FET  141  in the switching unit  140 . The reset port  53  receives a reset signal from the reset IC  48 . 
         [0035]    The charging current control circuit  60  includes an operational amplifier circuit having operational amplifiers (op-amps)  61  and  65 , input resistors  62  and  64  and feedback resistors  63  and  66  for the op-amps  61  and  65 , a diode  68 , and current limiting resistor  67 . An inverting terminal of the op-amp  61  is connected to the current detection unit  3 . A non-inverting terminal of the op-amp  65  is connected to the charging current setting unit  70 . An output terminal of the charging current control circuit  60  is connected to the PWM control IC  23  through the charging current signal transmission unit  5 . The charging current control circuit  60  outputs the current control signal based on both the charging current (the voltage) detected by the current detection unit  3  and the reference value outputted from the charging current setting unit  70 . An output terminal of the op-amp  61  is connected to the A/D converter  52  in order to monitor the charging current, so that the microcomputer  50  determines a reduction of the charging current when the battery pack  2  is fully charged. 
         [0036]    The charging current setting unit  70  sets an amount of charging current passing through the battery pack  2 , depending on the type of the battery pack  2 . The charging current setting unit  70  includes resistors  71  and  72  connected in series between the reference voltage Vcc and a ground. The charging current setting unit  70  further includes a resistor  73  which may be connected with the resistor  72  in parallel. The reference voltage Vcc is divided by the resistors  71  and  72 , and the divided voltage is outputted as a reference value for setting the charging current. The resistor  73  is connected with the with the resistor  72  in parallel, depending on the type of the battery pack  2 , so that the charging current setting unit  7  changes the amount of charging current. 
         [0037]    For example, if the microcomputer  50  generates no signal to control that only the resistor  72  is selected as being connected with the resistor  71  in series, the microcomputer  50  sets a first charging current I 1  passing through the battery pack  2 . If the microcomputer  50  generates a LOW signal to control that the resistor  73  is selected as being connected to the resistor  72  in parallel and the resistor  71  is connected with the parallel-connected resistors  72  and  73 , the microcomputer  50  sets a second charging current I 2  passing through the battery pack  2 . In this case, the microcomputer  50  sets the amount of the first charging current more than the amount of the second charging current. 
         [0038]    In the charging current control circuit  60 , the resistors  62  and  63  and the op-amp  61  invert and amplify the voltage across the current detection unit  3 . The op-amp  65  amplifies the difference between the output of the op-amp  61  and the setting voltage corresponding to the charging current value set by charging current setting unit  70 . The output of the charging current control circuit  60  is supplied to the PWM control IC  23  through the charging current signal transmission unit  5  to control the switching operation of the MOSFET  22 . In other words, the current detection unit  3 , the charging current control circuit  60 , the charging current signal transmission unit  5 , the switching circuit  20 , and the rectification smoothing circuit  30  adjust the actual charging current passing through the battery pack  2  to the charging current set by the charging current setting unit  70 . 
         [0039]    The battery temperature detection unit  80  includes resistors  81  and  82  connected in series between the reference voltage Vcc and the ground (voltage divider circuit). The reference voltage Vcc is divided by the resistor  81  and the combined resistance of the thermosensor  8  and the resistor  82  when the FET  2   h  is turned on. The divided voltage representing a temperature change in the resistance of the thermosensor  8  is outputted as battery temperature information to an A/D convertor  52  of the microcomputer  50 . 
         [0040]    The battery voltage detection unit  90  includes resistors  91  and  92 , and is connected with the positive terminal of the battery pack  2 . The battery voltage is divided by the resistors  91  and  92 , and the divided voltage is outputted as battery voltage information to the A/D convertor  52  of the microcomputer  50 . 
         [0041]    The charging voltage control unit  100  controls the charging voltage applied across the battery pack  2 , and includes resistors  101 ,  105 ,  106 ,  107 ,  108 , and  109 , a potentiometer  102 , a capacitor  104 , a shunt regulator  110 , a rectifying diode  111 , and a FET  112 . The charging voltage is determined in the manner that a divided voltage by the series resistance of the resistor  101  and the potentiometer  102 , and the resistor(s)  105  and/or  106 , the resistor  109  becomes equal to a reference voltage of the shunt regulator  110 . For example, the charging voltage defined by the series resistance of the resistor  101  and the potentiometer  102 , and the resistor  105  is used for charging the battery pack  2  having four battery cells connected in series. And, the charging voltage defined by the series resistance of the resistor  101  and the potentiometer  102 , and the parallel resistance of the resistors  105  and  106  is used for charging the battery pack  2  having five battery cells connected in series. In the latter case, the FET  112  is turned on. 
         [0042]    The display unit  130  indicates the charging state of the battery pack  2 , and includes an LED  131 , resistors  132  and  133 . The LED  131  includes a green diode G and a red diode R. When the charging state signal outputted from the output port  51   a  is inputted into the red diode R via the resistor  132 , the red diode R lights up with red color, and indicates that the battery pack  2  is prior to charging. When the charging state signal is inputted into the green diode G via the resistor  133 , the green diode G lights up with green color, and indicates that charging battery pack  2  is completed. Furthermore, when the charging state signal are inputted into both the green diode G via the resistor  133  and the red diode R via the resistor  132  concurrently, the LED  131  lights up with orange color, and indicates that the battery pack  2  is in a process for charging. In this embodiment, the LED  131  lights up with the red color before charging, with the orange color during charging, and with the green color after charging. 
         [0043]    The switching unit  140  includes the FET  141  and resisters  142 ,  143  to control the FET  121  in the battery pack  2 . The FET  141  is controlled by a control signal from the microcomputer  50 . When receiving a LOW signal from the microcomputer  50 , the FET  141  is turned on so that the reference voltage Vcc is applied to the gate of the FET  121  in the battery pack  2 . When the FET  121  is turned on, the reference voltage Vcc is divided by the determination resistor  9  and the first battery identifying resistor  7   a  so that the divided voltage is detected by the microcomputer  50 . On the other hand, when the FET  121  is turned off, the reference voltage Vcc is divided by the determination resistor  9  and the series resistance of the first and second identifying resistors  7   a ,  7   b  so that the divided voltage is detected by the microcomputer  50 . 
         [0044]    A charge-control process for charging the battery pack  2  by the charging device  1  in the charging system  200  according to the present invention will be described, referring to  FIG. 2 . 
         [0045]    In this embodiment, the charging device  1  has an ability to charge the first type of battery pack  2  such as 4S1P and 5S1P types, and the second type of battery pack  2  such as 4S2P and 5S2P types. The 4S1P type of battery pack  2  has four series-connected battery cells  2   a , a first battery identifying resistor  7   a  of resistance “a”, and a second battery identifying resistor  7   b  of resistance “c”. The configuration is series connection. The 4S2P type of battery pack  2  has eight battery cells  2   a  and a first battery identifying resistor  7   a  of resistance “a”. The 4S2P type has no second battery identifying resistor  7   b . In the 4S2P type, two battery cells  2   a  are connected in parallel as a battery unit, and four battery units are connected in series to make the battery pack  2 . Accordingly, the configuration is parallel connection. 
         [0046]    The 5S1P type of battery pack  2  has five series-connected battery cells  2   a , a first battery identifying resistor  7   a  of resistance “b”, and a second battery identifying resistor  7   b  of resistance “d”. The configuration is series connection. The 5S2P type of battery pack  2  has ten battery cells  2   a  and a first battery identifying resistor  7   a  of resistance “d”. The 5S2P type has no second battery identifying resistor  7   b . In the 4S2P type, two battery cells  2   a  are connected in parallel to provide a battery unit, and four battery units are connected in series to make the battery pack  2 . Accordingly, the configuration is parallel connection. In the above case, the resistance a is smaller than the resistance b, and the sum of resistances (a+c) is equal to the sum of resistances (b+d). 
         [0047]    In Step  201 , the microcomputer  50  initializes the output ports  51   a  and S 1   b , when power is supplied. The display unit  130  then displays that the current condition is prior to charging. In this embodiment, the microcomputer  50  outputs a HIGH signal from the output port  51   a  through the resistor  133  to the display unit  130 , so that the display unit  130  lights up with red color to display that the charging device  1  is prior to charging. 
         [0048]    In Step  202 , the microcomputer  50  outputs a LOW signal from the output port S 1   b  through the resistor  142  to the switching unit  140  to turn on the FET  141 , before the battery pack is attached to the charging device  1 . Since the FET  141  is on, the reference voltage Vcc is ready for applying the battery pack  2 . 
         [0049]    In Step  203 , the microcomputer  50  determines whether or not the battery pack  2  has been attached to the charging device  1 . If the microcomputer  50  detects a change in the voltage appearing at the A/D port  52  receiving an output signal from the battery temperature detection unit  80 , the microcomputer  50  determines that the battery pack has been attached to the charging device  1 . 
         [0050]    In Step  204 , the microcomputer  50  determines at the time to how many battery cells  2   a  are connected in series in the battery pack  2 , based on the voltage inputted to the A/D port  52  from the determination resistor  9 . In this case, because the FET  141  is on, the reference voltage Vcc is applied to the gate terminal of the FET  121  in the battery pack  2  to turn on the FET  121 . Therefore, the reference voltage Vcc is applied across the series-connected the first battery identifying resistor  7   a  and the determination resistor  9 . 
         [0051]    The voltage obtained by dividing the voltage Vcc based on the ratio between the resistances of the determination resistor  9  and the first battery identifying resistor  7   a  is inputted to the A/D port  52  of the microcomputer  50 . For example, provided that the determination resistor  9  has a resistance of w. If the battery pack  2  has four cells connected in series, the voltage of Vcc×a/(a+w) is inputted to the A/D port  52 , as shown in  FIG. 3A  or  3 B. If the battery pack has five cells connected in series, the voltage of Vcc×b/(b+w) is inputted to the A/D port  52 , as shown in  FIGS. 3C and 3D . Thus, the voltage inputted to the A/D port  52  is changed according to the number of battery cells  2   a  connected in series, so that the microcomputer  50  determines based on the potential difference ΔV 1  at the A/D port  52  whether or not the battery pack  2  attached in the charging device  1  has four battery cells  2   a  connected in series. 
         [0052]    If the microcomputer  50  has determined that the battery pack  2  has four battery cells  2   a  connected in series in Step  204  ( FIGS. 3A and 3B ), the process goes to Step  205 , in which the microcomputer  50  turns off the FET  141  at the time t 1 . The microcomputer  50  turns off the FET  141  by outputting a HIGH signal from the output port  51   b  of the microcomputer  50  through the resistor  142  to the switching unit  140 . In Step  206 , the microcomputer  50  determines the type of battery pack  2 , the first type 1P or the second type 2P. How the microcomputer  50  determines the type of battery pack in Step  206  will be described as follows. 
         [0053]    Since the FET  141  is turned off in Step  205 , the FET  121  is also turned off at the time t 1 . When the FET  121  is turned off, the second battery identifying resistor  7   b  is operationally connected with the first battery identifying resistor  7   a  in series, if the battery pack  2  includes the second battery identifying resistor  7   b . Therefore, if the battery pack  2  has the second battery identifying resistor  7   b , the voltage obtained by dividing the voltage Vcc changes based on the ratio between the resistance of the determination resistor  9  and the series-connected resistances of the battery identifying resistors  7   a  and  7   b  and is inputted to the A/D port  52  of the microcomputer  50 , as shown in  FIG. 3B . In this embodiment, if the battery pack  2  is the first type 4S1P, the divided voltage is changed from Vcc×a/(a+w) to Vcc×(a+c)/((a+c)+w) due to the second battery identifying resistor  7   b  and inputted to the A/D port  52 , as shown in  FIG. 3B . If the battery pack  2  is the second type, the voltage: Vcc×a/(a+w) inputted to the A/D port  52  is not changed, as shown in  FIG. 3A . This is because the second type 4S2P has no second battery identifying resistor  7   b . The microcomputer  50  determines based on the potential difference ΔV 2  at the A/D port  52  whether the battery pack  2  is the first type or the second type. 
         [0054]    If the microcomputer  50  has determined that the battery pack  2  is the second type (Yes in Step  206 ), the microcomputer  50  determines that the battery pack  2  is a 4S2P type in Step  207 . In Step  208 , the microcomputer  50  sets a charging voltage for charging the 4S2P type of battery pack  2 , and then turns off the FET  112  to set the charging voltage for the 4S2P type. For example, the voltage of 16.8V is employed as the charging voltage for charging the 4S2P type of battery pack  2 . In Step  209 , the microcomputer  50  sets a charging current to I 1 . In order to set the charging current to I 1 , the microcomputer  50  outputs no signal from the output port S 1   b  so that the resistor  73  is not operationally and electrically connected to the series-connected resistors  71  and  72 . Accordingly, the charging current I 1  is set to 7.5 A, for example. 
         [0055]    If the microcomputer  50  has determined that the battery pack  2  is not the second type in Step  206 , the microcomputer  50  determines in Step  210  that the battery pack  2  is the 4S1P type. In Step  211 , the microcomputer  50  sets a charging voltage for the 4S1P type of battery pack  2 . The microcomputer  50  turns off the FET  112  to set the charging voltage for the 4S1P type. For example, the voltage of 16.8V is employed as the charging voltage for charging the 4S1P type. In Step  212 , the microcomputer  50  sets a charging current to the current I 2  (I 2 &lt;I 1 ). In order to set the charging current to I 2 , the microcomputer  50  outputs a LOW signal from the output port  51   b  to operationally connect the resistor  73  in parallel with the resistor  72 . Accordingly, the charging current 3.75 A is employed as the current value I 2 , for example. 
         [0056]    On the other hand, if the microcomputer  50  has determined that four battery cells  2   a  are not connected in series in the battery pack  2  in Step  204 , in other words, if the microcomputer  50  has determined that the battery pack  2  has five battery cells  2   a  connected in series, which is the 5S type. The microcomputer  50  turns off the FET  141  at the time t 1  in Step  213 . In order to turn off the FET  141 , the microcomputer  50  outputs a HIGH signal from the output port  51   b  through the resistor  142  to the switching unit  140 . 
         [0057]    In Step  214 , the microcomputer  50  determines whether or not the battery pack  2  is a 5S2P type. How the microcomputer  50  determines the type of the battery pack  2  in Step  214  will be given below. 
         [0058]    Since the FET  141  is turned off in Step  213 , the FET  121  is also turned off at the time t 1 . When the FET  121  is turned off, the second battery identifying resistor  7   b  is operationally connected with the first battery identifying resistor  7   a  in series, if the battery pack  2  includes the second battery identifying resistor  7   b . Therefore, if the battery pack  2  has the second battery identifying resistor  7   b , the voltage obtained by dividing the voltage Vcc changes based on the ratio between the resistance of the determination resistor  9  and the series-connected resistances of the battery identifying resistors  7   a  and  7   b  and is inputted to the A/D port  52  of the microcomputer  50 , as shown in  FIG. 3D . In this embodiment, if the battery pack  2  is the first 5S1P type, the divided voltage is changed from Vcc×b/(b+w) to Vcc×(b+d)/((b+d)+w) due to the second battery identifying resistor  7   b  and is inputted to the A/D port  52 , as shown in  FIG. 3D . If the battery pack  2  is the second type, the voltage: Vcc×b/(b+w) inputted to the A/D port  52  is not changed, as shown in  FIG. 3C . This is because the second type 5S2P has no second battery identifying resistor  7   b . The microcomputer  50  determines based on the potential difference ΔV 3  at the A/D port  52  whether the battery pack  2  is the first type or the second type. 
         [0059]    If the microcomputer  50  has determined that the battery pack  2  is the second type (Yes in Step  214 ), the microcomputer  50  determines that the battery pack  2  is a 5S2P type in Step  215 . In Step  216 , the microcomputer  50  sets a charging voltage for charging the 5S2P type of battery pack  2 , and then turns on the FET  112  to set the charging voltage for the 5S2P type. For example, the voltage of 21V is employed as the charging voltage for charging the second type of battery pack  2 . In Step  217 , the microcomputer  50  sets a charging current to I 1 . In order to set the charging current to I 1 , the microcomputer  50  outputs no signal from the output port  51   b  so that the resistor  73  is not operationally connected to the series-connected resistors  71  and  72 . Accordingly, the charging current I 1  is set to 7.5 A, for example. 
         [0060]    If the microcomputer  50  has determined that the battery pack  2  is not the second type in Step  214 , the microcomputer  50  determines in Step  218  that the battery pack  2  is a 5S1P type. In Step  219 , the microcomputer  50  sets a charging voltage for the 5S1P type of battery pack  2 . The microcomputer  50  turns on the FET  112  to set the charging voltage for the 5S1P type. For example, the voltage of 21V is employed as the charging voltage for charging the 5S1P type. In Step  220 , the microcomputer  50  sets a charging current to the current I 2  (I 2 &lt;I 1 ). In order to set the charging current to I 2 , the microcomputer  50  outputs a LOW signal from the output port  51   b  to operationally and electrically connect the resistor  73  in parallel with the resistor  72 . Accordingly, the charging current 3.75 A is employed as the current value I 2 , for example. 
         [0061]    After the microcomputer  50  sets the charging voltage and the charging current as described above, in Step  221 , the microcomputer  50  outputs a LOW signal from the output port  51   b  through the resistor  142  to the switching unit  140  to turn on the FET  141  at the time t 2  again. 
         [0062]    In Step  222 , the microcomputer  50  outputs a LOW signal from the output port  51   a  to the PWM control IC  23  through the charging control signal transmission unit  4  to start charging the battery pack  2 . In Step  223 , while the charging device  1  is charging the battery pack  2 , the LEC  131  in the display unit  130  lights up with orange color and indicates that the battery pack  2  is in a process for charging. In other words, the microcomputer  50  outputs a HIGH signal from the output port  51   a  through the resistors  132  and  133  to the display unit  130 , so that the display unit  130  lights up with orange color to display the charging state. 
         [0063]    In Step  224 , while the charging device  1  is charging the battery pack  2 , the microcomputer  50  determines whether or not the battery pack  2  is the second type. The type of the battery pack  2  has been determined in Step  206  or Step  214 . If the microcomputer  50  has determined that the battery pack  2  is the second type, the microcomputer  50  determines whether or not the actual charging current is equal to or smaller than I 3  (I 3 &lt;I 1 ) in Step  225 . For example, it is assumed that the current of 3 A is employed as the current value I 3 . In this embodiment, the charging device  1  charges the battery pack  2  under constant current and constant voltage charging control. When the charging voltage reaches a predetermined value, the microcomputer  50  starts decreasing the charging current. After that, when the charging current reaches another predetermined value which is smaller than the predetermined value, the microcomputer  50  determines that the battery pack  2  has been fully charged. If the microcomputer  50  has determined that the charging current is equal to or smaller than I 3  in Step  225 , the microcomputer  50  determines that the battery pack  2  has been fully charged. In order to stop charging, the microcomputer  50  outputs a HIGH signal from the output port  51   a  through the photocoupler  4  to the PWM control IC  23 , thereby stopping the operation of the PWM control IC  23 . It is noted that the current value I 3  may be adjusted or changed depending on the cell configuration of the battery pack  2 . 
         [0064]    If the microcomputer  50  has determined that the battery pack  2  is not the second type in Step  224 , the microcomputer  50  determines in Step  226  whether or not the charging current is equal to or smaller than I 4  (I 4 &lt;I 2 ). For example, it is assumed that 1.5 A is employed as the current value I 4 . It is noted that the current value I 4  may be adjusted or changed depending on the cell configuration of the battery pack  2 . In this embodiment, the charging device  1  charges the battery pack  2  at constant current and constant voltage charging control. When the charging voltage reaches a predetermined value, the microcomputer  50  starts decreasing the charging current. After that, when the charging current reaches another predetermined value which is smaller than the predetermined value, the microcomputer  50  determines that the battery pack  2  has been fully charged. If the microcomputer  50  has determined that the charging current is equal to or smaller than I 4  in Step  226 , the microcomputer  50  determines that the battery pack  2  has been fully charged in Step  227 . In order to stop charging, the microcomputer  50  outputs a HIGH signal from the output port  51   a  through the photocoupler  4  to the PWM control IC  23 , thereby stopping the operation of the PWM control IC  23 . 
         [0065]    After the charging the battery pack  2  is over, the display unit  130  lights up with green color to display the stop state in Step  228 . In order to light the display unit  130  with green color, the microcomputer  50  outputs a HIGH signal from the output port  51   a  through the resistor  133  to the display unit  130 . In Step  229 , the microcomputer  50  determines whether the battery pack  2  is removed from the charging device  1 . If the battery pack  2  is removed from the charging device  1 , the process returns to Step  201 . 
         [0066]      FIG. 4  shows another charging system having a conventional charging device  1  without the switching unit  140 , in which the charging device  1  charges the battery pack  2  according to the present invention. 
         [0067]    Since the switching unit  140  shown in  FIG. 1  is not provided in the charging device  1 , the voltage Vcc is constantly applied to the gate terminal of the FET  121  to maintain the FET  121  on. Therefore, the voltage obtained by dividing the voltage Vcc based on the ratio between the resistance values of the determination resistor  9  and the battery identifying resistor  7   a  is inputted to the A/D port  52  of the microcomputer  50 . For example, provided that the first battery identifying resistor  7   a  corresponding to four cells connected in series has a resistance of a, another first battery identifying resistor  7   a  corresponding to five cells connected in series has a resistance of b, and the determination resistor  9  has a resistance of w, either one of the following voltages is inputted to the A/D port  52  of the microcomputer  50 . If the battery pack  2  has four battery cells  2   a  connected in series, the voltage of Vcc×a/(a+w) is inputted to the A/D port  52 . If the battery pack  2  has five battery cells  2   a  connected in series, the voltage of Vcc×b/(b+w) is inputted to the A/D port  52 . The microcomputer  50  determines based on the potential difference at the A/D port  52  whether or not the battery pack  2  attached in the charging device  1  has four battery cells  2   a  connected in series. In this case, the microcomputer  50  merely determines the number of the battery cells  2   a  connected in series in the battery pack  2 . And, the microcomputer  50  cannot determine whether the battery pack  2  is the first type or the second type. However, the charging device  1  is able to charge the battery pack  2  according to the present invention, depending on the number of battery cells  2   a  connected in series in the battery pack  2 . In this case, if the charging current is set for the first type of the battery pack  2  such as 4S1P or 5S1P type, charging the battery cells  2   a  by using the set charging current does not cause any trouble to shorten the life of the battery pack  2  regardless of the type of the battery pack  2 . 
         [0068]    As described above, the battery type identifier  7  of the battery pack  2  has two different battery identifying resistors  7   a  and  7   b : the first battery identifying resistor  7   a  identifying the number of battery cells  2   a  connected in series, and the second battery identifying resistor  7   b  identifying the configuration of the battery cells  2   a  in the battery pack  2 . The charging device  1  determines the cell configuration and the number of battery cells  2   a  by two stages. Accordingly, the cell configuration and the number of battery cells  2   a  in the battery pack  2  can be determined precisely, compared with the battery pack  2  having a single battery identifying resistor. In other words, an accuracy to determine the configuration of the battery pack  2  can be improved. 
         [0069]    On the other hand, the charging device  1  has the switching unit  140  to control an application of the reference voltage to the battery pack  2  and assist in determining the configuration of the battery pack  2  and the number of series-connected battery cells  2   a  in the battery pack  2 . Accordingly, the charging device  1  can determine the type of battery pack  2  and the configuration thereof precisely, compared with a conventional charging device. More precisely, the battery pack has two different battery pack identifying resistors; one being used to determine the number of battery cells connected in series, the other being used to determine the arrangement of the battery cells, 1P or 2P. On the other hand, the charging device determines the configuration of battery cell in the batter pack at two stages, so that the configuration of battery cell in the batter pack can be determined more precisely, thereby avoiding the shortening the lifetime of the battery pack and any damage to the battery pack. 
         [0070]    It should be noted the number of battery cells  2   a  connected in series is not limited to four or five as described above. Any number of series-connected battery cells  2   a  is fall into the scope of the present invention.