Abstract:
A battery pack including at least one secondary battery and supplying power to predetermined equipment is disclosed. In the battery pack, charging current to the secondary battery supplied from an external charging device is cut oft to suspend charging the secondary battery until receiving a predetermined instruction from the external charging device. 
     The battery pack may comprise a first communication circuit unit for communicating with the external charging device; a first switching circuit unit for cutting off the charging current from the external charging device to the secondary battery; and a control circuit unit for controlling the first switching circuit unit based on information received by the first communication circuit unit. The control circuit unit instructs the first switching circuit unit to cut off the charging current from the external charging device to the secondary battery and suspend charging the secondary battery until receiving the predetermined instruction from the external charging device via the first communication circuit unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a battery pack having a secondary battery and a charging system using the battery pack, and specifically relates to charging/discharging control of the battery pack containing ID information for identifying the battery pack having the secondary battery. 
         [0003]    2. Description of the Related Art 
         [0004]    In prior art battery pack charging systems, battery packs have a special shape which can be adapted to a specific charging device, and therefore only specific battery packs can be charged by the specific charging device. However, battery charging capacities are increasing as technology progresses; a newer battery pack having the same shape has a larger charging capacity. 
         [0005]    A prior art battery pack charging device always performs the same control for a battery pack attached to the charging device. Accordingly, if a battery pack having the same shape but a larger charging capacity is attached to the prior art battery charging device, it may take a longer time to fully charge the battery pack. On the other hand, if a battery pack having the same shape but a smaller charging capacity is attached to the prior art battery charging device, the battery charging device may supply a charging current larger than rated current to the battery pack and may shorten the battery service life. 
         [0006]    In order to solve the problem, the battery pack may have ID information unique to the battery pack, as disclosed in Japanese Patent Publication No. 06-81425. When starting charging the battery pack, a battery charging device may obtain the ID information of the battery pack, and based on the obtained ID information, the battery charging device may receive battery information such as charging capacity to be utilized for charge control. 
         [0007]    However, in prior art battery pack charging systems, battery packs have a special shape which can be adapted to a specific charging device. Accordingly, only if a battery pack can be attached to a charging device, the charging operation is automatically started without checking whether proper ID information is obtained. Therefore inadequate charging may be performed resulting in failures of the battery pack and the charging device. 
         [0008]    Even if a battery pack has its ID information, in a case where a charging device does not have an ID recognizing function, inadequate charging may be performed resulting in failures or short service lives of the battery pack and the charging device. 
         [0009]    Further, when a battery pack is attached to off-specification equipment, or the battery pack is shortened, current larger than specification current may flow resulting in failure of the battery pack. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, it is a general object of the present invention to provide a battery pack having a secondary battery and a charging system using the battery pack, which can prevent failures of the battery pack and a charging device by preventing improper charging/discharging even if the battery pack is attached to an inadequate charging device. 
         [0011]    Features and advantages of the present invention are set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by a charging system particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention. 
         [0012]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides as follows. 
         [0013]    According to one feature of the present invention, there is provided a battery pack including at least one secondary battery and supplying power to predetermined equipment, characterized in that charging current to the secondary battery supplied from an external charging device is cut off to suspend charging the secondary battery until receiving a predetermined instruction from the external charging device. 
         [0014]    The battery pack may comprise a first communication circuit unit for communicating with the external charging device; a first switching circuit unit for cutting off the charging current from the external charging device to the secondary battery; and a control circuit unit for controlling the first switching circuit unit based on information received by the first communication circuit unit; wherein the control circuit unit instructs the first switching circuit unit to cut off the charging current from the external charging device to the secondary battery and suspend charging the secondary battery until receiving the predetermined instruction from the external charging device via the first communication circuit unit. 
         [0015]    According to another feature of the present invention, there is provided a charging system comprising a battery pack including at least one secondary battery, and a charging device for charging the battery pack, characterized in that the charging device communicates with the battery pack in a predetermined manner when receiving a DC power supply for charging the secondary battery, and when the charging device cannot communicate with the battery pack, the charging device suspends charging the secondary battery. 
         [0016]    According to embodiments of the present invention, if a battery pack is connected to an inadequate charging device such as an off-standard charging device, it is possible to stop the charging operation. When the battery pack is connected to equipment other than equipment with a proper main body, the charging system allows the secondary battery to discharge but prevents charging of the secondary battery, and therefore it is possible to prevent the failure or short service life of the battery pack. 
         [0017]    Under the situation where the charge control circuit cannot communication with the battery pack, cannot obtain any ID information from the battery pack, or determines that the ID information obtained from the battery pack is invalid, the charge control circuit stops the charging current from flowing to the battery pack and instructs the control circuit to prevent charging by having the protection circuit turn off a transistor. However, under the same situation, the charge control circuit can prevent the battery pack from discharging as well as stop the charging current from flowing to the battery pack. 
         [0018]    Before starting to charge the battery pack, the charge control circuit checks the ability to communicate with the battery pack. If communication is impossible, the charging of the battery pack is not carried out. If communication is possible, then the charge control circuit determines whether there is ID information for the battery pack. If there is no ID information or invalid information, the charge control circuit prevents charging and discharging since an attached battery pack cannot be properly charged by the main body, and therefore failures due to mismatching between the battery pack and the charging device can be prevented. If the ID information is valid, based on the battery information obtained from the remainder detection circuit of the battery pack, it is possible to select the optimum charging method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Other objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a block diagram of a charging system according to an embodiment of the present invention; 
           [0021]      FIG. 2  is a flowchart showing an operational procedure of the charging system shown in  FIG. 1 ; and 
           [0022]      FIG. 3  is a flowchart showing another operational procedure of the charging system shown in  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    In the following, embodiments of the present invention are described with reference to the accompanying drawings. 
         [0024]      FIG. 1  is a block diagram illustrating a charging system for charging a secondary battery according to an embodiment of the present invention. The charging system includes a battery pack including a secondary battery. 
         [0025]    As shown in  FIG. 1 , the charging system  1  comprises the battery pack  2  including a secondary battery or rechargeable battery  11 , and a main body  3  having a function of charging the battery pack  2  and being connected to the battery pack  2  to perform predetermined other functions. A charging DC power supply  10  for charging the battery pack  2  is connected to the main body  3 . 
         [0026]    The battery pack  2  comprises at least one secondary battery  11  such as a lithium battery, a control circuit  12  for controlling an electronic circuit contained in the battery pack  2 , a communication circuit  13  for transmitting and receiving information to and from the main body  3 , a remainder detection circuit  14  that measures a charging/recharging current, voltage and temperature of the secondary battery  11  to determine the remaining energy of the secondary battery  11 . The battery pack  2  further comprises NMOS transistors M 1 , M 2  and a protection circuit  15 . The protection circuit  15  turns off the NMOS transistor M 1  to cut a charging current to the secondary battery  11  when it detects any abnormality during the charging period of the secondary battery  11 , and turns off the NMOS transistor M 2  to cut a discharging current from the secondary battery  11  when it detects any abnormality during the discharging period of the secondary battery  11 . 
         [0027]    The battery pack  2  further comprises a current detection resistance R 1  for detecting a charging/discharging current of the secondary battery  11 , a thermometer  16  for measuring a temperature of the secondary battery  11 , and an ID storage circuit  17  for storing many pieces of information unique to the battery pack  2 . The control circuit  12 , the communication circuit  13 , the remainder detection circuit  14 , the protection circuit  15  and the ID storage circuit  17  are connected to each other via an internal bus  18 . The control circuit  12  is an example of the control circuit unit, the communication circuit  13  is an example of the first communication circuit unit, and the remainder detection circuit  14 , the thermometer  1 E and the resistance R 1  are an example of the remainder detection circuit unit. The protection circuit  15  and the NMOS transistor M 1  are an example of the first switch circuit unit, and the protection circuit  15  and the NMOS transistor M 2  are an example of the second switch circuit unit. The ID storage circuit  17  is an example of the storage circuit unit. 
         [0028]    A positive electrode of the secondary battery  11  is connected to a power supply terminal Va+. Between a negative electrode of the secondary battery  11  and a power supply terminal Va−, the resistance R 1  and the NMOS transistors M 2  and M 1  are serially connected. A substrate gate is connected to the NMOS transistor M 1  so as to form a parasitic diode D 1  in the direction from the power supply terminal Va− to the NMOS transistor M 2 . A substrate gate is connected to the NMOS transistor M 2  so as to form a parasitic diode DZ in the direction from the resistance R 1  to the NMOS transistor M 1 . 
         [0029]    The communication circuit  13  is connected to an input/output terminal IFa that is a communication terminal of the battery pack  2 . A voltage of the power supply terminal Va+ is input to the remainder detection circuit  14 . To the remainder detection circuit  14 , the thermometer  16  is connected and a voltage across the resistance R 1  is input. The protection circuit  15  controls the switching of the NMOS transistors M 1  and M 2  in accordance with a control signal input via the internal bus  18  from the control circuit  12 . Every circuit in the battery pack  2  has power supplied from the secondary battery  11 , although not shown in  FIG. 1 . 
         [0030]    The main body  3  comprises a charge control circuit  21  for controlling the charge to the secondary battery  11  in the battery pack  2 , a communication circuit  22  for communicating information with the battery pack  2 , and a load  23  having a predetermined function. The charge control circuit  21  and the communication circuit  22  are connected via an internal bus  24 . The charge control circuit  21  is connected to power supply terminals Vb+ and Vb− of the main body  3 , and connected to a power supply input terming DCin+, to which a positive electrode of the charging DC power supply  10  is connected. The communication circuit  22  is connected to the power supply terminal Vb− and Vb+ of the main body  3 , and an input/output terminal IFb that is a communication terminal of the main body  3 . The main body  3  is an example of the charging device, the charge control circuit  21  is an example of the charge control circuit unit, and the communication circuit  22  is an example of the second communication circuit unit. 
         [0031]    The load  23  is connected to the power supply terminal Vb+ and Vb− of the main body  3 . The power supply terminal Vb− of the main body  3  is connected to the power supply input terminal DCin−, to which a negative electrode of the charging DC power supply  10  is connected. When the battery pack  2  is attached to the main body  3 , the power supply Va+ of the battery pack  2  is connected to the power supply Vb+ of the main body  3 , the power supply va of the battery pack  2  is connected to the power supply Vb− of the main body  3 , and the input/output terminal IFa of the battery pack  2  is connected to the input/output terminal IFb of the main body  3 . 
         [0032]    In this structure, the control circuit  12  detects from the remainder detection circuit  14  that the voltage of the secondary battery  11  is lowered to a predetermined value α. If the control circuit  12  determines that the secondary battery  11  will become over-discharged if the battery continues to discharge, the control circuit  12  instructs the protection circuit  15  to turn off the NMOS transistor M 2  to cut the discharging current from the secondary battery  11  and prevent it from becoming over-discharged. When the control circuit  12  determines from the remainder detection circuit  14  that the voltage of the secondary battery  11  is not lowered to the predetermined value α, the control circuit  12  instructs the protection circuit  15  to keep the NMOS transistor M 2  on. This controlling operation for the NMOS transistor M 2  is carried out even while the communication circuit  13  cannot communicate with the main body because the battery pack  2  is not connected to the main body  3  and the battery pack  2  is connected to other inadequate equipment instead of the main body  3 , with which the communication circuit  13  cannot perform normal communication. 
         [0033]      FIG. 2  is a flowchart illustrating a charging operation procedure of the charging system shown in  FIG. 1 . The charging operation of the charging system  1  is explained below with reference to  FIG. 2 . 
         [0034]    As shown in  FIG. 2 , after the procedure starts, the charge control circuit  21  first detects whether the charging DC power supply  10  is connected to the power supply input terminals DCin+ and DCin− at step S 1 . If the charge control circuit  21  does not detect that the charging DC power supply  10  is connected (NO), the charge control circuit  21  continues the detecting operation. On the other hand, if the charge control circuit  21  detects that the charging DC power supply  10  is connected (YES), the charge control circuit  21  determines whether the communication circuit  21  can communicate with the battery pack  2  at step S 2 . At step S 2 , if the communication circuit  22  cannot communicate with the battery pack  2  (NO), it is most likely that the battery pack  2  is not connected or an off-specification battery pack is connected. Then the charge control circuit  21  stops charging the battery pack  2  at step S 12  and the procedure ends. 
         [0035]    If the communication circuit  22  can communicate with the battery pack  2  at step S 2  (YES), the charge control circuit  21  communicates with the battery pack  2  via the communication circuit  22 , and requests the battery pack  2  to send its ID information at step S 3 . Next, the charge control circuit  21  determines whether ID information is sent from the battery back  2  at step S 4 . If no ID information is sent from the battery pack  2  (NO), the procedure goes to step S 13 , which is explained below. If the charge control circuit  21  receives the ID information from the battery pack  2  (YES), the charge control circuit determines whether the received ID information is valid at step S 5 . 
         [0036]    Next, the operation of the battery pack  2  when the charge control circuit  21  requests ID information is explained. The charge control circuit  21  requests the battery pack  2  via the communication circuit  22  to send ID information, and the request is received at the communication circuit  13  of the battery pack  2  and sent via the internal bus  18  to the control circuit  12 . In accordance with the request for ID information from the charge control circuit  21 , the control circuit  12  reads out ID information from the ID information storage circuit  17  via the internal bus  18 , and sends the read ID information to the communication circuit  22  via the internal bus  18  and the communication circuit  13 . The communication circuit  22  sends the received ID information to the charge control circuit  21 . 
         [0037]    If the charge control circuit  21  determines that the received ID information is invalid at step S 5  (NO), the procedure goes to step S 13 , which is explained below. On the other hand, if the charge control circuit  21  determines that the received ID information is valid (YES), the charge control circuit  21  obtains battery information from the battery pack  2  via the communication circuit  13  and the communication circuit  22  at step S 6 . The battery information includes the ID information stored in the ID information circuit  17  and a voltage, temperature, current and remaining amount (energy) of the secondary battery  11  detected by the remainder detection circuit  14 . Next, the charge control circuit  21  analyzes the battery information obtained from the battery pack  2 , and determines a charging method at step S 7 . In more specifically, based on the full capacity and the present remaining amount (energy) of the secondary battery  11 , the charge control circuit  21  determines a charging specification, for example, selects either constant current charging or constant voltage charging, and determines how much current to use when selecting the constant current charging method. 
         [0038]    After the charge control circuit  21  determines the charging method, the charge control circuit  21  supplies the charging current to the secondary battery  11  of the battery pack  2 , and sends a charge allowance instruction to the battery pack  2  via the communication circuit  22  and the communication  13 . The control circuit  12  receives the charge allowance instruction and instructs the protection circuit  15  to turn on the NMOS transistor M 1  at step S 8 . At this timing, the charging of the secondary battery  11  starts. During the charging of the secondary battery  11 , the charge control circuit  21  obtains necessary battery information of the secondary battery  11  one item after another from the control circuit  12  via the communication circuit  13  and the communication circuit  22  at step S 9 . Thereafter, based on the obtained battery information, the charge control circuit  21  determines whether the charge is finished at step S 10 . If the charge is finished (YES), the charge control circuit  21  stops the charging current supplied to the battery pack  2  at step S 11  and the procedure ends. On the other hand, if the charge is not finished yet (NO), the procedure goes back to step S 9 . 
         [0039]    If there is no ID information at step S 4  (NO), or the obtained ID information is invalid (NO) at step S 5  (NO), the charge control circuit  21  stops the charging current supplied to the battery pack  2  and instructs the battery pack  2  to prevent the charging. The control circuit  12  receives the instruction and instructs the protection circuit  15  to turn off the transistor M 1  so as not to allow the charging current to flow to the secondary battery  11  at step S 13 , and the procedure ends. 
         [0040]    In this case, since the charge control circuit  21  and an attached battery pack  2  can communicate with each other (YES at step S 2 ), the attached battery pack  2  may be a standard one but may be out of order. Therefore, in order to prevent causing an inconvenient situation, the NMOS transistor M 1  is turned off. In order to turn off the transistor M 1 , the charge control circuit  21  instructs the control circuit  12  via the communication circuit  22  and the communication circuit  13 , to have the protection circuit  15  turn off the transistor M 1 . Then the procedure ends. 
         [0041]    When the communication circuit  13  cannot perform communication such as where the battery pack  2  is not connected to the main body  3  or is connected to inadequate equipment, the protection circuit  15 , based on the instruction from the control circuit  12 , turns off the transistor M 2 . If the battery pack  2  is connected to an inadequate charging device, the protection circuit  15 , based on the instruction from the charging device, turns off the transistor M 1 . In this manner, it is possible to stop the charging operation when the battery pack  2  is connected to an off-standard charging device. When the battery pack  2  is connected to equipment other than the main body  3 , this system allows the secondary battery  11  to discharge but prevents charging of the secondary battery  11 , and therefore it is possible to prevent the failure or short service life of the battery pack  2 . 
         [0042]    In the above embodiment, under the situation where the charge control circuit  21  cannot communication with the battery pack  2 , cannot obtain any ID information from the battery pack  2 , or determines that the ID information obtained from the battery pack  2  is invalid, the charge control circuit  21  stops the charging current to the battery pack  2  and instructs the control circuit  12  to prevent charging by having the protection circuit  15  turn off the transistor M 1 . However, under the same situation, the charge control circuit  21  can prevent the battery pack  2  from discharging as well as stopping the charging current from flowing to the battery pack  2 . In this case, the charge control circuit  21  instructs the control circuit  12  to prevent charging and discharging by turning off the NMOS transistors M 1  and M 2 , as well as stopping the charging current from flowing to the battery pack  2 . 
         [0043]    In this case, the procedure becomes that shown in  FIG. 3 . In  FIG. 3 , the same or similar steps are assigned the same reference numerals as in  FIG. 2 , and their explanations are omitted here. 
         [0044]      FIG. 3  is different from  FIG. 2  in that step  13  in  FIG. 2  is replaced with step  21  in  FIG. 3 . 
         [0045]    In the procedure shown in  FIG. 3 , if there is no ID information at step S 4  or the obtained ID information is invalid at step S 5 , the charge control circuit  21  stops the charging current to the battery pack  2  and instructs the battery pack  2  to prevent charging and discharging. The control circuit  12  receives the instruction, and causes the protection circuit  15  to turn off the NMOS transistors M 1  and M 2  to prevent the charging current from flowing to the secondary battery  11  and discharging current from flowing from the secondary battery  11 . Then the procedure ends. 
         [0046]    In this case, since the charge control circuit  21  and an attached battery pack  2  can communicate with each other (YES at step S 2 ), the attached battery pack  2  may be a standard one but may be out of order. Therefore, in order to prevent causing an inconvenient situation, the NMOS transistors M 1  and M 2  are turned off. In order to turn off the transistors M 1  and M 2 , the charge control circuit  21  instructs the control circuit  12  via the communication circuit  22  and the communication circuit  13 , to have the protection circuit  15  turn off the transistors M 1  and M 2 . Then the procedure ends. 
         [0047]    In this manner, before starting to charge the battery pack  2 , the charge control circuit  21  checks the ability to communicate with the battery pack  2 . If communication is impossible, charging to the battery pack  2  is not carried out. If communication is possible, then the charge control circuit  21  checks for ID information for the battery pack  2 . If there is no ID information or invalid information, the charge control circuit  21  prevents charging and discharging since the attached battery pack  2  cannot be properly charged by the main body  3 , and therefore failures due to mismatching between the battery pack and the charging device can be prevented. If the ID information is valid, based on the battery information obtained from the remainder detection circuit  14  of the battery pack  2 , it is possible to select the optimum charging method. 
         [0048]    The present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
         [0049]    The present application is based on Japanese Priority Application No. 2004-211490 filed on Jul. 20, 2004 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.