Abstract:
Provided is a battery state monitoring circuit which is capable of preventing a discharge leak current from a battery so as to eliminate a load conventionally imposed on a user, including: a battery state detector circuit that detects a state of the battery based on a voltage of the battery; a transmitting terminal that transmits battery state information indicative of the state of the battery to an outside; a receiving terminal that receives battery state information of another battery from the outside; a transistor that is used for transmitting the battery state information, and has any one of two terminals except for a control terminal connected to the transmitting terminal; and a diode that is connected in a direction opposite to a direction of a parasitic diode disposed between the two terminals of the transistor, the diode being disposed between the transmitting terminal and one terminal of the transistor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery state monitoring circuit that monitors a state of a battery, and a battery device that is equipped with a plurality of the battery state monitoring circuits. 
     2. Description of the Related Art 
     For example, JP 2005-117789 A discloses a protective IC that monitors voltages of a plurality of batteries that are connected in series with each other.  FIG. 15A  shows an example of the protective IC that is disclosed in JP 2005-117780 A. Referring to  FIG. 15A , reference numbers  31   a ,  31   b , and  31   c  denote protective ICs, respectively. The protective IC  31   a  monitors the voltages of batteries  1   a  to  1   c , the protective IC  31   b  monitors the voltages of batteries  1   d  to  1   f , and the protective IC  31   c  monitors the voltages of batteries  1   g  to  1   i , respectively. In a normal state, that is, when the voltages of the batteries  1   a  to  1   i  are not abnormal, because all FETs  51 ,  53 , and  55  of the respective protective ICs  31   a ,  31   b , and  31   c  are on, a current flows through a resistor  81 , and a monitor output terminal  42  becomes at high level. On the other hand, for example, when the voltage of any one of the batteries  1   a  to  1   c  becomes overvoltage (overcharged state), a signal of high level is output from an overvoltage detector circuit  34   a ′ that is disposed in the protective IC  31   a  with the results that an FET  73  is turned on, and an FET  75  is turned on. In this situation, because the FET  51  is turned off, no current flows in the resistor  81 , and the monitor output terminal  42  becomes at low level. The same is applied to overdischarge detection. 
     As described above, when the voltage of any one of the batteries  1   a  to  1   c  becomes overvoltage, the monitor output terminal  42  becomes at low level because the FET  73  is turned on, the FET  75  is turned on, and the FET  51  is turned off. However, a parasitic diode having an anode terminal connected to a drain terminal of the FET  51  and a cathode terminal connected to a source terminal of the FET  51  exists between the drain terminal and a gate terminal of the FET  51 . Therefore, when a load is connected between external terminals  41  and  44  in the above state, a current path is formed as shown in  FIG. 15B , which leads to such a problem that electricity is discharged from the batteries  1   d  to  1   i  to generate discharge leak current. 
     The voltages of the batteries  1   d  to  1   i  are decreased due to an influence of the above discharge leak current, but the other batteries  1   a  to  1   c  have the high voltage close to the overvoltage. As a result, the voltage balance of the batteries  1   a  to  1   i  is disrupted. A state in which the voltage balance is disrupted is advanced so that the batteries  1   a  to  1   c  become voltages close to the overvoltage, and the batteries  1   d  to  1   i  become voltages close to overdischarge. As a result, because the overvoltage is detected by small charge, charging cannot be conducted. Also, because the overdischarge is detected by slightly using an application program, the batteries cannot be used. Such batteries are exchanged with fresh batteries. However, because the phenomenon of the discharge leak current is repeated so far as the conventional protective IC is used, the conventional protective IC not only causes inconvenience for a user, but also causes a large load such as costs and time required for battery replacement. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide a battery state monitoring circuit and a battery device which are capable of preventing the discharge leak current from the battery so as to eliminate the load conventionally imposed on the user. 
     In order to achieve the above-mentioned object, as means for solving the above-mentioned problems, the present invention provides a battery state monitoring circuit, including: a battery state detector circuit that detects a state of a battery based on a voltage of the battery; a transmitting terminal that transmits battery state information indicative of the state of the battery to an outside; a receiving terminal that receives battery state information of another battery from the outside; a transistor that is used for transmitting the battery state information, and has any one of two terminals except for a control terminal connected to the transmitting terminal; and a diode that is connected in a direction opposite to a direction of a parasitic diode disposed between the two terminals of the transistor, the diode being disposed between the transmitting terminal and one terminal of the transistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a circuit configuration diagram showing a battery device according to a first embodiment of the present invention; 
         FIG. 2  is an explanatory diagram showing a discharge leak current preventing principle in the battery device according to the first embodiment of the present invention; 
         FIG. 3  is a circuit configuration diagram showing a battery device according to a second embodiment of the present invention; 
         FIG. 4  is an explanatory diagram showing a discharge leak current preventing principle in the battery device according to the second embodiment of the present invention; 
         FIG. 5  is a circuit configuration diagram showing a battery device according to a third embodiment of the present invention; 
         FIG. 6  is a circuit configuration diagram showing a battery device according to a fourth embodiment of the present invention; 
         FIG. 7  is a circuit configuration diagram showing a battery device according to a fifth embodiment of the present invention; 
         FIG. 8  is a circuit configuration diagram showing a battery device according to a sixth embodiment of the present invention; 
         FIG. 9  is a circuit configuration diagram showing a battery device according to a seventh embodiment of the present invention; 
         FIG. 10  is a circuit configuration diagram showing a battery device according to an eighth embodiment of the present invention; 
         FIG. 11  is a circuit configuration diagram showing a battery device according to a ninth embodiment of the present invention; 
         FIG. 12  is a circuit configuration diagram showing a battery device according to a tenth embodiment of the present invention; 
         FIG. 13  is a circuit configuration diagram showing a battery device according to an eleventh embodiment of the present invention; 
         FIG. 14  is a circuit configuration diagram showing a battery device according to a twelfth embodiment of the present invention; and 
         FIG. 15  is an explanatory diagram showing a conventional technology. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a description will be given of embodiments of the present invention with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a circuit configuration diagram showing a battery device according to a first embodiment. As shown in  FIG. 1 , the battery device according to the first embodiment includes n batteries BT 1  to BT n , that are connected in series, n switches (cell balance switch circuits) SW 1  to SW n  which are connected in parallel with each of the batteries Bt 1  to BT n , n battery state monitoring circuits BM 1  to BM n  that are disposed in correspondence with the respective batteries BT 1  to BT n , individually, a first transistor (charging p-channel transistor)  10 , a second transistor (discharging p-channel transistor)  11 , a first resistive element (first bias resistive element)  20 , a second resistive element (second bias resistive element)  21 , a first external terminal  30 , and a second external terminal  31 . 
     The battery state monitoring circuit BM 1  includes an overcharge detector circuit A 1 , a first NOR circuit B 1 , a first output transistor C 1 , a diode Do 1 , a first inverter D 1 , a second inverter E 1 , a first current source F 1 , an overdischarge detector circuit G 1 , a second NOR circuit H 1 , a second output transistor I 1 , a third inverter J 1 , a fourth inverter K 1 , a second current source L 1 , a cell balance circuit M 1 , a first voltage monitor terminal PA 1 , a second voltage monitor terminal PB 1 , a first transmitting terminal PC 1 , a second transmitting terminal PD 1 , a first receiving terminal PE 1 , a second receiving terminal PF 1 , and a control terminal PG 1 . The battery state monitoring circuit BM 1  having the above components is configured as an IC (semiconductor device) of one chip. 
     The other battery state monitoring circuits BM 2  to BM n  have the same components as those of the battery state monitoring circuit BM 1 , and therefore are shown with a change in only symbols. For example, the symbol of the overcharge detector circuit in the battery state monitoring circuit BM 2  is A 2  whereas the symbol of the overcharge detector circuit in the battery state monitoring circuit BM n  is A n . The same is applied to other components. 
     Since all of the battery state monitoring circuits BM 1  to BM n  are identical in circuit configuration with each other as described above, the battery state monitoring circuit BM 1  corresponding to the battery BT 1  will be representatively described below. 
     In the battery state monitoring circuit BM 1 , the first voltage monitor terminal PA 1  is connected to a positive terminal of the battery BT 1  and one terminal of the switch SW 1 . Also, the first voltage monitor terminal PA 1  is connected to a positive side common power source wire within the battery state monitoring circuit BM 1 . The second voltage monitor terminal PB 1  is connected to a negative terminal of the battery BT 1  and another terminal of the switch SW 1 . Also, the second voltage monitor terminal PB 1  is connected to a negative side common power source wire within the battery state monitoring circuit BM 1 . In the following description, the positive side common power source wire is VDD 1  and the negative side common power source wire is VSS 1  within the battery state monitoring circuit BM 1 , and the positive side common power source wire is VDD 2  and the negative side common power source wire is VSS 2  within the battery state monitoring circuit BM 2 . In the same manner, the positive side common power source wire is VDD n  and the negative side common power source wire is VSS n  within the battery state monitoring circuit BM n . 
     The overcharge detector circuit A 1  has one end connected to the first voltage monitor terminal PA 1 , and another end connected to the second voltage monitor terminal PB 1 . The overcharge detector circuit A 1  detects a voltage between the first voltage monitor terminal PA 1  and the second voltage monitor terminal PB 1  (that is, voltage of battery BT 1 ). When the voltage of the battery BT 1  is equal to or higher than an overcharge voltage, the overcharge detector circuit A 1  outputs an overcharge detection signal of high level to one input terminal of the first NOR circuit B 1 . Also, when the voltage of the battery BT 1  is lower than the overcharge voltage, the overcharge detector circuit A 1  outputs an overcharge detection signal of low level to the first NOR circuit B 1 . Here, the overcharge voltage is an upper limit chargeable voltage. The overcharge detector circuit A 1  has a function of stopping the operation when the overdischarge detection signal of high level is input to the overcharge detector circuit A 1  from the overdischarge detector circuit G 1 . 
     To the first NOR circuit B 1 , the above overcharge detection signal and an output signal of the first inverter D 1  are input, and the first NOR circuit B 1  outputs a negative OR signal of both of those signals to a gate terminal of the first output transistor C 1 . The first output transistor C 1  is an n-channel type metal oxide semiconductor (MOS) transistor. The first output transistor C 1  has the gate terminal connected to an output terminal of the first NOR circuit B 1 , a drain terminal connected to a cathode terminal of the diode Do 1 , and a source terminal connected to the VSS 1 . The diode Do 1    1  is a discharge leak current prevention diode. The diode Do 1  has the cathode terminal connected to the drain terminal of the first output transistor C 1 , and an anode terminal connected to the first transmitting terminal PC 1 . 
     The first inverter D 1  outputs a logical inversion signal of an output signal from the second inverter E 1  to the first NOR circuit B 1 . The second inverter E 1  has an input terminal connected to the first receiving terminal PE 1  and an output terminal of the first current source F 1 , and outputs a logical inversion signal of an input signal to an input terminal to the first inverter D 1 . The first current source F 1  is a current source having an input terminal connected to the VDD 1 , and the output terminal connected to the input terminal of the second inverter E 1  and the first receiving terminal PE 1 . 
     The overdischarge detector circuit G 1  has one end connected to the first voltage monitor terminal PA 1 , and another end connected to the second voltage monitor terminal PB 1 . The overdischarge detector circuit G 1  detects a voltage between the first voltage monitor terminal PA 1  and the second voltage monitor terminal PB 1  (that is, voltage of battery BT 1 ). When the voltage of the battery BT 1  is lower than an overdischarge voltage, the overdischarge detector circuit G 1  outputs an overdischarge detection signal of high level to one input terminal of the second NOR circuit H 1 , the overcharge detector circuit A 1 , and the cell balance circuit M 1 . Also, when the voltage of the battery BT 1  is equal to or higher than the overdischarge voltage, the overdischarge detector circuit G 1  outputs an overdischarge detection signal of low level. Here, the overdischarge voltage is a lower limit dischargeable voltage. 
     To the second NOR circuit H 1 , the above overdischarge detection signal and an output signal of the third inverter J 1  are input, and the second NOR circuit H 1  outputs a negative OR signal of both of those signals to a gate terminal of the second output transistor I 1 . The second output transistor I 1  is an n-channel type MOS transistor. The second output transistor I 1  has the gate terminal connected to an output terminal of the second NOR circuit H 1 , a drain terminal connected to the second transmitting terminal PD 1 , and a source terminal connected to the VSS 1 . 
     The third inverter J 1  outputs a logical inversion signal of an output signal from the fourth inverter K 1  to the second NOR circuit H 1 . The fourth inverter K 1  has an input terminal connected to the second receiving terminal PF 1  and an output terminal of the second current source L 1 , and outputs a logical inversion signal of an input signal to the input terminal to the fourth inverter K 1 . The second current source L 1  is a current source having an input terminal connected to the VDD 1 , and the output terminal connected to the input terminal of the fourth inverter L 1  and the second receiving terminal PF 1 . 
     The cell balance circuit M 1  has one end connected to the first voltage monitor terminal PA 1 , and another end connected to the second voltage monitor terminal PB 1 . The cell balance circuit M 1  detects a voltage between the first voltage monitor terminal PA 1  and the second voltage monitor terminal PB 1  (that is, voltage of battery BT 1 ). When the voltage of the battery BT 1  is equal to or higher than a cell balance voltage, the cell balance circuit M 1  outputs a cell balance signal to the switch SW 1  through the control terminal PG 1 . Also, when the voltage of the battery BT 1  is lower than the cell balance voltage, the cell balance circuit M 1  outputs a cell balance signal of low level to the switch SW 1  through the control terminal PG 1 . Here, the cell balance voltage is a voltage that is equal to or lower than the overcharge voltage in the case in which the battery BT 1  comes to a state close to the overcharged state (voltage in the case in which voltage of battery BT 1  is adjusted to voltages of other batteries to start to balance). The cell balance circuit M 1  has a function of stopping the operation when the overdischarge detection signal of high level is input to the cell balance circuit M 1  from the overdischarge detector circuit G 1 . 
     The first transmitting terminal PC 1  is connected to a gate terminal of the first transistor  10  and one end of the first resistive element  20 . The second transmitting terminal PD 1  is connected to a gate terminal of the second transistor  11  and one end of the second resistive element  21 . The first receiving terminal PE 1  is connected to a first transmitting terminal PC 2  of the battery state monitoring circuit BM 2 . The second receiving terminal PF 1  is connected to a second transmitting terminal PD 2  of the battery state monitoring circuit BM 2 . 
     Also, a first receiving terminal PE 2  of the battery state monitoring circuit BM 2  is connected to a first transmitting terminal PC 3  of the battery state monitoring circuit BM 3 , and a second receiving terminal PF 2  of the battery state monitoring circuit BM 2  is connected to a second transmitting terminal PD 3  of the battery state monitoring circuit BM 3 . The same is applied to the battery state monitoring circuits BM 3  to BM n , and the first receiving terminal of the battery state monitoring circuit on an upstream side (battery BT 1  side) is connected to the first transmitting terminal of the battery state monitoring circuit on a downstream side (battery BT n  side). The second receiving terminal of the battery state monitoring circuit on the upstream side is connected to the second transmitting terminal of the battery state monitoring circuit on the downstream side. A first receiving terminal PE n  and a second receiving terminal PF n  of the battery state monitoring circuit BM n  which is the most downstream side are connected to a negative terminal of the battery BT n . 
     The switch SW 1  is connected in parallel with the battery BT 1 , and changes over between the connection and the disconnection of the two terminals (that is, positive terminal and negative terminal of battery BT 1 ) according to the cell balance signal that is input to the switch SW 1  through the control terminal PG 1 . The switch SW 1  is turned on, that is, changes over the two terminals to the connection state when the cell balance signal is input. The same is applied to the other switches SW 2  to SW n . 
     The first transistor  10  is a p-channel type MOS transistor. The first transistor  10  has the gate terminal connected to the first transmitting terminal PC 1  of the battery state monitoring circuit BM 1  and the one end of the first resistive element  20 . The first transistor  10  also has a drain terminal connected to a drain terminal of the second transistor  11 , and a source terminal connected to another terminal of the first resistive element  20  and the first external terminal  30 . The second transistor  11  is a p-channel type MOS transistor. The second transistor  11  has the gate terminal connected to the second transmitting terminal PD 1  of the battery state monitoring circuit BM 1  and the one end of the second resistive element  21 . The second transistor  11  also has the drain terminal connected to the drain terminal of the first transistor  10 , and a source terminal connected to another terminal of the second resistive element  21  and the positive terminal of the battery BT 1 . On the other hand, the second external terminal  31  is connected to the negative terminal of the battery BT n  on the most downstream side. 
     In the battery device configured as described above, a load or a charger is connected between the first external terminal  30  and the second external terminal  31  to conduct discharging or charging. 
     Subsequently, a description will be given of the operation of the battery device according to the first embodiment, which is configured as described above. 
     (Normal State) 
     First, a description will be given of a normal state, that is, a case in which all the voltages of the batteries BT 1  to BT n  are lower than the overcharge voltage, and equal to or higher than the overdischarge voltage. In the normal state thus defined, the overcharge detector circuit A 1  of the battery state monitoring circuit BM 1  outputs the overcharge detection signal of low level to the first NOR circuit B 1 . 
     In this situation, a first output transistor C 2  of the battery state monitoring circuit BM 2  is on (the reason will be described later). As a result, the input terminal of the second inverter E 1  of the battery state monitoring circuit BM 1  is at low level, and the output signal of low level is output from the first inverter D 1  to the first NOR circuit B 1 . Because, to the first NOR circuit B 1 , the overcharge detection signal of low level and the output signal of low level of the first inverter D 1  are input, the first NOR circuit B 1  outputs the negative OR signal of high level to the gate terminal of the first output transistor C 1 . As a result, because the first output transistor C 1  is turned on, the first transmitting terminal PC 1  becomes at low level, and the first transistor  10  is turned on. 
     Now, the reason why the first output transistor C 2  of the battery state monitoring circuit BM 2  is on will be described below. Because the first receiving terminal PE n  of the battery state monitoring circuit BM n  on the most downstream side is connected to the negative terminal of the battery BT n , an input terminal of a second inverter E n  is always held at low level. Accordingly, a first inverter D n  always outputs the output signal of low level to a first NOR circuit B n , and the overcharge detector circuit A n  outputs the overcharge detection signal of low level to the first NOR circuit B n . With the above arrangement, the first NOR circuit B n  outputs the negative OR signal of high level to a gate terminal of a first output transistor C n , and the first output transistor C n  of the battery state monitoring circuit BM n  is turned on. 
     As a result, an input terminal of a second inverter E n-1  in the battery state monitoring circuit BM n-1  becomes at low level, and the output signal of low level is output to a first NOR circuit B n-1  from a first inverter D n-1 . On the other hand, since an overcharge detector circuit A n-1  outputs the overcharge detection signal of low level to the first NOR circuit B n-1 , the first NOR circuit B n-1  outputs the negative OR signal of high level to a gate terminal of a first output transistor C n-1 . As a result, the first output transistor C n-1  of the battery state monitoring circuit BM n-1  is turned on. 
     The above operation is repeated in the upstream side battery state monitoring circuit and the downstream side battery state monitoring circuit, and the first output transistor C 2  of the battery state monitoring circuit BM 2  is turned on. 
     Also, in the above normal state, the overdischarge detector circuit G 1  of the battery state monitoring circuit BM 1  outputs the overdischarge detection signal of low level to the second NOR circuit H 1 . In this situation, because a second output transistor I 2  of the battery state monitoring circuit BM 2  is also on, the input terminal of the fourth inverter K 1  of the battery state monitoring circuit BM 1  becomes at low level, and the output signal of low level is output to the second NOR circuit H 1  from the third inverter J 1 . Because, to the second NOR circuit H 1 , the overdischarge detection signal of low level and the output signal of low level of the third inverter J 1  are input, the second NOR circuit H 1  outputs the negative OR signal of high level to the gate terminal of the second output transistor I 1 . As a result, because the second output transistor I 1  is turned on, the second transmitting terminal PD 1  becomes at low level, and the second transistor  11  is turned on. 
     As described above, in the normal state, because the first transistor  10  and the second transistor  11  are turned on, the battery device is chargeable and dischargeable. 
     (Overcharged State) 
     Subsequently, a description will be given of an overcharged state, that is, a case in which a charger is connected between the first external terminal  30  and the second external terminal  31  to charge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes equal to or higher than the overcharge voltage. In the following description, it is assumed that the voltage of the battery BT 2  is equal to or higher than the overcharge voltage. 
     In this case, the overcharge detector circuit A 2  of the battery state monitoring circuit BM 2  outputs the overcharge detection signal of high level to a first NOR circuit B 2 . In this situation, because the output signal of low level is output from a first inverter D 2 , the first NOR circuit B 2  outputs the negative OR signal of low level to a gate terminal of the first output transistor C 2 . As a result, the first output transistor C 2  is turned off. 
     That is, the input terminal of the second inverter E 1  is pulled up to high level by means of the first current source F 1  and the output signal of high level is output to the first NOR circuit B 1  from the first inverter D 1 . On the other hand, because the overcharge detector circuit A 1  outputs the overcharge detection signal of low level to the first NOR circuit B 1 , the first NOR circuit B 1  outputs the negative OR signal of low level to the gate terminal of the first output transistor C 1 . As a result, the first output transistor C 1  is turned off. 
     As described above, when the first output transistor C 1  is turned off, the gate terminal of the first transistor  10  becomes at high level by means of the first resistive element  20 , and the first transistor  10  is turned off. As a result, the charging from the charger is prohibited. 
     In the above description, it is assumed that the voltage of the battery BT 2  is equal to or higher than the overcharge voltage. The same is applied to a case in which the voltages of the other batteries are equal to or higher than the overcharge voltage. That is, a fact that the overcharged state occurs is communicated from the battery state monitoring circuit corresponding to the battery that has become in the overcharged state to the upstream side battery state monitoring circuit, and the communication reaches the most upstream side battery state monitoring circuit BM 1 . As a result, the first transistor  10  is turned off to prohibit the charging from the charger. 
     (Overdischarged State) 
     Subsequently, a description will be given of an overdischarged state, that is, a case in which a load is connected between the first external terminal  30  and the second external terminal  31  to discharge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes lower than the overdischarge voltage. In the following description, it is assumed that the voltage of the battery BT 2  is lower than the overdischarge voltage. 
     In this case, an overdischarge detector circuit G 2  of the battery state monitoring circuit BM 2  outputs the overdischarge detection signal of high level to a second NOR circuit H 2 . In this situation, because the output signal of low level is output from a third inverter J 2 , the second NOR circuit H 2  outputs the negative OR signal of low level to a gate terminal of the second output transistor I 2 . As a result, the second output transistor I 2  is turned off. 
     That is, the input terminal of the fourth inverter K 1  is pulled up to high level by means of the second current source L 1 , and the output signal of high level is output to the second NOR circuit H 1  from the third inverter J 1 . On the other hand, because the overdischarge detector circuit G 1  outputs the overdischarge detection signal of low level to the second NOR circuit H 1 , the second NOR circuit H 1  outputs the negative OR signal of low level to the gate terminal of the second output transistor I 1 . As a result, the second output transistor I 1  is turned off. 
     As described above, when the second output transistor I 1  is turned off, the gate terminal of the second transistor  11  becomes at high level by means of the second resistive element  21 , and the second transistor  11  is turned off. As a result, the discharging to the load is prohibited. 
     Also, in the above overdischarge state, the overdischarge detector circuit G 2  that has detected the overdischarged state outputs the overdischarge detection signal of high level to the overcharge detector circuit A 2  and a cell balance circuit M 2 . With the above configuration, because the overcharge detector circuit A 2  and the cell balance circuit M 2  stop the operation, it is possible to reduce the power consumption. Also, a first voltage monitor terminal PA 2  also functions as a VDD power source terminal of the battery state monitoring circuit BM 2 , and the battery state monitoring circuit BM 2  receives a power from the battery BT 2 . As a result, the voltage of the overdischarged battery BT 2  becomes low, and the power consumption of the battery state monitoring circuit BM 2  is reduced as much. 
     In this example, when the characteristic variation occurs in the respective batteries to decrease the voltage of the battery BT 2  earlier than the voltages of the other batteries during discharging, the overdischarge detector circuit G 2  of the battery state monitoring circuit BM 2  outputs the overdischarge detection signal earlier than other battery state monitoring circuits. Then, the second transistor  11  is turned off to prohibit the discharging. In this situation, in the battery state monitoring circuit BM 2 , the power consumption is reduced more than those of the other battery state monitoring circuits. The battery BT 2  is lower than the other batteries in discharge speed as much as the power consumption is reduced, and the other batteries discharge electricity in the usual manner. Therefore, since the discharge speed of the overdischarged battery BT 2  becomes low, the battery device is capable of conforming the voltages of the respective batteries to each other (taking cell balance). 
     In the above description, it is assumed that the voltage of the battery BT 2  is lower than the overdischarge voltage. The same is applied to a case in which the voltages of the other batteries are lower than the overdischarge voltage. That is, a fact that the overdischarged state occurs is communicated from the battery state monitoring circuit corresponding to the battery that has become in the overdischarged state to the upstream side battery state monitoring circuit, and the communication reaches the most upstream side battery state monitoring circuit BM 1 . As a result, the second transistor  11  is turned off to prohibit the discharging to the load. 
     (Cell Balance State) 
     Subsequently, a description will be given of a cell balance state, that is, a case in which a charger is connected between the first external terminal  30  and the second external terminal  31  to charge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes equal to or higher than the cell balance voltage. In the following description, it is assumed that the voltage of the battery BT 2  is equal to or higher than the cell balance voltage. 
     In this case, the cell balance circuit M 2  of the battery state monitoring circuit BM 2  outputs the cell balance signal to the switch SW 2  through a control terminal PG 2 . With the above configuration, the switch SW 2  is turned on, and the charged battery BT 2  discharges electricity through the switch SW 2 . 
     In this example, when the characteristic variation occurs in the respective batteries to increase the voltage of the battery BT 2  earlier than the voltages of the other batteries during charging, the battery state monitoring circuit BM 2  outputs the cell balance signal earlier than the other battery state monitoring circuits. Then, the switch SW 2  is turned on earlier than the other switches, and the battery BT 2  is different from the other batteries in change in amount of charge. For example, the battery BT 2  is lower in charging speed than the other batteries, and the other batteries are charged in the usual manner. Alternatively, the battery BT 2  is discharged, and the other batteries are charged in the usual manner. As a result, since the charging speed of the overcharged battery BT 2  becomes low, or since the overcharged battery BT 2  is discharged, the battery device is capable of taking the cell balance. 
     Hereinafter, a description will be given of the reason why the discharge leak current can be prevented with the provision of the diode Do 1  in the battery state monitoring circuit BM 1  on the premise of the above operation.  FIG. 2  shows the circuit configuration of the battery device in which no diode Do 1  is provided. For example, in  FIG. 2 , it is assumed that the battery BT 1  is overdischarged during the discharging to the load, and the second transistor  11  is turned off. In this case, the first output transistor C 1  of the most upstream side battery state monitoring circuit BM 1  becomes off. However, because a parasitic diode having a cathode terminal on the drain side and an anode terminal on the source side exists between the drain terminal and the gate terminal of the first output transistor C 1 , a current path is formed as shown in  FIG. 2 . As a result, the electric discharge of the batteries BT 2  to BT n  does not stop, thereby causing the discharge leak current to occur. On the other hand, according to the battery state monitoring circuit BM 1  of the first embodiment, because the diode Do 1  of a direction opposite to the parasitic diode of the first output transistor C 1  is provided, it is possible to prevent the discharge leak current shown in  FIG. 2  from occurring. 
     As described above, in the battery device according to the first embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user, such as the costs and time required for battery exchange. 
     Second Embodiment 
     Subsequently, a description will be given of a battery device according to a second embodiment. In the above first embodiment, the description is given of a case in which the n-channel type MOS transistors are used as the first output transistor and the second output transistor in the battery state monitoring circuit. In contrast, in the second embodiment, a description will be given of a battery device in the case where p-channel type MOS transistors are used as the first output transistor and the second output transistor. 
       FIG. 3  is a circuit configuration diagram showing the battery device according to the second embodiment. In  FIG. 3 , the same components as those of  FIG. 1  are denoted by identical symbols, and their description will be omitted. In order to distinguish from  FIG. 1 , the symbols of the battery state monitoring circuits are BMA 1  to BMA n , the symbol of the first transistor is  12 , the symbol of the second transistor is  13 , the symbol of the first resistive element is  22 , and the symbol of the second resistive element is  23 . Also, since the circuit configurations of those battery state monitoring circuits BMA 1  to BMA n  are identical with each other, the most downstream side battery state monitoring circuit BMA n  will be representatively described below. 
     The battery state monitoring circuit BMA n  according to the second embodiment includes the overcharge detector circuit A n , the first NOR circuit B n , a first inverter Q n , a first output transistor R n , a diode Do n , a second inverter S n , a first current source T n , an overdischarge detector circuit G n , a second NOR circuit H n , a third inverter U n , a second output transistor V n , a fourth inverter W n , a second current source X n , a cell balance circuit M n , a first voltage monitor terminal PA n , a second voltage monitor terminal PB n , a first transmitting terminal PC, a second transmitting terminal PD n , a first receiving terminal PE n , a second receiving terminal PF n , and a control terminal PG n . The battery state monitoring circuit BMA n  having the above components is configured as an IC of one chip. 
     To the first NOR circuit B n , an overcharge detection signal that is output from the overcharge detector circuit A n , and an output signal of the second inverter S n  are input, and the first NOR circuit B n  outputs a negative OR signal of those signals to the first inverter Q n . The first inverter Q n  outputs the logical inversion signal of the negative OR signal that is input from the first NOR circuit B n  to a gate terminal of the first output transistor R n . The first output transistor R n  is a p-channel type MOS transistor. The first output transistor R n  has the gate terminal connected to an output terminal of the first inverter Q n , a drain terminal connected to an anode terminal of the diode Do n , and a source terminal connected to the VDD n . The diode Do n  is a discharge leak current prevention diode, and has the anode terminal connected to the drain terminal of the first output transistor R n , and a cathode terminal connected to the first transmitting terminal PC n . 
     The second inverter S n  has an input terminal connected to the first receiving terminal PE n  and an input terminal of the first current source T n , and outputs the logical inversion signal of the input signal to the input terminal to the first NOR circuit B n . The first current source T n  is a current source that has the input terminal connected to the first receiving terminal PE n  and the input terminal of the second inverter S n , and an output terminal connected to the VSS n . 
     To the second NOR circuit H n , an overdischarge detection signal that is output from the overdischarge detector circuit G n  and the output signal of the fourth inverter W n  are input, and the second NOR circuit H n  outputs a negative OR signal of those signals to the third inverter U n . The third inverter U n  outputs the logical inversion signal of the negative OR signal that is input from the second NOR circuit H n  to a gate terminal of the second output transistor V n . The second output transistor V n  is a p-channel type MOS transistor, and has the gate terminal connected to an output terminal of the third inverter U n , a drain terminal connected to the second transmitting terminal PD n , and a source terminal connected to the VDD n . 
     The fourth inverter W n  has an input terminal connected to the second receiving terminal PF n  and an input terminal of the second current source X n , and outputs the logical inversion signal of the input signal to the input terminal to the second NOR circuit H n . The second current source X n  is a current source that has the input terminal connected to the second receiving terminal PF n  and the input terminal of the fourth inverter W n , and an output terminal connected to the VSS n . 
     The first transmitting terminal PC n  is connected to a gate terminal of the first transistor  12  and one end of the first resistive element  22 . The second transmitting terminal PD n  is connected to a gate terminal of the second transistor  13  and one end of the second resistive element  23 . The first receiving terminal PE n  is connected to a first transmitting terminal PC n-1  of the battery state monitoring circuit BMA n-1 . The second receiving terminal PF n  is connected to a second transmitting terminal PD n-1  of the battery state monitoring circuit BMA n-1 . 
     The same is applied to the other battery state monitoring circuits, and the first receiving terminal of the battery state monitoring circuit on the downstream side (battery BT n  side) is connected to the first transmitting terminal of the battery state monitoring circuit on the upstream side (battery BT 1  side). The second receiving terminal of the battery state monitoring circuit on the downstream side is connected to the second transmitting terminal of the battery state monitoring circuit on the upstream side. The first receiving terminal PE 1  and the second receiving terminal PF 1  of the battery state monitoring circuit BMA 1  which is the most upstream side are connected to the positive terminal of the battery BT 1 . 
     The first transistor  12  is an n-channel type MOS transistor. The first transistor  12  has the gate terminal connected to the first transmitting terminal PC n  of the battery state monitoring circuit BM n  and the one end of the first resistive element  22 . The first transistor  12  also has a drain terminal connected to a drain terminal of the second transistor  13 , and a source terminal connected to another terminal of the first resistive element  22  and the negative terminal of the battery BT n . The second transistor  13  is an n-channel type MOS transistor. The second transistor  13  has the gate terminal connected to the second transmitting terminal PD n  of the battery state monitoring circuit BMA n  and the one end of the second resistive element  23 . The second transistor  13  also has the drain terminal connected to the drain terminal of the second transistor  12 , and a source terminal connected to another terminal of the second resistive element  23  and the second external terminal  31 . On the other hand, the first external terminal  30  is connected to the positive terminal of the battery BT 1  on the most upstream side. 
     Subsequently, a description will be given of the operation of the battery device according to the second embodiment, which is configured as described above. The operation in the cell balance state is identical with that in the first embodiment, and therefore its description will be omitted. 
     (Normal State) 
     First, a description will be given of a normal state, that is, a case in which the voltages of all the batteries BT 1  to BT n  are lower than the overcharge voltage, and equal to or higher than the overdischarge voltage. In the normal state thus defined, the overcharge detector circuit A n  of the battery state monitoring circuit BMA n  outputs the overcharge detection signal of low level to the first NOR circuit B n . 
     In this situation, a first output transistor R n-1  of the battery state monitoring circuit BMA n-1  is on (the reason will be described later). As a result, the input terminal of the second inverter S n  of the battery state monitoring circuit BMA n  becomes at high level, and the output signal of low level is output from the second inverter S n  to the first NOR circuit B n . The first NOR circuit B n  outputs the negative OR signal of high level to the first inverter Q n , and the first inverter Q n  outputs the logical inversion signal of low level to the gate terminal of the first output transistor R n . As a result, because the first output transistor R n  is turned on, the first transmitting terminal PC n  becomes at high level, and the first transistor  12  is turned on. 
     Now, the reason why the first output transistor R n-1  of the battery state monitoring circuit BMA n-1  is on will be described below. Because the first receiving terminal PE 1  of the battery state monitoring circuit BMA 1  on the most upstream side is connected to the positive terminal of the battery BT 1 , an input terminal of a second inverter S 1  is always held at high level. Accordingly, the second inverter S 1  always outputs the output signal of low level to the first NOR circuit B 1 , and the overcharge detector circuit A 1  outputs the overcharge detection signal of low level to the first NOR circuit B 1 . With the above arrangement, the first NOR circuit B 1  outputs the negative OR signal of high level to a first inverter Q 1 , and the first inverter Q 1  outputs the logical inversion signal of low level to a gate terminal of a first output transistor R 1 . As a result, the first output transistor R 1  of the battery state monitoring circuit BMA 1  is turned on. 
     In this situation, an input terminal of a second inverter S 2  in the battery state monitoring circuit BMA 2  that is the downstream side of the battery state monitoring circuit BMA 1  becomes at high level, and the output signal of low level is output from the second inverter S 2  to the first NOR circuit B 2 . Since the overcharge detector circuit A 2  outputs the overcharge detection signal of low level, the first NOR circuit B 2  outputs the negative OR signal of high level to a first inverter Q 2 , and the first inverter Q 2  outputs the logical inversion signal of low level to a gate terminal of a first output transistor R 2 . As a result, the first output transistor R 2  is turned on. 
     The above operation is repeated in the upstream side battery state monitoring circuit and the downstream side battery state monitoring circuit, and the first output transistor R n-1  of the battery state monitoring circuit BMA n-1  is turned on. 
     Also, in the above normal state, the overdischarge detector circuit G of the battery state monitoring circuit BM n  outputs the overdischarge detection signal of low level to the second NOR circuit H n . In this situation, because a second output transistor V n-1  of the battery state monitoring circuit BM n-1  is also on, the input terminal of the fourth inverter W n  in the battery state monitoring circuit BMA n  becomes at high level, and the output signal of low level is output to the second NOR circuit H n  from the fourth inverter W n . The second NOR circuit H n  outputs the negative OR signal of high level to the third inverter U n , and the third inverter U n  outputs the logical inversion signal of low level to the gate terminal of the second output transistor V n . As a result, because the second output transistor V n  is turned on, the second transmitting terminal PD n  becomes at high level, and the second transistor  13  is turned on. 
     As described above, in the normal state, because the first transistor  12  and the second transistor  13  are turned on, the battery device is chargeable and dischargeable. 
     (Overcharged State) 
     Subsequently, a description will be given of an overcharged state, that is, a case in which a charger is connected between the first external terminal  30  and the second external terminal  31  to charge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes equal to or higher than the overcharge voltage. In the following description, it is assumed that the voltage of the battery BT n-1  is equal to or higher than the overcharge voltage. 
     In this case, the overcharge detector circuit A n-1  of the battery state monitoring circuit BMA n-1  outputs the overcharge detection signal of high level to the first NOR circuit B n-1 . In this situation, because the output signal of low level is output from a second inverter S n-1 , the first NOR circuit B n-1  outputs the negative OR signal of low level to a first inverter Q n-1 , and the first inverter Q n-1  outputs the logical inversion signal of high level to a gate terminal of the first output transistor R n-1 . As a result, the first output transistor R n-1  is turned off. 
     That is, the input terminal of the second inverter S n  is pulled down to low level by means of the first current source T n , and the output signal of high level is output to the first NOR circuit B n  from the second inverter S n . On the other hand, because the overcharge detector circuit A n  outputs the overcharge detection signal of low level to the first NOR circuit B n , the first NOR circuit B n  outputs the negative OR signal of low level to the first inverter Q n , and the first inverter Q n  outputs the logical inversion signal of high level to the gate terminal of the first output transistor R n . As a result, the first output transistor R n  is turned off. 
     As described above, when the first output transistor R n  is turned off, the gate terminal of the first transistor  12  becomes at low level by means of the first resistive element  22 , and the first transistor  12  is turned off. As a result, the charging from the charger is prohibited. 
     In the above description, it is assumed that the voltage of the battery BT n-1  is equal to or higher than the overcharge voltage. The same is applied to a case in which the voltages of the other batteries are equal to or higher than the overcharge voltage. That is, a fact that the overcharged state occurs is communicated from the battery state monitoring circuit corresponding to the battery that has become in the overcharged state to the downstream side battery state monitoring circuit, and the communication reaches the most downstream side battery state monitoring circuit BMA n . As a result, the first transistor  12  is turned off to prohibit the charging from the charger. 
     (Overdischarged State) 
     Subsequently, a description will be given of an overdischarged state, that is, a case in which a load is connected between the first external terminal  30  and the second external terminal  31  to discharge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes lower than the overdischarge voltage. In the following description, it is assumed that the voltage of the battery BT n-1  is lower than the overdischarge voltage. 
     In this case, an overdischarge detector circuit G n-1  of the battery state monitoring circuit BMA n-1  outputs the overdischarge detection signal of high level to a second NOR circuit H n-1 . In this situation, because the output signal of low level is output from a fourth inverter W n-1 , the second NOR circuit H n-1  outputs the negative OR signal of low level to a third inverter U n-1 , and the third inverter U n-1  outputs the logical inversion signal of high level to a gate terminal of the second output transistor V n-1 . As a result, the second output transistor V n-1  is turned off. 
     That is, the input terminal of the fourth inverter W n  is pulled down to low level by means of the second current source X n , and the output signal of high level is output to the second NOR circuit H n  from the fourth inverter W n . On the other hand, because the overdischarge detector circuit G n  outputs the overdischarge detection signal of low level to the second NOR circuit H n , the second NOR circuit H n  outputs the negative OR signal of low level to the third inverter U n , and the third inverter U n  outputs the logical inversion signal of high level to the gate terminal of the second output transistor V n . As a result, the second output transistor V n  is turned off. 
     As described above, when the second output transistor V n  is turned off, the gate of the second transistor  13  becomes at low level by means of the second resistive element  23 , and the second transistor  13  is turned off. As a result, the discharging to the load is prohibited. 
     In the above description, it is assumed that the voltage of the battery BT n-1  is lower than the overdischarge voltage. The same is applied to a case in which the voltages of the other batteries are lower than the overdischarge voltage. That is, a fact that the overdischarged state occurs is communicated from the battery state monitoring circuit corresponding to the battery that has become in the overdischarged state to the downstream side battery state monitoring circuit, and the communication reaches the most downstream side battery state monitoring circuit BMA n . As a result, the second transistor  13  is turned off to prohibit the discharging to the load. 
     Hereinafter, a description will be given of the reason why the discharge leak current can be prevented with the provision of the diode Do n  in the battery state monitoring circuit BMA n  on the premise of the above operation.  FIG. 4  shows the circuit configuration of the battery device in which no diode Do n  is provided. For example, in  FIG. 4 , it is assumed that the battery BT n  is overdischarged during the discharging to the load, and the second transistor  13  is turned off. In this case, the first output transistor R n  of the battery state monitoring circuit BMA n  becomes off. However, because a parasitic diode having a cathode terminal on the source side and an anode terminal on the drain side exists between the drain terminal and the gate terminal of the first output transistor R n , a current path is formed as shown in  FIG. 4 . As a result, the electric discharge of the batteries BT 1  to BT n-1  does not stop, thereby causing the discharge leak current to occur. On the other hand, according to the battery state monitoring circuit BMA n  of the second embodiment, because the diode Do n  of a direction opposite to the parasitic diode of the first output transistor R n  is provided, it is possible to prevent the discharge leak current shown in  FIG. 4  from occurring. 
     As described above, in the battery device according to the second embodiment, the occurrence of the discharge leak current can be prevented as in the first embodiment, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user, such as the costs and time required for battery exchange. 
     Third Embodiment 
     Subsequently, a description will be given of a battery device according to a third embodiment.  FIG. 5  is a circuit configuration diagram showing the battery device according to the third embodiment. As shown in the figure, in the third embodiment, two types of diodes are disposed in the battery state monitoring circuit of the first embodiment. That is, when it is assumed that the symbols of the battery state monitoring circuits are BMB 1  to BMB n , the battery state monitoring circuit BMB 1  is newly equipped with a first diode (first clamp diode) Da 1 , a second diode (second clamp diode) Db 1 , a third diode (third clamp diode) Dc 1 , and a fourth diode (fourth clamp diode) Dd 1  in addition to the components of the first embodiment. The same is applied to the other battery state monitoring circuits. In the following description, the battery state monitoring circuit BMB 1  will be representatively described. 
     The first diode Da 1  has an anode terminal connected to the VSS 1 , and a cathode terminal connected to the drain terminal of the first output transistor C 1 . The first diode Da 1  has such a characteristic as to generate a reverse current when a reverse voltage corresponding to a voltage (for example, 4.5V) that exceeds the withstand voltage of the battery state monitoring circuit is applied between the anode terminal and the cathode terminal. The second diode Db 1  has an anode terminal connected to the VSS 1 , and a cathode terminal connected to the input terminal of the second inverter E 1 . It is assumed that the voltage drop of the second diode Db 1  is 0.7 V. 
     The third diode Dc 1  has an anode terminal connected to the VSS 1 , and a cathode terminal connected to the drain terminal of the second output transistor I 1 . The third diode Dc 1  has such a characteristic as to generate a reverse current when a reverse voltage corresponding to a voltage that exceeds the withstand voltage of the battery state monitoring circuit is applied between the anode terminal and the cathode terminal. The fourth diode Dd 1  has an anode terminal connected to the VSS 1 , and a cathode terminal connected to the input terminal of the fourth inverter K 1 . It is assumed that the voltage drop of the fourth diode Dd 1  is 0.7 V. 
     Also, resistive elements are connected between the first transmitting terminal of the downstream side battery state monitoring circuit and the first receiving terminal of the upstream side battery state monitoring circuit, and between the second transmitting terminal of the downstream side battery state monitoring circuit and the second receiving terminal of the upstream side battery state monitoring circuit, respectively. Specifically, a resistive element Ra 1  is connected between the first transmitting terminal PC 2  of the battery state monitoring circuit BMB 2  and the first receiving terminal PE 1  of the battery state monitoring circuit BMB 1 , and a resistive element Rb 1  is connected between the second transmitting terminal PD 2  of the battery state monitoring circuit BMB 2  and the second receiving terminal PF 1  of the battery state monitoring circuit BMB 1 , respectively. 
     Subsequently, a description will be given of the operation of the battery device according to the third embodiment, which is configured as described above. The operation in the cell balance state is identical with that in the first embodiment, and therefore its description will be omitted. 
     (Normal State) 
     First, a description will be given of a normal state, that is, a case in which all the voltages of the batteries BT 1  to BT n  are lower than the overcharge voltage, and equal to or higher than the overdischarge voltage. In the normal state thus defined, the overcharge detector circuit A 1  of the battery state monitoring circuit BMB 1  outputs the overcharge detection signal of low level to the first NOR circuit B 1 . 
     In this situation, the first output transistor C 2  of the battery state monitoring circuit BMB 2  is on. As a result, the input terminal of the second inverter E 1  of the battery state monitoring circuit BMB 1  becomes at low level, and the output signal of low level is output from the first inverter D 1  to the first NOR circuit B 1 . The first NOR circuit B 1  outputs the negative OR signal of high level to the gate terminal of the first output transistor C 1 . As a result, because the first output transistor C 1  is turned on, the first transmitting terminal PC 1  becomes at low level, and the first transistor  10  is turned on. 
     In this situation, when the first output transistor C 2  of the battery state monitoring circuit BMB 2  is on, the first receiving terminal PE 1  of the battery state monitoring circuit BMB 1  is connected to the VSS 2  through the resistive element Ra 1 . However, since the first receiving terminal PE 1  is equipped with the second diode Db 1 , the voltage is clamped to VSS 1 −0.7 V, and does not decrease lower than that value. 
     Also, in the above normal state, the overdischarge detector circuit G 1  of the battery state monitoring circuit BMB 1  outputs the overdischarge detection signal of low level to the second NOR circuit H 1 . In this situation, the second output transistor I 2  of the battery state monitoring circuit BMB 2  is also on. Therefore, the input terminal of the fourth inverter K 1  in the battery state monitoring circuit BMB 1  becomes at low level, and the output signal of low level is output to the second NOR circuit H 1  from the third inverter J 1 . The second NOR circuit H 1  outputs the negative OR signal of high level to the gate terminal of the second output transistor I 1 . As a result, because the second output transistor I 1  is turned on, the second transmitting terminal PD 1  becomes at low level, and the second transistor  11  is turned on. 
     Similarly, the voltage of the second receiving terminal PF 1  of the battery state monitoring circuit BMB 1  is clamped to VSS 1 −0.7 V. 
     As described above, in the normal state, because the first transistor  10  and the second transistor  11  are turned on, the battery device is chargeable and dischargeable. 
     (Overcharged State) 
     Subsequently, a description will be given of an overcharged state, that is, a case in which a charger is connected between the first external terminal  30  and the second external terminal  31  to charge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes equal to or higher than the overcharge voltage. In the following description, it is assumed that the voltage of the battery BT 2  is equal to or higher than the overcharge voltage. 
     In this case, the overcharge detector circuit A 2  of the battery state monitoring circuit BMB 2  outputs the overcharge detection signal of high level to the first NOR circuit B 2 . In this situation, because the output signal of low level is output from the first inverter D 2 , the first NOR circuit B 2  outputs the negative OR signal of low level to the gate terminal of the first output transistor C 2 . As a result, the first output transistor C 2  is turned off. 
     That is, the input terminal of the second inverter E 1  is pulled up to high level by means of the first current source F 1 . As a result, a voltage recognized as high level is applied to the input terminal of the second inverter E 1 , and the output signal of high level is output to the first NOR circuit B 1  from the first inverter D 1 . On the other hand, because the overcharge detector circuit A 1  outputs the overcharge detection signal of low level to the first NOR circuit B 1 , the first NOR circuit B 1  outputs the negative OR signal of low level to the gate terminal of the first output transistor C 1 . As a result, the first output transistor C 1  is turned off. 
     In this situation, the first transmitting terminal PC 2  of the battery state monitoring circuit BMB 2  is pulled up to VDD 1  through the resistive element Ra 1 . However, since the first transmitting terminal PC 2  is equipped with a first diode Da 2 , the terminal voltage is clamped to VSS 2 +4.5 V by a voltage (4.5 V) that causes the reverse current of the first diode Da 2  to be generated. Also, the resistance of the resistive element Ra 1  is set to a value that allows the voltage of the input terminal of the second inverter E 1  to be pulled up to high level by the first current source F 1 . 
     As described above, when the first output transistor C 1  is turned off, the gate terminal of the first transistor  10  becomes at high level by means of the first resistive element  20 , and the first transistor  10  is turned off. As a result, the charging from the charger is prohibited. 
     (Overdischarged State) 
     Subsequently, a description will be given of an overdischarged state, that is, a case in which a load is connected between the first external terminal  30  and the second external terminal  31  to discharge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes lower than the overdischarge voltage. In the following description, it is assumed that the voltage of the battery BT 2  is lower than the overdischarge voltage. 
     In this case, the overdischarge detector circuit G 2  of the battery state monitoring circuit BMB 2  outputs the overdischarge detection signal of high level to the second NOR circuit H 2 . In this situation, because the output signal of low level is output from the third inverter J 2 , the second NOR circuit H 2  outputs the negative OR signal of low level to the gate terminal of the second output transistor I 2 . As a result, the second output transistor I 2  is turned off. 
     That is, the input terminal of the fourth inverter K 1  is pulled up to high level by means of the second current source L 1 . As a result, a voltage is recognized as high level is applied to the input terminal of the fourth inverter K 1 , and the output signal of high level is output to the second NOR circuit H 1  from the third inverter J 1 . On the other hand, because the overdischarge detector circuit G 1  outputs the overdischarge detection signal of low level to the second NOR circuit H 1 , the second NOR circuit H 1  outputs the negative OR signal of low level to the gate terminal of the second output transistor I 1 . As a result, the second output transistor I 1  is turned off. 
     In this situation, the second transmitting terminal PD 2  of the battery state monitoring circuit BMB 2  is pulled up to VDD 1  through the resistive element Rb 1 . However, since the second transmitting terminal PD 2  is equipped with a third diode Dc 2 , the terminal voltage is clamped to VSS 2 +4.5 V by a voltage (4.5 V) that causes the reverse current of the third diode Dc 2  to be generated. Also, the resistance of the resistive element Rb 1  is set to a value that allows the voltage of the input terminal of the fourth inverter K 1  to be pulled up to high level by the second current source L 1 . 
     As described above, when the second output transistor I 1  is turned off, the gate terminal of the second transistor  11  becomes at high level, and the second transistor  11  is turned off. As a result, the discharging to the load is prohibited. 
     In the first embodiment, in the battery state monitoring circuit that has detected the overcharged state or the overdischarged state, the first output transistor or the second output transistor are turned off, and a voltage for two cells (two batteries) is applied to the downstream side first output transistor or second output transistor which has been turned off by the pull-up operation in the upstream side battery state monitoring circuit. That is, the withstand voltage of one battery state monitoring circuit needs to be equal to or higher than the voltage for at least two cells. In contrast, in the third embodiment, in the battery state monitoring circuit that has detected the overcharged state or the overdischarged state, the first output transistor or the second output transistor are turned off, and a voltage for one cell (one battery) is applied to the downstream side first output transistor or second output transistor which has been turned off by the pull-up operation in the upstream side battery state monitoring circuit. That is, the withstand voltage of one battery state monitoring circuit needs to be equal to or higher than the voltage for at least one cell. As a result, according to the third embodiment, the battery state monitoring circuit that is lower in withstand voltage than that of the first embodiment can be fabricated, and a range of the available manufacturing process is further broadened. As in the first embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. 
     Fourth Embodiment 
     Subsequently, a description will be given of a battery device according to a fourth embodiment.  FIG. 6  is a circuit configuration diagram showing the battery device according to the fourth embodiment. As shown in the figure, in the fourth embodiment, two types of diodes are disposed in the battery state monitoring circuit of the second embodiment. That is, when it is assumed that the symbols of the battery state monitoring circuits are BMC 1  to BMC n , the battery state monitoring circuit BMC n  is newly equipped with a first diode De n , a second diode Df n , a third diode Dg n , and a fourth diode Dh n  in addition to the components of the second embodiment. The same is applied to the other battery state monitoring circuits. In the following description, the battery state monitoring circuit BMC n  will be representatively described. 
     The first diode De n  has an anode terminal connected to the drain terminal of the first output transistor R n , and a cathode terminal connected to the VDD n . The first diode De n  has such a characteristic as to generate a reverse current when a reverse voltage corresponding to a voltage (for example, 4.5 V) that exceeds the withstand voltage of the battery state monitoring circuit is applied between the anode terminal and the cathode terminal. The second diode Df n  has an anode terminal connected to the input terminal of the second inverter S n , and a cathode terminal connected to the VDD n . It is assumed that the voltage drop of the second diode Df n  is 0.7 V. 
     The third diode Dg n  has an anode terminal connected to the drain terminal of the second output transistor V n , and a cathode terminal connected to the VDD n . The third diode Dg n  has such a characteristic as to generate a reverse current when a reverse voltage corresponding to a voltage (for example, 4.5 V) that exceeds the withstand voltage of the battery state monitoring circuit is applied between the anode terminal and the cathode terminal. The fourth diode Dh n  has an anode terminal connected to the input terminal of the fourth inverter W n , and a cathode terminal connected to the VDD n . It is assumed that the voltage drop of the fourth diode Dh n  is 0.7 V. 
     Also, resistive elements are connected between the first transmitting terminal of the upstream side battery state monitoring circuit and the first receiving terminal of the downstream side battery state monitoring circuit, and between the second transmitting terminal of the upstream side battery state monitoring circuit and the second receiving terminal of the downstream side battery state monitoring circuit, respectively. Specifically, a resistive element Ra n-1  is connected between the first transmitting terminal PC n-1  of the battery state monitoring circuit BMC n-1  and the first receiving terminal PE n  of the battery state monitoring circuit BMC n , and a resistive element Rb n-1  is connected between the second transmitting terminal PD n-1  of the battery state monitoring circuit BMC n-1  and the second receiving terminal PF n-1  of the battery state monitoring circuit BMC n , respectively. 
     Subsequently, a description will be given of the operation of the battery device according to the fourth embodiment, which is configured as described above. The operation in the cell balance state is identical with that in the first embodiment, and therefore its description will be omitted. 
     (Normal State) 
     First, a description will be given of a normal state, that is, a case in which all the voltages of the batteries BT 1  to BT n  are lower than the overcharge voltage, and equal to or higher than the overdischarge voltage. In the normal state thus defined, the overcharge detector circuit A n  of the battery state monitoring circuit BMC n  outputs the overcharge detection signal of low level to the first NOR circuit B n . 
     In this situation, the first output transistor R n-1  of the battery state monitoring circuit BMC n-1  is on. As a result, the input terminal of the second inverter S n  of the battery state monitoring circuit BMC n  becomes at high level, and the output signal of low level is output from the second inverter S n  to the first NOR circuit B n . The first NOR circuit B n  outputs the negative OR signal of high level to the first inverter Q n , and the first inverter Q n  outputs the logical inversion signal of low level to the gate terminal of the first output transistor R n . As a result, because the first output transistor R n  is turned on, the first transmitting terminal PC n  becomes at high level, and the first transistor  12  is turned on. 
     Also, in the above normal state, the overdischarge detector circuit G n  of the battery state monitoring circuit BMC n  outputs the overdischarge detection signal of low level to the second NOR circuit H n . In this situation, the second output transistor V n-1  of the battery state monitoring circuit BMC n-1  is on. Therefore, the input terminal of the fourth inverter W n  in the battery state monitoring circuit BMC n  becomes at high level, and the output signal of low level is output to the second NOR circuit H n  from the fourth inverter W n . The second NOR circuit H n  outputs the negative OR signal of high level to the third inverter U n , and the third inverter U n  outputs the logical inversion signal of low level to the gate terminal of the second output transistor V n . As a result, because the second output transistor V n  is turned on, the second transmitting terminal PD n  becomes at high level, and the second transistor  13  is turned on. 
     As described above, in the normal state, because the first transistor  12  and the second transistor  13  are turned on, the battery device is chargeable and dischargeable. 
     (Overcharged State) 
     Subsequently, a description will be given of an overcharged state, that is, a case in which a charger is connected between the first external terminal  30  and the second external terminal  31  to charge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes equal to or higher than the overcharge voltage. In the following description, it is assumed that the voltage of the battery BT n-1  is equal to or higher than the overcharge voltage. 
     In this case, the overcharge detector circuit A n-1  of the battery state monitoring circuit BMC n-1  outputs the overcharge detection signal of high level to the first NOR circuit B n-1 . In this situation, because the output signal of low level is output from the second inverter S n-1 , the first NOR circuit B n-1  outputs the negative OR signal of low level to the first inverter Q n-1 , and the first inverter Q n-1  outputs the logical inversion signal of high level to the gate terminal of the first output transistor R n-1 . As a result, the first output transistor R n-1  is turned off. 
     That is, the input terminal of the second inverter S n  is pulled down to low level by means of the first current source T n . When the pull-down voltage becomes equal to or lower than VDD n −4.5 V, a current flows in the VSS n  through a first diode De n-1  of the battery state monitoring circuit BMC n-1 . That is, the input terminal of the second inverter S n  is clamped to VDD n −4.5 V, and in that condition, the voltage does not satisfy the operating voltage (voltage that is recognized as low level) of the second inverter S n . Therefore, the resistance of the resistive element Ra n-1  is set so that the voltage of the input terminal of the second inverter S n  reaches the operating voltage. 
     With the above arrangement, a voltage recognized as low level is applied to the input terminal of the second inverter S n , and the output signal of high level is output to the first NOR circuit B n  from the second inverter S n . On the other hand, because the overcharge detector circuit A n  outputs the overcharge detection signal of low level to the first NOR circuit B n , the first NOR circuit B n  outputs the negative OR signal of low level to the first inverter Q n , and the first inverter Q n  outputs the logical inversion signal of high level to the gate terminal of the first output transistor R n . As a result, the first output transistor R n  is turned off. 
     As described above, when the first output transistor R n  is turned off, the gate terminal of the first transistor  12  becomes at low level, and the first transistor  12  is turned off. As a result, the charging from the charger is prohibited. 
     (Overdischarged State) 
     Subsequently, a description will be given of an overdischarged state, that is, a case in which a load is connected between the first external terminal  30  and the second external terminal  31  to discharge the batteries BT 1  to BT n , and at least one voltage of those batteries BT 1  to BT n  becomes lower than the overdischarge voltage. In the following description, it is assumed that the voltage of the battery BT n-1  is lower than the overdischarge voltage. 
     In this case, the overdischarge detector circuit G n-1  of the battery state monitoring circuit BMC n-1  outputs the overdischarge detection signal of high level to the second NOR circuit H n-1 . In this situation, because the output signal of low level is output from the fourth inverter W n-1 , the second NOR circuit H n-1  outputs the negative OR signal of low level to the third inverter U n-1 , and the third inverter U n-1  outputs the logical inversion signal of high level to the gate terminal of the second output transistor V n-1 . As a result, the second output transistor V n-1  is turned off. 
     That is, the input terminal of the fourth inverter W n  is pulled down to low level by means of the second current source X n . When the pull-down voltage becomes equal to or lower than VDD n −4.5 V, a current flows in the VSS n  through a third diode Dg n-1  of the battery state monitoring circuit BMC n-1 . That is, the input terminal of the fourth inverter W n  is clamped to VDD n −4.5 V, and in that condition, the voltage does not satisfy the operating voltage (voltage that is recognized as low level) of the fourth inverter W n . Therefore, the resistance of the resistive element Rb n-1  is set so that the voltage of the input terminal of the fourth inverter W n  reaches the operating voltage. 
     With the above arrangement, a voltage recognized as low level is applied to the input terminal of the fourth inverter W n , and the output signal of high level is output to the second NOR circuit H n  from the fourth inverter W n . On the other hand, because the overdischarge detector circuit G n  outputs the overdischarge detection signal of low level to the second NOR circuit H n , the second NOR circuit H n  outputs the negative OR signal of low level to the third inverter U n , and the third inverter U n  outputs the logical inversion signal of high level to the gate terminal of the second output transistor V n . As a result, the second output transistor V n  is turned off. 
     As described above, when the second output transistor V n  is turned off, the gate terminal of the second transistor  13  becomes at low level, and the second transistor  13  is turned off. As a result, the discharging to the load is prohibited. 
     As described above, according to the fourth embodiment, the withstand voltage of one battery state monitoring circuit needs to be equal to or higher than the voltage for at least one cell as in the third embodiment. As a result, according to the fourth embodiment, the battery state monitoring circuit that is further lower in withstand voltage than that of the second embodiment can be fabricated, and a range of the available manufacturing process is further broadened. As in the second embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. 
     Fifth Embodiment 
     Subsequently, a description will be given of a battery device according to a fifth embodiment.  FIG. 7  is a circuit configuration diagram showing the battery device according to the fifth embodiment. As shown in the figure, in the fifth embodiment, the resistive elements that are disposed in the exterior of the battery state monitoring circuit in the third embodiment are disposed in the interior of the battery state monitoring circuit. 
     A battery state monitoring circuit BMD 1  will be representatively described. The resistive element Ra 1  is connected between the first receiving terminal PE 1  and the cathode terminal of the second diode Db 1  in the battery state monitoring circuit BMD 1 . Also, the resistive element Rb 1  is connected between the second receiving terminal PF 1  and the cathode terminal of the fourth diode Dd 1 . 
     The operation is identical with that in the third embodiment, and therefore its description will be omitted. 
     With the above configuration, a manufacturer of the battery device may merely prepare the battery state monitoring circuits BMD 1  of the same number as the number of batteries, and connect the upstream side and downstream side battery state monitoring circuits through no resistive element, thereby contributing to a reduction in manufacturing process. The provision of the resistive elements in the interior of the battery state monitoring circuit causes an increase in sizes of the battery state monitoring circuit and an increase in costs. In order to prevent this drawback, there can be applied the third embodiment. 
     Sixth Embodiment 
     Subsequently, a description will be given of a battery device according to a sixth embodiment.  FIG. 8  is a circuit configuration diagram showing the battery device according to the sixth embodiment. As shown in the figure, in the sixth embodiment, the resistive elements that are disposed in the exterior of the battery state monitoring circuit in the fourth embodiment are disposed in the interior of the battery state monitoring circuit. 
     A battery state monitoring circuit BME n  will be representatively described. A resistive element Ra n  is connected between the anode terminal of the diode Do n  and the anode terminal of the first diode De n  in the battery state monitoring circuit BME n . Also, a resistive element Rb n  is connected between the anode terminal of the third diode Dg n  and the second transmitting terminal PD n . 
     The operation is identical with that in the fourth embodiment, and therefore its description will be omitted. 
     With the above configuration, a manufacturer of the battery device may merely prepare the battery state monitoring circuits BME n  of the same number as the number of batteries, and connect the upstream side and downstream side battery state monitoring circuits through no resistive element, thereby contributing to a reduction in manufacturing process. The provision of the resistive elements in the interior of the battery state monitoring circuit causes an increase in sizes of the battery state monitoring circuit and an increase in costs. In order to prevent this drawback, there can be applied the fourth embodiment. 
     Alternatively, the resistive element Ra n  may be connected between the input terminal of the second inverter S n  and the first receiving terminal PE n , and the resistive element Rb n  may be connected between the input terminal of the fourth inverter W n  and the second receiving terminal PF n . Also, the resistive element Ra n  may be connected between the anode terminal of the second diode Df n  and the first receiving terminal PE n , and the resistive element Rb n  may be connected between the cathode terminal of the fourth diode Dh n  and the second receiving terminal PF n . 
     Seventh Embodiment 
     Subsequently, a description will be given of a battery device according to a seventh embodiment.  FIG. 9  is a circuit configuration diagram showing the battery device according to the seventh embodiment. As shown in the figure, the seventh embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BM 1  to BM n  of the first embodiment. In order to distinguish from the first embodiment, the symbols of the battery state monitoring circuits in the seventh embodiment are denoted by BM 1 ′ to BM n ′. In the seventh embodiment, a discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BM 1 ′ to BM n ′. Specifically, an anode terminal of the diode Do is connected to the gate terminal of the first transistor  10 , and a cathode terminal of the diode Do is connected to the first transmitting terminal PC 1  of the battery state monitoring circuit BM 1 . 
     With the battery device configured as described above, as in the first embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit. 
     Eighth Embodiment 
     Subsequently, a description will be given of a battery device according to an eighth embodiment.  FIG. 10  is a circuit configuration diagram showing the battery device according to the eighth embodiment. As shown in the figure, the eighth embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BMA 1  to BMA n  of the second embodiment. In order to distinguish from the second embodiment, the symbols of the battery state monitoring circuits in the eighth embodiment are denoted by BMA 1 ′ to BMA n ′. In the eighth embodiment, the discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BMA 1 ′ to BMA n ′. Specifically, the cathode terminal of the diode Do is connected to the gate terminal of the first transistor  12 , and the anode terminal of the diode Do is connected to the first transmitting terminal PC n  of the battery state monitoring circuit BMA n . 
     With the battery device configured as described above, as in the second embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit. 
     Ninth Embodiment 
     Subsequently, a description will be given of a battery device according to a ninth embodiment.  FIG. 11  is a circuit configuration diagram showing the battery device according to the ninth embodiment. As shown in the figure, the ninth embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BMB 1  to BMB n  of the third embodiment. In order to distinguish from the third embodiment, the symbols of the battery state monitoring circuits in the ninth embodiment are denoted by BMB 1 ′ to BMB n ′. In the ninth embodiment, the discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BMB 1 ′ to BMB n ′. Specifically, the anode terminal of the diode Do is connected to the gate terminal of the first transistor  10 , and the cathode terminal of the diode Do is connected to the first transmitting terminal PC 1  of the battery state monitoring circuit BMB 1 . 
     With the battery device configured as described above, as in the third embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit. 
     Tenth Embodiment 
     Subsequently, a description will be given of a battery device according to a tenth embodiment.  FIG. 12  is a circuit configuration diagram showing the battery device according to the tenth embodiment. As shown in the figure, the tenth embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BMC 1  to BMC n  of the fourth embodiment. In order to distinguish from the fourth embodiment, the symbols of the battery state monitoring circuits in the tenth embodiment are denoted by BMC 1 ′ to BMC n ′. In the tenth embodiment, the discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BMC 1 ′ to BMC n ′. Specifically, the cathode terminal of the diode Do is connected to the gate terminal of the first transistor  12 , and the anode terminal of the diode Do is connected to the first transmitting terminal PC n  of the battery state monitoring circuit BMC n . 
     With the battery device configured as described above, as in the fourth embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit. 
     Eleventh Embodiment 
     Subsequently, a description will be given of a battery device according to an eleventh embodiment.  FIG. 13  is a circuit configuration diagram showing the battery device according to the eleventh embodiment. As shown in the figure, the eleventh embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BMD 1  to BMD n  of the fifth embodiment. In order to distinguish from the fifth embodiment, the symbols of the battery state monitoring circuits in the eleventh embodiment are denoted by BMD 1 ′ to BMD n ′. In the eleventh embodiment, the discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BMD 1 ′ to BMD n ′. Specifically, the anode terminal of the diode Do is connected to the gate terminal of the first transistor  10 , and the cathode terminal of the diode Do is connected to the first transmitting terminal PC 1  of the battery state monitoring circuit BMD 1 . 
     With the battery device configured as described above, as in the fifth embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit. 
     Twelfth Embodiment 
     Subsequently, a description will be given of a battery device according to a twelfth embodiment.  FIG. 14  is a circuit configuration diagram showing the battery device according to the twelfth embodiment. As shown in the figure, the twelfth embodiment is directed to the battery device in which the discharge leak current prevention diodes Do 1  to Do n  are not disposed in the respective battery state monitoring circuits BME 1  to BME n  of the sixth embodiment. In order to distinguish from the sixth embodiment, the symbols of the battery state monitoring circuits in the twelfth embodiment are denoted by BME 1 ′ to BME n ′. In the twelfth embodiment, the discharge leak current prevention diode Do is disposed in the exterior of the battery state monitoring circuits BME 1 ′ to BAE n ′. Specifically, the cathode terminal of the diode Do is connected to the gate terminal of the first transistor  12 , and the anode terminal of the diode Do is connected to the first transmitting terminal PC n  of the battery state monitoring circuit BME n . 
     With the battery device configured as described above, as in the sixth embodiment, the occurrence of the discharge leak current can be prevented, and the disruption of the voltage balance between the batteries as in the conventional technology does not occur. As a result, it is possible to eliminate the load on the user such as the costs and time required for battery exchange. Also, because it is unnecessary to provide the discharge leak current prevention diode within the battery state monitoring circuit, it is possible to reduce the costs and downsize the circuit.