Abstract:
A battery protection device protects a battery from an abnormal state. The battery protection device includes a detector that detects an abnormality of the battery and outputs an abnormality detection signal when the abnormality is detected. A current is input to an input terminal from outside. A voltage converter converts the current input to the input terminal to voltage and outputs the voltage. A combiner combines the abnormality detection signal with the voltage and outputs a combined signal. A current converter converts the combined signal to a current. An output terminal outputs the current.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to battery protection devices, battery protection systems using the battery protection devices, and battery protection methods, and more particularly, to a battery protection device, a battery protection system, and a battery protection method that detect overcharge and over-discharge of a battery and control a switching element.  
         [0003]     2. Description of the Related Art  
         [0004]     In terms of its energy density and charging/discharging characteristics, lithium ion batteries have been attracting attention as secondary batteries that are repeatedly used by being charged. However, since the characteristics of lithium ion batteries are apt to be degraded due to over-discharging and overcharging, it has been necessary to protect lithium ion batteries with battery protection systems.  
         [0005]      FIG. 1  is a circuit diagram of a conventional battery protection system  1 .  
         [0006]     In the case where n batteries  11  are connected in series in the conventional battery protection system  1 , both ends of each of the n batteries  11  are connected to corresponding terminals T 11  through Tn+1, thereby monitoring the n batteries  11  with a protection IC  12 . When the protection IC  12  detects an over-discharged state or overcharged state of the n batteries  11 , terminals T 21  and T 22  supply abnormality detection signals to driver circuits  13  and  14 , respectively. The driver circuits  13  and  14  control the gate voltages of MOS transistors M 1  and M 2  in accordance with the abnormality detection signals from the terminals T 21  and T 22  of the protection IC  12 , thereby turning OFF the MOS transistors M 1  and M 2 , respectively. The drains and sources of the MOS transistors M 1  and M 2  are connected in series between the batteries  11  and a terminal T 1 . When the MOS transistors M 1  and M 2  are turned OFF, the batteries  1  and the terminal T 1  are disconnected, and discharging or charging is stopped. In the aforementioned manner, the batteries  11  are protected from discharging and overcharging.  
         [0007]     In the battery protection system  1  as shown in  FIG. 1 , it is necessary for the single protection IC  12  to protect the batteries connected in series. Thus, when the number of batteries is increased, a high voltage is applied to the protection IC  12 , and the protection IC  12  may not be able to withstand the high voltage. Hence, it has been possible to protect merely several batteries connected in series. Accordingly, there is a demand for a battery protection system capable of protecting a large number of batteries connected in series.  
         [0008]     As for battery protection systems capable of protecting a large number of batteries connected in series, there has been proposed a system for protecting batteries by performing abnormality detection by: dividing portions to be detected into blocks for each battery; sequentially transmitting abnormality detection information from a high-voltage side to a low-voltage side; and turning OFF a switching element connected in series to the batteries in response to the abnormality detection information output from the last block (refer to, for example, Japanese Laid-Open Patent Application No. 2001-307782).  
         [0009]     However, since conventional battery management systems perform level shifting by detecting the voltages of the adjacent protection blocks, there have been problems in that it is difficult or impossible to separately drive blocks and that wiring becomes complex.  
         [0010]     Additionally, it has been necessary in conventional battery management systems to connect plural protection blocks in a predetermined order.  
       SUMMARY OF THE INVENTION  
       [0011]     A general object of the present invention is to provide an improved and useful battery protection device, battery protection system, and battery protection method in which one or more of the above-mentioned problems are eliminated.  
         [0012]     Another and more specific object of the present invention is to provide a battery protection device, a battery protection system, and a battery protection method that can separately detect the state of each battery with a simple circuit configuration.  
         [0013]     In order to achieve the above-mentioned objects, according to one aspect of the present invention, there is provided a battery protection system ( 100 ) for protecting a plurality of batteries ( 111 - 1  through  111 - n ) connected in series from an abnormal state,  
         [0014]     the battery protection system comprising:  
         [0015]     a switching element (M 1 , M 2 ) connected to the batteries ( 111 - 1  through  111 - n ) in series;  
         [0016]     a plurality of battery protection devices ( 113 - 1  through  113 - n ) that are provided for the batteries ( 111 - 1  through  111 - n ) in a corresponding manner, detect an abnormal state of the corresponding batteries ( 111 - 1  through  111 - n ), and output an abnormality detection signal; and  
         [0017]     a drive circuit ( 114 ,  115 ) that drives the switching element (M 1 , M 2 ) in accordance with the abnormality detection signal,  
         [0018]     each of the battery protection devices ( 113 - 1  through  113 - n ) comprising:  
         [0019]     a detector ( 211 , R 21 , R 22 ,  231 ,  232 ) that detects an abnormality of a corresponding one of the batteries ( 111 - 1  through  111 - n ) and outputs the abnormality detection signal when the abnormality is detected;  
         [0020]     an input terminal (T 15 , T 16 ) to which a current is input from outside;  
         [0021]     a voltage converter ( 233 ) that converts the current input to the input terminal (T 15 , T 16 ) to voltage and outputs the voltage;  
         [0022]     a combiner (M 11  through M 17 ,  234 ) that combines the abnormality detection signal with the voltage and outputs a combined signal;  
         [0023]     a current converter (M 18 , M 19 ) that converts the combined signal to a current; and  
         [0024]     an output terminal (T 13 , T 14 ) that outputs the current,  
         [0025]     wherein the battery protection devices ( 113 - 1  through  113 - n ) are connected to each other such that the output terminal (T 13 , T 14 ) of one of the battery protection devices ( 113 -(i−1) is connected to the input terminal (T 15 , T 16 ) of a subsequent one of the battery protection devices ( 113 - i ), and  
         [0026]     the output terminal (T 13 , T 14 ) of one of the battery protection devices of a last stage ( 113 - n ) is connected to the drive circuit ( 114 ,  115 ).  
         [0027]     Additionally, each of the battery protection devices ( 113 - 1  through  113 - n ) may be formed by a semiconductor integrated circuit chip.  
         [0028]     It should be noted that the above reference numerals in parentheses are merely examples, and not intended to limit the scope of the claims.  
         [0029]     In an embodiment of the present invention, plural battery protection devices are provided for plural batteries connected in series in a corresponding manner. The battery protection devices are connected to each other such that the output terminal of one of the battery protection devices is connected to the input terminal of a subsequent one of the battery protection devices in a sequential manner. The output terminal of the battery protection device of the last stage is connected to a drive circuit, which perform switching of a switching element. Accordingly, it is possible to separately detect the state of each of the batteries and to protect plural batteries with a simple circuit configuration.  
         [0030]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the following drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a circuit diagram of a conventional battery protection system;  
         [0032]      FIG. 2  is a system block diagram of a battery protection system according to one embodiment of the present invention;  
         [0033]      FIG. 3  is a circuit diagram of a protection IC;  
         [0034]      FIG. 4  is a circuit diagram of an overcharge detection circuit;  
         [0035]      FIG. 5  is a circuit diagram of an over-discharge detection circuit;  
         [0036]      FIG. 6  is a circuit diagram of a drive circuit; and  
         [0037]      FIG. 7  is a circuit diagram of a battery protection system according to a variation of the embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0000]     (System Structure)  
         [0038]      FIG. 2  is a system circuit diagram of a battery protection system  100  according to one embodiment of the present invention.  
         [0039]     The battery protection system  100  includes n batteries  111 - 1  through  111 - n , MOS transistors M 1  and M 2 , resistances R 1  and R 2 , filter circuits  112 - 1  through  112 - n , protection ICs  113 - 1  through  113 - n , and drive circuits  114  and  115 .  
         [0040]     The n batteries  111 - 1  through  111 - n  are connected in series. One end of the n serially connected batteries  111 - 1  through  111 - n  is connected to a terminal T 1  via MOS transistors M 1  and M 2  whose sources and drains are connected in series. The other end of the n serially connected batteries  111 - 1  through  111 - n  is connected to a terminal T 2 .  
         [0041]     The filter circuits  112 - 1  through  112 - n  and the protection ICs  113 - 1  through  113 - n  are provided to correspond to the batteries  111 - 1  through  111 - n , respectively.  
         [0042]     Hereinafter, it is assumed that a filter circuit  112 - i  represents one of the filter circuits  112 - 1  through  112 - n . In addition, it is assumed that a battery  111 - i  represents one of the batteries  111 - 1  through  111 - n . Further, it is assumed that a protection IC  113 - i  represents one of the protection circuits  113 - 1  through  113 - n.    
         [0000]     (Filter Circuits  112 - i )  
         [0043]     The filter circuit  112 - i  includes a resistance R 11  and a capacitor C 11 . The filter circuit  112 - i  is connected to both ends of the battery  111 - i  and removes a noise component of voltage produced across the battery  111 - i.    
         [0000]     (Protection IC  113 - i )  
         [0044]      FIG. 3  is a circuit diagram of the protection IC  113 - i.    
         [0045]     The protection IC  113 - i  is formed by a semiconductor IC chip. The protection IC  113 - i  is a circuit that detects overcharge and over-discharge of the battery  111 - i  and controls the MOS transistors M 1  and M 2 . The protection IC  113 - i  includes a reference voltage generation circuit  211 , an overcharge detection circuit  212 , and an over-discharge detection circuit  213 . The voltage from which the noise component is removed by the filter circuit  112 - i  is applied from the battery  111 - i  to terminals T 11  and T 12  of the protection IC  113 - i.    
         [0000]     (Reference Voltage Generation Circuit  211 )  
         [0046]     The reference voltage generation circuit  211  includes a current source  221  and a constant voltage diode Dz. The reference voltage generation circuit  211  is connected between the terminals T 11  and T 12 , and generates a reference voltage Vref from the voltage across the battery  111 - i . The reference voltage Vref generated in the reference voltage generation circuit  211  is supplied to an overcharge detection circuit  212  and an over-discharged detection circuit  213 .  
         [0000]     (Overcharge Detection Circuit  212 )  
         [0047]      FIG. 4  is a circuit diagram of the overcharge detection circuit  212 .  
         [0048]     The overcharge detection circuit  212  includes a comparator  231 , a delay circuit  232 , current sources  233  and  234 , resistances R 21  and R 22 , and MOS transistors M 11  through M 19 .  
         [0049]     The resistances R 21  and R 22  are connected in series between the terminals T 11  and T 12 , divide the voltage applied between the terminals T 11  and T 12 , and constitute a dividing circuit for generating a detection voltage Vs. The detection voltage Vs is output from the connection point between the resistances R 21  and R 22 , and is applied to a noninverting input terminal of the comparator  231 . The reference voltage Vref is applied from the reference voltage generation circuit  212  to an inverting input terminal of the comparator  231 .  
         [0050]     The comparator  231  is formed by a hysteresis comparator. When the detection voltage Vs becomes adequately higher than the reference voltage Vref, the output of the comparator  231  becomes high level. When the detection voltage Vs becomes adequately lower than the reference voltage Vref, the output of the comparator  231  becomes low level.  
         [0051]     The output of the comparator  231  is supplied to the delay circuit  232 . The delay circuit  232  delays and outputs the supplied output of the comparator  231 .  
         [0052]     A terminal T 15  is connected to the terminal T 12  via the current source  233 . A current is supplied to the terminal T 15  from outside. When the current supplied to the terminal T 15  is large, the potential of the connection point between the terminal T 15  and the current source  233  becomes high level. When the current supplied to the terminal T 15  is small, the potential of the connection point between the terminal T 15  and the current source  233  becomes low level.  
         [0053]     The MOS transistors M 11  through M 14  constitute a NOR gate, and output NOR logic between the output of the delay circuit  232  and the potential of the connection point between the terminal T 15  and the current source  233 . In addition, the MOS transistors M 15  and M 16  constitute an inverter that inverts the output of the NOR gate constituted by the MOS transistors M 11  through M 14 . Further, the MOS transistor M 17  and the current source  234  constitute an output circuit, and serve as an output stage of the inverter constituted by the MOS transistors M 15  and M 16 .  
         [0054]     Additionally, the MOS transistors M 18  and M 19  constitute a current mirror circuit, and return and output from the terminal T 13  the output of the output circuit constituted by the MOS transistor M 17  and the current source  234 .  
         [0055]     Next, a description is given of an operation of the overcharge detection circuit  212 .  
         [0056]     When the battery  111 - i  is overcharged and the detection voltage Vs becomes higher than the reference voltage Vref, the output of the comparator  231  becomes high level. When the output of the comparator  231  becomes high level, the output of the delay circuit  232  becomes high level after being delayed by the delay circuit  232  for a predetermined time interval.  
         [0057]     When the output of the delay circuit  232  becomes high level, the output of the NOR gate constituted by the MOS transistors M 11  through M 14  becomes low level, irrespective of the state of the terminal T 15 . When the output of the NOR gate constituted by the MOS transistors M 11  through M 14  becomes low level, the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level.  
         [0058]     When the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level, the MOS transistor M 17 , constituting the output circuit together with the current source  234 , is turned OFF, and current is drawn from the current mirror circuit constituted by the MOS transistors M 18  and M 19 . Thereby, a current is output to outside from the terminal T 13 .  
         [0059]     In the aforementioned manner, it is possible to detect the overcharged state of the battery  111 - i  connected between the terminals T 11  and T 12 , and to reflect the detected overcharged state to the terminal T 13 .  
         [0060]     In addition, when current is supplied to the terminal T 15  from outside, the potential of the connection point between the terminal T 15  and the current source  233  becomes high level. When the potential of the connection point between the terminal T 15  and the current source  233  becomes high level, the output of the NOR gate, which is constituted by the MOS transistors M 11  through M 14 , becomes low level, irrespective of the output of the delay circuit  232 . When the output of the NOR gate constituted by the MOS transistors M 11  through M 14  becomes low level, the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level.  
         [0061]     When the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level, the MOS transistor M 17 , constituting the output circuit together with the current source  234 , is turned OFF, and current is drawn from the current mirror circuit constituted by the MOS transistors M 18  and M 19 . Thereby, current is output to outside from the terminal T 13 .  
         [0062]     In the aforementioned manner, it is possible to reflect the state of the terminal T 15  to the terminal T 13 .  
         [0000]     (Over-Discharge Detection Circuit  213 )  
         [0063]     Next, a description is given of the over-discharge discharge detection circuit  213 .  
         [0064]      FIG. 5  is a circuit diagram of the over-discharge detection circuit  213 . In  FIG. 5 , those parts that are the same as those corresponding parts in  FIG. 4  are designated by the same reference numerals, and a description thereof is omitted.  
         [0065]     The configuration of the over-discharge detection circuit  213  is substantially the same as that of the overcharge detection circuit  212  shown in  FIG. 4 . The over-discharge detection circuit  213  has a structure obtained by, in the overcharge detection circuit  212  shown in  FIG. 4 , connecting the connection point between the resistances R 21  and R 22  to the inverting input terminal of the comparator  231 , and applying the reference voltage generated in the reference voltage generation circuit  211  to the non-inverting input terminal of the comparator  231 .  
         [0066]     Here, a description is given below of an operation of the over-discharge detection circuit  213 .  
         [0067]     When the battery  111 - i  is over-discharged and the detection voltage Vs becomes lower than the reference voltage Vref, the output of the comparator  231  becomes high level. When the output of the comparator  231  becomes high level, the output of the delay circuit  232  becomes high level after being delayed by the delay circuit  232  for a predetermined time interval.  
         [0068]     When the output of the delay circuit  232  becomes high level, the output of the NOR gate, which is constituted by the MOS transistors M 11  through M 14 , becomes low level, irrespective of the state of a terminal T 16 . When the output of the NOR gate constituted by the MOS transistors M 11  through M 14  becomes low level, the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level.  
         [0069]     When the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level, the MOS transistor M 17 , constituting the output circuit together with the current source  234 , is turned OFF, and current is drawn from the current mirror circuit constituted by the MOS transistors M 18  and M 19 . Thereby, current is output to outside from a terminal T 14 .  
         [0070]     In the aforementioned manner, it is possible to detect the over-discharged state of the battery  111 - i  connected between the terminals T 11  and T 12 , and to reflect the detected over-discharged state to the terminal T 14 .  
         [0071]     When current is supplied to the terminal T 16  from outside, the potential of the connection point between the terminal T 16  and the current source  233  becomes high level. When the potential of the connection point between the terminal T 16  and the current source  233  becomes high level, the output of the NOR gate, which is constituted by the MOS transistors M 11  through M 14 , becomes low level, irrespective of the output of the delay circuit  232 . When the output of the NOR gate constituted by the MOS transistors M 11  through M 14  becomes low level, the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level.  
         [0072]     When the output of the inverter constituted by the MOS transistors M 15  and M 16  becomes high level, the MOS transistor M 17 , constituting the output circuit together with the current source  234 , is turned OFF, and current is drawn from the current mirror circuit constituted by the MOS transistors M 18  and M 19 . Thereby, current is output to outside from the terminal T 14 .  
         [0073]     In the aforementioned manner, it is possible to reflect the state of the terminal T 16  to the terminal T 14 .  
         [0074]     When the battery  111 - i  is overcharged or when current is supplied to the terminal T 15  from outside, current is output from the terminal T 13  of the protection IC  113 - i . On the other hand, when the battery  111 - i  is over-discharged or current is supplied to the terminal T 16  from outside, current is output from the terminal T 14  of the protection IC  113 - i.    
         [0075]     On this occasion, the protection IC  113 - i  is driven only by voltage applied to the terminals T 11  and T 12  from the battery  111 - i . Hence, it is only needed that the protection IC  113 - i  withstands as much voltage as is applied from a single battery  111 - i.    
         [0076]     The protection ICs  113 - 1  through  113 - n  are configured such that the terminal T 13  of a protection IC  113 -(i−1), which is a previous stage, is connected to the terminal T 15  of a protection IC  113 - i , which is the subsequent stage. The terminal T 14  of the protection IC  113 -(i−1), which is the previous stage, is connected to the terminal T 16  of the protection IC  113 - i , which is the subsequent stage.  
         [0077]     Further, the terminals T 15  and T 16  of the protection IC  113 - 1 , which is the first stage, are opened. The terminal T 13  of the protection IC  113 - n , which is the last stage, is connected to the drive circuit  114 . The terminal T 14  of the protection IC  113 - n , which is the last stage, is connected to the drive circuit  115 .  
         [0078]      FIG. 6  is a circuit diagram of the drive circuit  114 .  
         [0079]     The drive circuit  114  includes n-channel MOS transistors M 31  and M 32  and resistances R 31  and R 32 . The drain of the n-channel MOS transistor M 31  is connected to the terminal T 1  via the resistance R 32 , the source thereof is connected to the terminal T 2 , and the gate thereof is connected to the terminal T 13  of the protection IC  113 - n , which is the last stage. The resistance R 31  is connected between the gate of the n-channel MOS transistor M 31  and the terminal T 2 . The source and drain of the n-channel MOS transistor M 32  are connected between the gate of the MOS transistor M 2  and the terminal T 2 , and the gate thereof is connected to the connection point between the resistance R 32  and the drain of the MOS transistor M 31 .  
         [0080]     In the drive circuit  114 , when at least one battery  111 - i  of the batteries  111 - 1  through  111 - n  is overcharged and current is output from the terminal T 13  of the protection IC  113 - n , which is the last stage, current flows to the resistance R 31  and the gate of the MOS transistor M 31  becomes high level. When the gate of the MOS transistor M 31  becomes high level, the MOS transistor M 31  is turned ON. When the MOS transistor M 31  is turned ON, the gate of the MOS transistor M 32  becomes low level.  
         [0081]     When the gate of the MOS transistor M 32  becomes low level, the MOS transistor M 32  is turned OFF. When the MOS transistor M 32  is turned OFF, the drain potential of the MOS transistor M 32  becomes high level. Thereby, the gate of the MOS transistor M 2  becomes high level. Since the MOS transistor M 2  is a p-channel MOS transistor, when the gate becomes high level, the MOS transistor M 2  is turned OFF, and connection between the terminal T 11  and the battery  111 - 1  is disconnected. Thereby, charging of the batteries  111 - 1  through  111 - i  is stopped.  
         [0082]     Since the configuration of the drive circuit  115  is the same as that of the drive circuit  114  shown in  FIG. 6 , a description thereof is omitted. When current is supplied from the terminal T 14  of the protection IC  113 - n , which is the last stage, that is, over-discharge occurs, the drive circuit  115  turns OFF the MOS transistor Ml. Thereby, discharging of the batteries  111 - 1  through  111 - n  is stopped.  
         [0083]     Additionally, in this embodiment, the description has been given of the configuration in which the protection ICs  113 - 1  through  113 - n  are sequentially connected to each other such that the terminals T 13  and T 14  of a previous stage are connected to the terminals T 15  and T 16  of the subsequent stage, respectively, in order to protect the directly connected batteries  111 - 1  through  111 - n . However, the protection IC according to this embodiment may be used independently.  
         [0084]      FIG. 7  is a circuit diagram of a battery protection system  200  according to a variation of the above-mentioned embodiment. Here, it is assumed that the protection IC is used independently. In  FIG. 7 , those parts that are the same as those corresponding parts in  FIG. 2  are designated by the same reference numerals, and a description thereof is omitted.  
         [0085]     The battery protection system  200  is a system for protecting a single battery  111  with a protection IC  113 . The terminals T 11  and T 12  of the protection IC  113  are connected to respective ends of the battery  111  via a filter circuit  112 . In addition, the terminal T 13  of the protection IC  113  is connected to the MOS transistor M 2  via the drive circuit  114 , and the terminal T 14  of the protection IC  113  is connected to the MOS transistor M 1  via the drive circuit  115 . Further, the terminals T 15  and T 16  of the protection IC  113  are opened.  
         [0086]     The protection IC  113  detects the voltage between the terminals T 11  and T 12  so as to detect an overcharged state or over-discharging state of the battery  111 , and controls the MOS transistors M 1  and M 2 , thereby protecting the battery  111  from overcharge and over-discharge.  
         [0087]     As mentioned above, according to this variation, it is possible to use the protection IC  113  for protecting the single battery  111 .  
         [0088]     In the above-mentioned embodiment, the description has been given of the case where the protection IC includes the overcharge detection circuit and the over-discharge detection circuit. However, the circuit shown in  FIG. 3  may further include an over-current detection circuit.  
         [0089]     Additionally, in the above-mentioned embodiment, the terminals T 13  and T 14  of the protection IC  113 -(i−1), which is for protecting a battery  11 -(i−1) arranged at a position of a higher potential, are connected to the terminals T 15  and T 16  of the protection IC  113 -(i−1) for a battery  111 - i  arranged at a position of a subsequently higher potential. However, since it is unnecessary for the protection IC of this embodiment to perform level shifting or the like, the terminals T 13  and T 14  of a protection IC  113 - i  may be connected to the terminals T 15  and T 16  of another protection IC  113 - j , the terminals T 13  and T 14  of a protection IC of the first stage may be opened, and the terminals T 15  and T 16  of a protection IC of the last stage may be connected to the drive circuits  114  and  115 , respectively. It is unnecessary to consider the potentials of batteries  111 - i  and  111 - j , which are being monitored. It should be noted that the protection IC  113 - j  represents an arbitrary one of the protection ICs  113 - 1  through  113 - n , other than the protection IC  113 - i.    
         [0090]     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.  
         [0091]     The present application is based on Japanese Priority Application No. 2004-134319 filed on Apr. 28, 2004, the entire contents of which are hereby incorporated by reference.