Abstract:
Provided is a battery state monitoring circuit including: a charge/discharge control circuit for detecting and controlling a state of a secondary battery; an automatic recovery circuit; a temperature sensor circuit; and a comparator for comparing a voltage of an output terminal of the automatic recovery circuit and a voltage of the secondary battery, and outputting a signal indicative of a result of the comparison to the temperature sensor circuit, to control an operation of the temperature sensor circuit. The temperature sensor circuit operates only when the output of the automatic recovery circuit is larger, that is, only when a charger is connected between external terminals.

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-065138 filed on Mar. 19, 2010, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery state monitoring circuit for detecting a voltage and an abnormality of a secondary battery and a battery device including the battery state monitoring circuit, and more particularly, to a battery state monitoring circuit incorporating a temperature sensor in a charge/discharge control circuit and a battery device including the battery state monitoring circuit. 
     2. Description of the Related Art 
       FIG. 3  illustrates a circuit diagram of a conventional battery device incorporating a temperature sensor. The conventional battery device incorporating the temperature sensor includes a secondary battery  101 , a battery state monitoring circuit  309 , an external terminal  106 , and an external terminal  107 . The battery state monitoring circuit  309  includes an overcharge detection circuit  301 , an overdischarge detection circuit  305 , a control circuit  302 , an overheat detection circuit  304 , a temperature sensor  307 , an overcurrent detection circuit  303 , a discharge field-effect transistor (FET)  306 , a charge FET  308 . 
     Connection is made as follows. The positive terminal side of the secondary battery  101  is connected to the overcharge detection circuit  301 , the overdischarge detection circuit  305 , and the external terminal  106 , and the negative terminal side thereof is connected to a source of the discharge FET  306 . The control circuit  302  is connected to an output of the overcharge detection circuit  301 , an output of the overdischarge detection circuit  305 , an output of the overcurrent detection circuit  303 , and an output of the overheat detection circuit  304 . The discharge FET  306  has a gate connected to an output of the control circuit  302  and a drain connected to a drain of the charge FET  308 . The charge FET  308  has a gate connected to another output of the control circuit  302  and a source connected to an input of the overcurrent detection circuit  303  and the external terminal  107 . 
     When the charge FET  308  enters an abnormal overheated state due to overcurrent during charge, the overheat detection circuit  304  notifies the control circuit  302  of the abnormal state so that the control circuit  302  operates to change the gate of the charge FET  308  to L to disconnect a charge current. Therefore, the charge FET  308  for charge control can be protected from abnormal overheat (see, for example, Japanese Patent Application Laid-open No. 2007-124775). 
     The battery device needs overheat protection by a temperature sensor circuit even when the secondary battery is charged from 0 V. The temperature sensor circuit obtains power from between the external terminals because, otherwise if the power is obtained from the secondary battery side, the temperature sensor circuit does not operate when the battery voltage is 0 V, and hence the overheat protection does not work. In the conventional technology, however, current consumption of the temperature sensor circuit is a load to an automatic recovery circuit, and hence there is a problem that the automatic recovery circuit cannot operate normally at the time of recovery from an overcurrent protection state using an automatic recovery function. This is because the automatic recovery circuit outputs a minute current so as to suppress consumption of the battery and the output current of the automatic recovery circuit is completely consumed by the overheat detection circuit to hinder the automatic recovery operation. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the problem described above, and provides a battery state monitoring circuit in which an automatic recovery function normally works, thereby being capable of lowering power consumption, and also provides a battery device including the battery state monitoring circuit. 
     In order to solve the conventional problem, a battery device including a battery state monitoring circuit according to the present invention has the following configuration. 
     The battery state monitoring circuit includes: a charge/discharge control circuit for detecting and controlling a state of a secondary battery; an automatic recovery circuit; a temperature sensor circuit; and a comparator for comparing a voltage of an output terminal of the automatic recovery circuit, that is, an overcurrent detection terminal and a voltage of the secondary battery, and controlling an operation of the temperature sensor circuit by an output signal indicative of a result of the comparison. 
     According to the battery device of the present invention, it is possible to suspend the operation of the temperature sensor circuit until the voltage of the overcurrent detection terminal becomes higher than a voltage of a positive terminal of the secondary battery, that is, until the connection of a charger is established. As a result, the function of automatic recovery from an overcurrent protection state can normally work. The comparator obtains power from the output of the automatic recovery circuit, that is, from the overcurrent detection terminal. However, the current consumption of the comparator is tiny enough not to hinder the operation of the automatic recovery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a circuit diagram of a battery device including a battery state monitoring circuit according to a first embodiment of the present invention; 
         FIG. 2  is a circuit diagram of a battery device including a battery state monitoring circuit according to a second embodiment of the present invention; and 
         FIG. 3  is a circuit diagram of a conventional battery device including a battery state monitoring circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, modes for embodying the present invention are described. 
     First Embodiment 
       FIG. 1  is a circuit diagram of a battery device including a battery state monitoring circuit according to a first embodiment of the present invention. 
     The battery device according to the first embodiment includes a secondary battery  101 , a battery state monitoring circuit  109 , a discharge control P-channel field-effect transistor (FET)  102 , a charge control P-channel FET  103 , external terminals  106  and  107  to which a load  104  or a charger  105  is to be connected, a resistor  108 . The battery state monitoring circuit  109  includes an automatic recovery circuit  111 , a comparator  112 , a temperature sensor circuit  113 , a charge/discharge control circuit  114 , a 0 V charge control circuit  115 , an NMOS transistor  116 , and a diode  117 . 
     The automatic recovery circuit  111  and the charge/discharge control circuit  114  use the secondary battery  101  as power supply. The comparator  112 , the temperature sensor circuit  113 , and the 0 V charge control circuit  115  are each connected to an overcurrent detection terminal  123  for positive power supply and connected to a negative terminal of the secondary battery  101  for negative power supply. 
     The automatic recovery circuit  111  has an output connected to the overcurrent detection terminal  123 . The comparator  112  has a non-inverting input terminal connected to the overcurrent detection terminal  123 , an inverting input terminal connected to a positive terminal of the secondary battery  101 , and an output connected to the temperature sensor circuit  113 . The temperature sensor circuit  113  has an output connected to the charge/discharge control circuit  114 . The charge/discharge control circuit  114  has an input connected to the overcurrent detection terminal  123 , one output connected to a discharge control output terminal  121 , and another output connected to a gate of the NMOS transistor  116 . The NMOS transistor  116  has a source connected to the negative terminal of the secondary battery  101  and a drain connected to a cathode of the diode  117 . The diode  117  has an anode connected to a charge control output terminal  122 . The 0 V charge control circuit  115  has an input connected to the overcurrent detection terminal  123 , and is included in the charge/discharge control circuit  114 . The discharge control P-channel FET  102  has a gate connected to the discharge control output terminal  121 , a source connected to the positive terminal of the secondary battery  101 , and a drain connected to a drain of the charge control P-channel FET  103 . The charge control P-channel FET  103  has a gate connected to the charge control output terminal  122  and a source connected to the external terminal  106 . The resistor  108  has one end connected to the charge control output terminal  122  and another end connected to the external terminal  106 . The overcurrent detection terminal  123  is connected to the external terminal  106 , and the external terminal  107  is connected to the negative terminal of the secondary battery  101 . 
     The comparator  112  has a slight positive offset at the non-inverting input terminal, and outputs a signal of H when a voltage of the overcurrent detection terminal  123  becomes higher than a voltage of the positive terminal of the secondary battery  101  by the offset voltage. The temperature sensor circuit  113  suspends its operation in response to a signal of L received from the comparator  112 , and starts the operation in response to the signal of H. 
     Next, an operation of the battery device according to the first embodiment is described. 
     When a heavy load is connected between the external terminals  106  and  107 , the charge/discharge control circuit  114  detects overcurrent and enables an overcurrent protection function to turn OFF the discharge control P-channel FET  102 . The voltage of the overcurrent detection terminal  123  is reduced to around 0 V. The automatic recovery circuit  111  operates in preparation for automatic recovery when the heavy load is removed, and supplies a current to the overcurrent detection terminal  123 . After that, when the heavy load is removed, the voltage of the overcurrent detection terminal  123  increases gradually. At this time, because the comparator  112  has the slight positive offset at the non-inverting input terminal, the comparator  112  outputs the signal of L to suspend the circuit operation of the temperature sensor circuit  113 . Then, the charge/discharge control circuit  114  detects that the heavy load has been removed, and turns ON the discharge control P-channel FET  102 . This way, the voltage of the overcurrent detection terminal  123  becomes equal to the voltage of the positive terminal of the secondary battery  101 . 
     The positive offset voltage at the non-inverting input terminal of the comparator  112  is set to a voltage lower than a value determined by multiplying the sum of an ON-state resistance of the discharge control P-channel FET  102  and an ON-state resistance of the charge control P-channel FET  103  by a charge current of the charger  105 . The comparator  112  obtains power from the output of the automatic recovery circuit  111 , that is, from the external terminal  106 , but does not hinder the operation of automatic recovery because the comparator  112  is designed to have tiny current consumption. 
     After that, when the charger  105  is connected between the external terminals  106  and  107 , the voltage of the overcurrent detection terminal  123  is increased to be higher than the voltage of the positive terminal of the secondary battery  101 . Then, the comparator  112  outputs the signal of H so that the temperature sensor circuit  113  operates. This way, the temperature sensor circuit  113  operates only after the voltage of the overcurrent detection terminal  123  becomes higher than the voltage of the positive terminal of the secondary battery  101 . Therefore, the automatic recovery function can work successfully. 
     The temperature sensor circuit  113  operates only when the voltage of the overcurrent detection terminal  123  is higher than the voltage of the positive terminal of the secondary battery  101 . In other words, the temperature sensor circuit  113  operates only when the charger  105  is connected between the external terminals  106  and  107 . Therefore, in a normal state in which the charger  105  is not connected, the temperature sensor circuit  113  does not operate, to thereby lower current consumption. 
     Next, an operation of overheat protection at the time of charge when the secondary battery  101  has been discharged to around 0 V is described. When the charger  105  is connected, the 0 V charge control circuit  115  operates to change a gate voltage of the NMOS transistor  116  to H via the output of the charge/discharge control circuit  114  to turn ON the NMOS transistor  116 . Then, a current flows to the negative terminal of the secondary battery  101  from the external terminal  106  via the resistor  108 , the charge control output terminal  122 , the diode  117 , and the NMOS transistor  116 . This current causes voltage drop across the resistor  108  to increase a source-gate voltage of the charge control P-channel FET  103 . Accordingly, the charge control P-channel FET  103  is turned ON. The requirement for turning ON the charge control P-channel FET  103  is to apply a voltage of VTH or higher as the gate-source voltage. Because the secondary battery  101  is 0 V, when the charge control P-channel FET  103  is electrically connected, a source voltage thereof is decreased but the gate-source voltage stops at the voltage of VTH or higher. The voltage between the external terminals  106  and  107  at this time is a voltage substantially equal to the sum of a Vf voltage of the diode  117  and the voltage VTH of the charge control P-channel FET  103 . This voltage is higher than the positive terminal voltage of the secondary battery  101 , and hence the comparator  112  outputs H, which is high enough for the temperature sensor circuit  113  to operate. Therefore, the temperature sensor circuit  113  starts the circuit operation to enable the overheat protection function. 
     Second Embodiment 
       FIG. 2  is a circuit diagram of a battery device including a battery state monitoring circuit according to a second embodiment of the present invention.  FIG. 2  is different from  FIG. 1  in that the discharge control P-channel FET  102 , the charge control P-channel FET  103 , the NMOS transistor  116 , and the diode  117  are changed to a discharge control N-channel FET  201 , a charge control N-channel FET  202 , a PMOS transistor  211 , and a diode  212 , respectively. 
     Connection is made as follows. The automatic recovery circuit  111  and the charge/discharge control circuit  114  use the secondary battery  101  as power supply. The comparator  112 , the temperature sensor circuit  113 , and the 0 V charge control circuit  115  are each connected to the overcurrent detection terminal  123  for negative power supply and connected to the positive terminal of the secondary battery  101  for positive power supply. 
     The PMOS transistor  211  has a gate connected to the output of the charge/discharge control circuit  114 , a source connected to the positive terminal of the secondary battery  101 , and a drain connected to an anode of the diode  212 . The diode  212  has a cathode connected to the charge control output terminal  122 . The discharge control N-channel FET  201  has a gate connected to the discharge control output terminal  121 , a source connected to the negative terminal of the secondary battery  101 , and a drain connected to a drain of the charge control N-channel FET  202 . The charge control N-channel FET  202  has a gate connected to the charge control output terminal  122  and a source connected to the external terminal  107 . The resistor  108  has one end connected to the charge control output terminal  122  and another end connected to the external terminal  107 . The overcurrent detection terminal  123  is connected to the external terminal  107 , and the external terminal  106  is connected to the positive terminal of the secondary battery  101 . 
     Next, an operation is described. When a heavy load is connected between the external terminals  106  and  107 , the charge/discharge control circuit  114  detects overcurrent and enables the overcurrent protection function to turn OFF the discharge control N-channel FET  201 . Then, the voltage of the overcurrent detection terminal  123  becomes substantially equal to the voltage of the external terminal  106 . The automatic recovery circuit  111  operates in preparation for automatic recovery when the heavy load is removed, and supplies a current to the negative terminal of the secondary battery  101  from the overcurrent detection terminal  123 . After that, when the heavy load is removed, the voltage of the overcurrent detection terminal  123  decreases gradually. At this time, because the comparator  112  has the slight positive offset at the non-inverting input terminal, the comparator  112  outputs the signal of L to suspend the circuit operation of the temperature sensor circuit  113 . Then, the charge/discharge control circuit  114  detects that the heavy load has been removed, and turns ON the discharge control N-channel FET  201 . This way, the voltage of the overcurrent detection terminal  123  becomes equal to the voltage of the negative terminal of the secondary battery  101 . 
     The positive offset voltage at the non-inverting input terminal of the comparator  112  is set to a voltage lower than a value determined by multiplying the sum of an ON-state resistance of the discharge control N-channel FET  201  and an ON-state resistance of the charge control N-channel FET  202  by a charge current of the charger  105 . The comparator  112  obtains power from the output of the automatic recovery circuit  111 , that is, from the external terminal  106 , but does not hinder the operation of automatic recovery because the comparator  112  is designed to have tiny current consumption. 
     After that, when the charger  105  is connected between the external terminals  106  and  107 , the voltage of the overcurrent detection terminal  123  is decreased to be lower than the voltage of the negative terminal of the secondary battery  101 . Then, the comparator  112  outputs the signal of H so that the temperature sensor circuit  113  operates. This way, the temperature sensor circuit  113  operates only after the voltage of the overcurrent detection terminal  123  becomes lower than the voltage of the negative terminal of the secondary battery  101 . Therefore, the automatic recovery function can work successfully. 
     The temperature sensor circuit  113  operates only when the voltage of the overcurrent detection terminal  123  is lower than the voltage of the negative terminal of the secondary battery  101 . In other words, the temperature sensor circuit  113  operates only when the charger  105  is connected between the external terminals  106  and  107 . Therefore, in a normal state in which the charger  105  is not connected, the temperature sensor circuit  113  does not operate, to thereby lower current consumption. 
     Next, an operation of overheat protection at the time of charge when the secondary battery  101  has been discharged to around 0 V is described. When the charger  105  is connected, the 0 V charge control circuit  115  operates to change a gate voltage of the PMOS transistor  211  to L via the output of the charge/discharge control circuit  114  to turn ON the PMOS transistor  211 . Then, a current flows to the external terminal  107  from the positive terminal of the secondary battery  101  via the PMOS transistor  211 , the diode  212 , the charge control output terminal  122 , and the resistor  108 . This current causes voltage drop across the resistor  108  to increase a source-gate voltage of the charge control N-channel FET  202 . Accordingly, the charge control N-channel FET  202  is turned ON. The requirement for turning ON the charge control N-channel FET  202  is to apply a voltage of VTH or higher as the gate-source voltage. Because the secondary battery  101  is 0 V, when the charge control N-channel FET  202  is electrically connected, a source voltage thereof is increased but the gate-source voltage stops at the voltage of VTH or higher. The voltage between the external terminals  106  and  107  at this time is a voltage substantially equal to the sum of a Vf voltage of the diode  212  and the voltage VTH of the charge control N-channel FET  202 . This voltage is lower than the negative terminal voltage of the secondary battery  101 , and hence the comparator  112  outputs H, which is high enough for the temperature sensor circuit  113  to operate. Therefore, the temperature sensor circuit  113  starts the circuit operation to enable the overheat protection function.