Abstract:
Provided is a highly safe battery device in which the accuracy of an overcurrent detection current value and a short-circuit current value is improved and current consumption is reduced. A short-circuit and overcurrent detecting circuit includes: a reference voltage circuit configured to output a reference voltage generated when a constant current flows through an impedance element and a transistor having a resistance value that is changed depending on a voltage of a secondary battery; a first comparator circuit configured to compare a voltage of an overcurrent detecting terminal with the reference voltage; and a second comparator circuit configured to compare a voltage based on the voltage of the overcurrent detecting terminal with the reference voltage.

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2014-100196 filed on May 14, 2014, the entire contents of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery device including a secondary battery and a charge and discharge control circuit configured to detect a voltage and abnormality of the secondary battery to control charge and discharge of the secondary battery, and more particularly, to a charge and discharge control circuit and a battery device that are capable of preventing a battery from entering an abnormal state or preventing an excessive current from flowing through a battery or an apparatus connected to the battery. 
     2. Description of the Related Art 
       FIG. 4  is a circuit diagram illustrating a related-art battery device including a charge and discharge control circuit. The related-art battery device including the charge and discharge control circuit includes a secondary battery  11 , an N-channel discharge control field effect transistor  12 , an N-channel charge control field effect transistor  13 , a charge and discharge control circuit  14 , resistors  22  and  31 , a capacitor  32 , and external terminals  20  and  21 . The charge and discharge control circuit  14  includes a control circuit  15 , an overcurrent detecting circuit  530 , a short-circuit detecting circuit  540 , an overcurrent detecting terminal  19 , a charge control signal output terminal  41 , a discharge control signal output terminal  42 , a DS terminal  45 , a positive electrode power supply terminal  44 , and a negative electrode power supply terminal  43 . The overcurrent detecting circuit  530  includes a comparator circuit  101  and a reference voltage circuit  531 . The short-circuit detecting circuit  540  includes a comparator circuit  102  and a reference voltage circuit  541 . 
     The control circuit  15  includes resistors  504 ,  505 ,  506 ,  507 ,  518 , and  528 , reference voltage circuits  509  and  515 , comparator circuits  501 ,  508 , and  513 , an oscillator circuit  502 , a counter circuit  503 , a logic circuit  510 , a level shift circuit  511 , a delay circuit  512 , a logic circuit  520 , and NMOS transistors  517  and  519 . 
     Next, an operation of the related-art battery device including the charge and discharge control circuit is described. When a load is connected between the external terminals  20  and  21  and a current flows, a potential difference is generated between a negative electrode of the secondary battery  11  and the external terminal  21 . This potential difference is determined based on a current amount I 1  flowing between the external terminals  20  and  21 , a resistance value R 12  of the N-channel discharge control field effect transistor  12 , and a resistance value R 13  of the N-channel charge control field effect transistor  13 , and is represented by I 1 ×(R 12 +R 13 ). A voltage of the overcurrent detecting terminal  19  is equal to a voltage of the external terminal  21 . The comparator circuit  101  compares a voltage of the reference voltage circuit  531  with the voltage of the overcurrent detecting terminal  19 . When the voltage of the overcurrent detecting terminal  19  is higher, the N-channel discharge control field effect transistor  12  is turned off for overcurrent protection. A setting value of an overcurrent detection current value is represented by I DOP , a voltage of the reference voltage circuit  531  is represented by V 531 , a resistance value of the N-channel discharge control field effect transistor  12  is represented by R 12 , and a resistance value of the N-channel charge control field effect transistor  13  is represented by R 13 . A voltage of the external terminal  21  as a threshold voltage for the comparator circuit  101  to output a detection signal is V 531 . At this time, the current flowing between the external terminals  20  and  21  is obtained by dividing the voltage of the external terminal  21  by the sum of the resistance values of the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13 , and is represented by I DOP =V 531 /(R 12 +R 13 ). 
     A voltage of the overcurrent detecting terminal of the charge and discharge control circuit as a threshold voltage for the comparator circuit  101  to output a detection signal is referred to as “overcurrent detection voltage”. A voltage of the overcurrent detecting terminal of the charge and discharge control circuit as a threshold voltage for the comparator circuit  102  to output a detection signal is referred to as “short-circuit detection voltage”. 
     However, in the related art, the overcurrent detection voltage and the short-circuit detection voltage of the charge and discharge control circuit have constant values even when the secondary battery voltage or temperature changes, but the resistance value of the N-channel charge and discharge control field effect transistor changes along with a change in the secondary battery voltage or temperature, resulting in fluctuations in an overcurrent detection current value and a short-circuit detection current value. Accordingly, there is a problem in that the overcurrent detection current value and the short-circuit detection current value are low in accuracy to reduce the safety of the battery device. Further, there is another problem in that current consumption is high because two reference voltage circuits are used for the overcurrent detecting circuit and the short-circuit detecting circuit. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-mentioned problems, and aims at changing an overcurrent detection voltage and a short-circuit detection voltage of a charge and discharge control circuit so as to follow a change in a resistance value of an N-channel charge and discharge control field effect transistor caused by a change in a secondary battery voltage or temperature, to thereby prevent an overcurrent detection current value from being fluctuated by the change in the secondary battery voltage or temperature. Accordingly, the present invention provides a highly safe battery device in which the accuracy of the overcurrent detection current value and a short-circuit detection current value is improved with low current consumption. 
     In order to solve the related-art problems, a charge and discharge control circuit according to one embodiment of the present invention has the following configuration. 
     A short-circuit and overcurrent detecting circuit includes: a reference voltage circuit configured to output a reference voltage generated when a constant current flows through an impedance element and a transistor having a resistance value that is changed depending on a voltage of a secondary battery; a first comparator circuit configured to compare a voltage of an overcurrent detecting terminal with the reference voltage; and a second comparator circuit configured to compare a voltage based on the voltage of the overcurrent detecting terminal with the reference voltage. 
     According to the one embodiment of the present invention, a secondary battery voltage dependence and a temperature dependence of an overcurrent detection voltage and a short-circuit detection voltage of the charge and discharge control circuit may be matched with a secondary battery voltage dependence and a temperature dependence of a resistance value of a charge and discharge control switch, and hence even when the secondary battery voltage or temperature changes, an overcurrent detection current value and a short-circuit detection current value of the battery device are constant. Consequently, a highly safe battery device in which the accuracy of the overcurrent detection current value and the short-circuit detection current value is improved and current consumption is reduced may be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a charge and discharge control circuit and a battery device according to a first embodiment of the present invention. 
         FIG. 2  is a circuit diagram of a charge and discharge control circuit and a battery device according to a second embodiment of the present invention. 
         FIG. 3  is a circuit diagram of a charge and discharge control circuit and a battery device according to a third embodiment of the present invention. 
         FIG. 4  is a circuit diagram of a charge and discharge control circuit and a battery device according to the related art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a circuit diagram of a charge and discharge control circuit and a battery device according to a first embodiment of the present invention. 
     The charge and discharge control circuit and the battery device of the first embodiment include a secondary battery  11 , an N-channel discharge control field effect transistor  12 , an N-channel charge control field effect transistor  13 , a charge and discharge control circuit  14 , resistors  22  and  31 , a capacitor  32 , and external terminals  20  and  21 . The charge and discharge control circuit  14  includes a control circuit  15 , a short-circuit and overcurrent detecting circuit  110 , an overcurrent detecting terminal  19 , a charge control signal output terminal  41 , a discharge control signal output terminal  42 , a positive electrode power supply terminal  44 , and a negative electrode power supply terminal  43 . The short-circuit and overcurrent detecting circuit  110  includes comparator circuits  101  and  102 , a constant current circuit  103 , resistors  104 ,  106 , and  107 , and an NMOS transistor  105 . The constant current circuit  103 , the resistor  104 , and the NMOS transistor  105  form a reference voltage circuit. 
     The secondary battery  11  has a positive electrode connected to the external terminal  20  and the resistor  31 , and a negative electrode connected to the capacitor  32 , the negative electrode power supply terminal  43 , and a source and a back gate of the N-channel discharge control field effect transistor  12 . The positive electrode power supply terminal  44  is connected to a node of the resistor  31  and the capacitor  32 . The N-channel discharge control field effect transistor  12  has a gate connected to the discharge control signal output terminal  42 , and a drain connected to a drain of the N-channel charge control field effect transistor  13 . The N-channel charge control field effect transistor  13  has a gate connected to the charge control signal output terminal  41 , and a source and a back gate connected to the external terminal  21  and one terminal of the resistor  22 . The other terminal of the resistor  22  is connected to the overcurrent detecting terminal  19 . 
     The comparator circuit  101  has an inverting input terminal connected to the overcurrent detecting terminal  19 , a non-inverting input terminal connected to a node of one terminal of the constant current circuit  103  and one terminal of the resistor  104 , and an output terminal connected to the control circuit  15 . The NMOS transistor  105  has a gate connected to the positive electrode power supply terminal  44 , a drain connected to the other terminal of the resistor  104 , and a source connected to the negative electrode power supply terminal  43 . The other terminal of the constant current circuit  103  is connected to the positive electrode power supply terminal  44 . The comparator circuit  102  has an inverting input terminal connected to a node of one terminal of the resistor  106  and one terminal of the resistor  107 , a non-inverting input terminal connected to the node of the one terminal of the constant current circuit  103  and the one terminal of the resistor  104 , and an output terminal connected to the control circuit  15 . The other terminal of the resistor  106  is connected to the negative electrode power supply terminal  43 , and the other terminal of the resistor  107  is connected to the overcurrent detecting terminal  19 . The control circuit  15  has a power supply terminal connected to the positive electrode power supply terminal  44 , a ground terminal connected to the negative electrode power supply terminal  43 , a first output terminal connected to the discharge control signal output terminal  42 , and a second output terminal connected to the charge control signal output terminal  41 . 
     Next, operations of the charge and discharge control circuit and the battery device of this embodiment are described. When the voltage of the secondary battery  11  is equal to or lower than an overcharge detection voltage and equal to or higher than an overdischarge detection voltage, the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13  are controlled to be turned on. When a load is connected between the external terminals  20  and  21  in this state and a discharge current is caused to flow, a potential difference is generated between the negative electrode of the secondary battery  11  and the external terminal  21 . This potential difference is determined based on a current amount I 1  flowing between the external terminals  20  and  21 , a resistance value R 12  of the N-channel discharge control field effect transistor  12 , and a resistance value R 13  of the N-channel charge control field effect transistor  13 , and is represented by I 1 ×(R 12 +R 13 ). 
     The constant current circuit  103  causes a current to flow through the resistor  104  and the NMOS transistor  105  to generate a voltage, and outputs the voltage as a reference voltage of the reference voltage circuit. The comparator circuit  101  compares the reference voltage of the reference voltage circuit with a voltage of the overcurrent detecting terminal  19 . When the voltage of the overcurrent detecting terminal  19  is higher, the comparator circuit  102  outputs a detection signal to the control circuit  15  to turn off the N-channel discharge control field effect transistor  12  for overcurrent protection. 
     A setting value of an overcurrent detection current value is represented by I DOP , the reference voltage of the reference voltage circuit is represented by V ref , a resistance value of the N-channel discharge control field effect transistor  12  is represented by R 12 , and a resistance value of the N-channel charge control field effect transistor  13  is represented by R 13 . A voltage of the external terminal  21  as a threshold voltage for the comparator circuit  101  to output a detection signal is V ref . At this time, the current flowing between the external terminals  20  and  21  is obtained by dividing the voltage of the external terminal  21  by the sum of the resistance values of the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13 , and is represented by I DOP =V ref /(R 12 +R 13 ). 
     In this case, the resistance value of the N-channel field effect transistors has a gate-source voltage dependence and a temperature dependence. A source potential of the N-channel charge and discharge control field effect transistors is a negative electrode potential of the secondary battery, and a gate potential thereof is a positive electrode potential of the secondary battery. Accordingly, the resistance value (R 12 +R 13 ) of the N-channel charge and discharge control field effect transistors has a secondary battery voltage dependence and a temperature dependence. 
     The source of the NMOS transistor  105  is connected to the negative electrode power supply terminal  43  and the gate thereof is connected to the positive electrode power supply terminal  44 , and hence the NMOS transistor  105  creates the state in which a gate-source voltage thereof is the same as that of the N-channel charge and discharge control field effect transistors. When a length W and a length L of the NMOS transistor  105  are changed and an amount of current flowing into the NMOS transistor  105  is changed by the constant current circuit  103 , the secondary battery voltage dependence can be adjusted. Further, in order to adjust the overcurrent detection current value I DOP , which is represented by V ref /(R 12 +R 13 ), the absolute value of V ref  needs to be adjusted. Through optimization of the value of the resistor  104  based on the current value of the constant current circuit  103 , the adjustment can be performed. Further, when the absolute value of V ref  is calibrated, temperature characteristics of the resistor  104  need to be optimized so that temperature characteristics of V ref  match with temperature characteristics of the N-channel charge and discharge control field effect transistors. The temperature characteristics of the resistor  104  can be adjusted by changing the method of manufacturing an element. 
     When the external terminals  20  and  21  are short-circuited, a short-circuit current flows to generate a potential difference between the negative electrode of the secondary battery  11  and the external terminal  21 . This potential difference is determined based on a current amount I 2  flowing between the external terminals  20  and  21 , the resistance value R 12  of the N-channel discharge control field effect transistor  12 , and the resistance value R 13  of the N-channel charge control field effect transistor  13 , and is represented by I 2 ×(R 12 +R 13 ). The comparator circuit  102  compares the reference voltage V ref  with a voltage of the node of the resistors  106  and  107 . When the voltage of the node of the resistors  106  and  107  is higher, the comparator circuit  102  outputs the detection signal to the control circuit  15  to turn off the N-channel discharge control field effect transistor  12  for short-circuit protection. 
     When a setting value of the short-circuit detection current value is represented by I SHORT , a resistance value of the resistor  106  is represented by R 106 , a resistance value of the resistor  107  is represented by R 107 , and a voltage of the external terminal  21  as a threshold voltage for the comparator circuit  102  to output the detection signal is represented by V ref2 , V ref2 =V ref ×(R 106 +R 107 )/R 106  holds. At this time, the current flowing between the external terminals  20  and  21  is obtained by dividing the voltage of the external terminal  21  by the sum of the resistance values of the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13 , and is represented by I SHORT =V ref2 /(R 12 +R 13 )=V ref ×(R 106 +R 107 )/(R 106 ×(R 12 +R 13 )). 
     Similarly to the case of the overcurrent detection, the resistance value (R 12 +R 13 ) has the secondary battery voltage dependence and the temperature dependence, and hence the length W and the length L of the NMOS transistor  105  and the current value of the constant current circuit  103  are changed, to thereby adjust the secondary battery voltage dependence. Further, in order to adjust the short-circuit detection current value I SHORT , which is represented by V ref ×(R 106 +R 107 )/(R 106 ×(R 12 +R 13 )), the absolute value of the reference voltage V ref  and the resistors  106  and  107  need to be calibrated. Through optimization of the values of the resistors  104 ,  106 , and  107  based on the current value of the constant current circuit  103  so that V ref  is I SHORT ×(R 106 ×(R 12 +R 13 ))/(R 106 +R 107 ), a target value of the short-circuit detection current is adjusted. Further, temperature characteristics of the resistors  104 ,  106 , and  107  can be adjusted by changing the method of manufacturing an element. When the absolute value of V ref  is calibrated, the temperature characteristics of the resistors  104 ,  106 , and  107  need to be optimized so that temperature characteristics of V ref  match with temperature characteristics of the N-channel charge and discharge control field effect transistors. 
     In this manner, the secondary battery voltage dependence and the temperature dependence of the value of the reference voltage of the reference voltage circuit can be adjusted so as to match with the secondary battery voltage dependence and the temperature dependence of the resistance value of the N-channel charge and discharge control field effect transistors. Consequently, the setting value I DOP  of the overcurrent detection current value and the setting value I SHORT  of the short-circuit detection current value can be maintained constant even when the secondary battery voltage or temperature changes. Further, the detection can be performed even without using a reference voltage circuit for short-circuit detection, and hence current consumption can be reduced. 
     Note that, the gate of the NMOS transistor  105  is connected to the positive electrode power supply terminal  42  of the charge and discharge control circuit  14 , but the resistance value of the N-channel charge and discharge control field effect transistors only needs to be changed in response to detection of the secondary battery voltage, and hence the same effect as in the first embodiment can be exerted as long as the gate of the NMOS transistor  105  is connected to a circuit having a secondary battery voltage dependence and the constant current value is adjusted. 
     Further, the N-channel discharge control field effect transistor  12 , the N-channel charge control field effect transistor  13 , and the NMOS transistor  105  are used in the description, but the present invention is not limited to this configuration. It is needless to say that, even when P-channel field effect transistors are used, the NMOS transistor  105  is changed to a PMOS transistor, and the constant current circuit  103  is connected to the negative electrode power supply terminal  43  instead of the positive electrode power supply terminal  44 , a similar operation is enabled. 
     Further, the resistor  104 , the resistor  106 , and the resistor  107  are not limited to the configuration described above, and any impedance element may be used as long as the element has impedance. In addition, it is only necessary that the resistor  106  and the resistor  107  can divide the voltage of the overcurrent detecting terminal  19  and the present invention is not limited to this configuration. 
     As described above, the battery device of the first embodiment can match the secondary battery voltage dependence and the temperature dependence of the overcurrent detection voltage and the short-circuit detection voltage of the charge and discharge control circuit with the secondary battery voltage dependence and the temperature dependence of the N-channel charge and discharge control field effect transistors, to thereby improve the accuracy of the overcurrent detection current value and the short-circuit detection current value of the battery device and enhance the safety of the battery device. Further, current consumption can be reduced because a reference voltage circuit for short-circuit detection is not used. 
     Second Embodiment 
       FIG. 2  is a circuit diagram of a charge and discharge control circuit and a battery device according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that the resistors  106  and  107  are eliminated and a short-circuit current detecting terminal  201  and a resistor  202  are added. 
     Connection in the charge and discharge control circuit and the battery device of this embodiment is described. The inverting input terminal of the comparator circuit  102  is connected to the short-circuit current detecting terminal  201 . The resistor  202  has one terminal connected to the short-circuit current detecting terminal  201  and the other terminal connected to the drain of the N-channel charge control field effect transistor  12 . The remaining connection is similar to that in the first embodiment. 
     Next, an operation of the charge and discharge control circuit and the battery device of this embodiment is described. The second embodiment is similar to the first embodiment in the operation that a load is connected between the external terminals  20  and  21  to detect an overcurrent. When the external terminals  20  and  21  are short-circuited, a short-circuit current flows to generate a potential difference between the negative electrode of the secondary battery  11  and the external terminal  21 . This potential difference is determined based on the current amount I 2  flowing between the external terminals  20  and  21 , the resistance value R 12  of the N-channel discharge control field effect transistor  12 , and the resistance value R 13  of the N-channel charge control field effect transistor  13 , and is represented by I 2 ×(R 12 +R 13 ). The comparator circuit  102  compares the reference voltage of the reference voltage circuit with a voltage of the drain of the N-channel charge control field effect transistor  12 . When the voltage of the drain of the N-channel charge control field effect transistor  12  is higher, the comparator circuit  102  outputs the detection signal to the control circuit  15  to turn off the N-channel discharge control field effect transistor  12  for short-circuit protection. 
     When a setting value of the short-circuit detection current value is represented by I SHORT , a resistance value of the N-channel discharge control field effect transistor  12  is represented by R 12 , a resistance value of the N-channel discharge control field effect transistor  13  is represented by R 13 , a threshold voltage for the comparator circuit  101  to output the detection signal is represented by V ref , and a threshold voltage for the comparator circuit  102  to output the detection signal is represented by V ref2 , V ref2 =V ref ×(R 12 +R 13 )/R 12  holds. Thus, a voltage of the external terminal  21  at the time when the comparator circuit  102  outputs the detection signal is V ref2 . At this time, the current flowing between the external terminals  20  and  21  is obtained by dividing the voltage of the external terminal  21  by the sum of the resistance values of the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13 , and is represented by I SHORT =V ref2 /(R 12 +R 13 )=V ref /R 12 . 
     Similarly to the case of the overcurrent detection, the resistance value R 12  has the secondary battery voltage dependence and the temperature dependence, and hence the length W and the length L of the NMOS transistor  105  and the current value of the constant current circuit  103  are changed, to thereby adjust the secondary battery voltage dependence. Further, in order to adjust the short-circuit detection current value I SHORT , which is represented by V ref /R 12 , the absolute value of the reference voltage V ref  needs to be calibrated. Through optimization of the value of the resistor  104  based on the current value of the constant current circuit  103  so that V ref  is I SHORT ×R 12 , a target value of the short-circuit detection current is adjusted. Further, temperature characteristics of the resistor  104  can be adjusted by changing the method of manufacturing an element. When the absolute value of V ref  is calibrated, the temperature characteristics of the resistor  104  need to be optimized so that temperature characteristics of V ref  match with temperature characteristics of the N-channel charge and discharge control field effect transistors. 
     In this manner, the secondary battery voltage dependence and the temperature dependence of the value of the reference voltage of the reference voltage circuit can be adjusted so as to match with the secondary battery voltage dependence and the temperature dependence of the resistance value of the N-channel charge and discharge control field effect transistors. Consequently, the setting value I DOP  of the overcurrent detection current value and the setting value I SHORT  of the short-circuit detection current value can be maintained constant even when the secondary battery voltage or temperature changes. Further, the detection can be performed even without using a reference voltage circuit for short-circuit detection, and hence current consumption can be reduced. 
     Note that, the gate of the NMOS transistor  105  is connected to the positive electrode power supply terminal  42  of the charge and discharge control circuit  14 , but the resistance value of the N-channel charge and discharge control field effect transistors only needs to be changed in response to detection of the secondary battery voltage, and hence the same effect as in the first embodiment can be exerted as long as the gate of the NMOS transistor  105  is connected to a circuit having a secondary battery voltage dependence and the constant current value is adjusted. 
     Further, the N-channel discharge control field effect transistor  12 , the N-channel charge control field effect transistor  13 , and the NMOS transistor  105  are used in the description, but the present invention is not limited to this configuration. It is needless to say that, even when P-channel field effect transistors are used, the NMOS transistor  105  is changed to a PMOS transistor, and the constant current circuit  103  is connected to the negative electrode power supply terminal  43  instead of the positive electrode power supply terminal  44 , a similar operation is enabled. 
     Further, the N-channel discharge control field effect transistor  12  and the N-channel charge control field effect transistor  13  are not limited to this configuration, and any impedance element may be used as long as the impedance element can be controlled by the signal from the control circuit  15  and has impedance. Those components may be built in the charge and discharge control circuit  14 . 
     Further, the resistor  104  is not limited to the configuration described above, and any impedance element may be used as long as the element has impedance. 
     As described above, the battery device of the second embodiment can match the secondary battery voltage dependence and the temperature dependence of the overcurrent detection voltage and the short-circuit detection voltage of the charge and discharge control circuit with the secondary battery voltage dependence and the temperature dependence of the N-channel charge and discharge control field effect transistors, to thereby improve the accuracy of the overcurrent detection current value and the short-circuit detection current value of the battery device and enhance the safety of the battery device. Further, current consumption can be reduced because a reference voltage circuit for short-circuit detection is not used. 
     Third Embodiment 
       FIG. 3  is a circuit diagram of a charge and discharge control circuit and a battery device according to a third embodiment of the present invention. The third embodiment differs from the battery device of the first embodiment in that a resistor  301  is added between a node of the negative electrode of the secondary battery  11  and the negative electrode power supply terminal  43  and the source of the N-channel discharge control field effect transistor  12 . All the remaining connection is similar to that in the first embodiment. 
     An on-resistance R 12  of the N-channel discharge control field effect transistor  12  and an on-resistance R 13  of the N-channel charge control field effect transistor  13  greatly fluctuate in the manufacturing process and are low in accuracy. To deal with this, a resistor  33 , which has less fluctuations in resistance value than the N-channel field effect transistors, is connected in series to the N-channel field effect transistors. In this manner, the fluctuations in overcurrent detection current value can be reduced. The operations of detecting the overcurrent and the short-circuit current are the same as in the first embodiment, and can be realized also by the configuration of  FIG. 3 . 
     Note that, the position of the resistor  301  is not limited to the position of  FIG. 3 , and the resistor  301  may be connected at any position between the node of the negative electrode of the secondary battery  11  and the negative electrode power supply terminal  43  and a node of the external terminal  21  and the resistor  22 . 
     Further, the resistor  301  may not be a resistor formed by design, and may be a parasitic resistor formed when the circuit is constructed. Further, the configuration of the third embodiment may be used not only for the configuration of the first embodiment but also for the configuration of the second embodiment. 
     As described above, the battery device of the third embodiment can match the secondary battery voltage dependence and the temperature dependence of the overcurrent detection voltage and the short-circuit detection voltage of the charge and discharge control circuit with the secondary battery voltage dependence and the temperature dependence of the N-channel charge and discharge control field effect transistors, to thereby improve the accuracy of the overcurrent detection current value and the short-circuit detection current value of the battery device and enhance the safety of the battery device. Further, current consumption can be reduced because a reference voltage circuit for short-circuit detection is not used.