Patent Document

RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-121036 filed on Jun. 7, 2013, 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 plurality of secondary batteries connected in series, a charge/discharge control circuit equipped with an intermediate terminal disconnection detecting circuit for detecting disconnection with the secondary batteries, and a battery device. 
     2. Background Art 
     In a battery device equipped with a plurality of secondary batteries connected in series, when disconnection (hereinafter called intermediate terminal disconnection) of a connecting portion of each secondary battery and a charge/discharge control circuit occurs, it is not possible to perform charge/discharge control of the secondary batteries. That is, there was a problem that though the secondary batteries were in overcharge or overdischarge, it could not be detected, thus giving large stress to the secondary batteries. Therefore, there has been proposed a battery device equipped with an intermediate terminal disconnection detecting circuit for the purpose of detecting the intermediate terminal disconnection to thereby enhance safety of the secondary batteries. 
     A circuit diagram of a battery device equipped with a related art intermediate terminal disconnection detecting circuit is shown in  FIG. 3 . The battery device includes secondary batteries  107   a  and  107   b , a charge control FET  106 , a discharge control FET  105 , external terminals  112  and  113 , and a charge/discharge control circuit  201 . 
     The charge/discharge control circuit  201  is composed of a positive power supply connection terminal  108  to which a positive power supply of the secondary battery  107   a  is connected, an intermediate terminal  109  connected to a connecting point of a negative power supply of the secondary battery  107   a  and a positive power supply of the secondary battery  107   b , a negative power supply connection terminal  110  to which a negative power supply of the secondary battery  107   b  is connected, a voltage detection circuit  102  for monitoring the voltage between the positive power supply connection terminal  108  and the intermediate terminal  109 , a voltage detection circuit  103  for monitoring the voltage between the intermediate terminal  109  and the negative power supply connection terminal  110 , a control circuit  204  for outputting signals for controlling the charge control FET  106  and the discharge control FET  105  in response to the outputs of the voltage detection circuits  102  and  103 , and an intermediate terminal disconnection detecting circuit  211 . 
     The operation of the related art battery device will next be described. 
     When a voltage generator such as a charger is connected between the external terminals  112  and  113  to charge the secondary batteries  107   a  and  107   b , the voltage detection circuit  102  outputs a detection signal to the control circuit  204  when the voltage of the secondary battery  107   a  reaches a predetermined voltage or higher set by the voltage detection circuit  102 . Then, the control circuit  204  having received the signal therein outputs a signal for turning off the charge control FET  106  to turn off the charge control FET  106  to thereby avoid a charging current from flowing and thereby controls the secondary battery  107   a  so as to prevent its overcharging. 
     When a load such as a resistor is connected between the external terminals  112  and  113  to discharge the secondary batteries  107   a  and  107   b , the voltage detection circuit  102  outputs a detection signal to the control circuit  204  when the voltage of the secondary battery  107   a  becomes a different predetermined voltage or less set by the voltage detection circuit  102 . Then, the control circuit  204  having received the signal therein outputs a signal for turning off the discharge control FET  105  to turn off the discharge control FET  105  to thereby avoid a discharging current from flowing and thereby controls the secondary battery  107   a  so as to prevent its overdischarging. 
     The intermediate terminal disconnection detecting circuit  211  is set to supply more current than the current flowing through the voltage detection circuit  102 . When the connection between the intermediate terminal  109  and the secondary battery  107  is disconnected, the voltage of the intermediate terminal  109  is pulled up by the intermediate terminal disconnection detecting circuit  211 . Accordingly, the difference in voltage between the intermediate terminal  109  and the negative power supply connection terminal  110  becomes large. When it becomes a predetermined voltage or higher set by the voltage detection circuit  103 , the voltage detection circuit  103  detects an intermediate terminal disconnection and outputs its signal to the control circuit  204 . Since the intermediate terminal disconnection can be detected by providing the intermediate terminal disconnection detecting circuit  211  in this manner, it is possible to provide a high safety battery device (refer to, for example, FIG. 1 in Japanese Unexamined Patent Application Publication No. Hei 8(1996)-308115). 
     In the conventional charge/discharge control circuit and battery device, however, a difference occurs between current consumed by the secondary battery  107   a  and current consumed by the secondary battery  107   b  due to the current flowing through the intermediate terminal disconnection detecting circuit  211 . A problem arose in that since this current difference became an unbalance current for each secondary battery to be connected and caused the balance between battery voltages to collapse, the service life of the battery device would be shortened. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised to solve the problems described above, and achieves a charge/discharge control circuit and a battery device capable of detecting an intermediate terminal disconnection without causing the balance between battery voltages to collapse and shortening the service life of the battery device. 
     In order to solve the related art problems, a charge/discharge control circuit and a battery device according to the present invention have the following configuration. 
     There are provided at least, a positive power supply connection terminal, an intermediate terminal and a negative power supply connection terminal respectively connected with a positive electrode terminal, an inter-battery connection terminal and a negative electrode terminal of each of a plurality of secondary batteries connected in series; intermediate terminal disconnection detecting circuits each allowing a detection current to flow by switching at every predetermined time between the positive power supply connection terminal and the intermediate terminal, between the intermediate terminals adjacent to each other and between the intermediate terminal and the negative power supply connection terminal; a plurality of voltage detection circuits respectively connected in parallel with the secondary batteries; a control circuit inputted with outputs of the voltage detection circuits; and an intermediate terminal disconnection control circuit that controls the intermediate terminal disconnection detecting circuits. 
     According to the present invention, the intermediate terminal disconnection detecting circuits are switched by the switches at intervals of constant time to make the same the times during which the intermediate terminal detecting circuits are being connected to the secondary batteries, whereby the time during which an unbalance current for each secondary battery flows becomes the same. As a result, the unbalance current for all the secondary batteries can be cancelled on the time average. Further, it is possible to prevent the balance between battery voltages from being lost and prevent the service life of the battery device from being shortened. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a battery device equipped with a charge/discharge control circuit according to a first embodiment; 
         FIG. 2  is a circuit diagram of a battery device equipped with a charge/discharge control circuit according to a second embodiment; and 
         FIG. 3  is a circuit diagram of a charge/discharge control circuit and a battery device of related art. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a circuit diagram of a battery device equipped with a charge/discharge control circuit according to a first embodiment. The battery device includes secondary batteries  107   a  and  107   b , a charge control FET  106 , a discharge control FET  105 , external terminals  112  and  113 , and a charge/discharge control circuit  101 . The charge/discharge control circuit  101  includes a positive power supply connection terminal  108 , an intermediate terminal  109 , a negative power supply connection terminal  110 , an intermediate terminal disconnection detecting circuit  125 , an intermediate terminal disconnection detecting circuit  118 , a voltage detection circuit  102 , a voltage detection circuit  103 , and a control circuit  104  having an intermediate terminal disconnection control circuit  115 . The intermediate terminal disconnection detecting circuit  125  is composed of a constant current source  111  and a switch  116 . The intermediate terminal disconnection detecting circuit  118  is composed of a constant current source  114  and a switch  117 . 
     The secondary battery  107   a  has a positive power supply connected to the external terminal  112  and the positive power supply connection terminal  108 , and a negative power supply connected to the intermediate terminal  109 . The secondary battery  107   b  has a positive power supply connected to the intermediate terminal  109 , and a negative power supply connected to the negative power supply connection terminal  110  and the discharge control FET  105 . The voltage detection circuit  102  is connected between the positive power supply connection terminal  108  and the intermediate terminal  109 . The voltage detection circuit  103  is connected between the intermediate terminal  109  and the negative power supply connection terminal  110 . The control circuit  104  is inputted with the outputs of the voltage detection circuits  102  and  103 . The outputs of the control circuit  104  are connected to a gate of the charge control FET  106  and a gate of the discharge control FET  105  respectively. The charge control FET  106  and the discharge control FET  105  are connected between the negative power supply of the secondary battery  107   b  and the external terminal  113 . The intermediate terminal disconnection detecting circuit  125  is connected between the positive power supply connection terminal  108  and the intermediate terminal  109 . The intermediate terminal disconnection detecting circuit  118  is connected between the intermediate terminal  109  and the negative power supply connection terminal  110 . 
     The voltage detection circuit  102  monitors the voltage between the positive power supply connection terminal  108  and the intermediate terminal  109 . The voltage detection circuit  103  monitors the voltage between the intermediate terminal  109  and the negative power supply connection terminal  110 . In response to the outputs of the voltage detection circuits  102  and  103 , the control circuit  104  outputs signals for controlling the charge control FET  106  and the discharge control FET  105 . The intermediate terminal disconnection control circuit  115  controls turning-on/off of the switches  116  and  117  by a control signal. The constant current source  111  pulls up the intermediate terminal  109  when the intermediate terminal  109  and each secondary battery are disconnected, i.e., an intermediate terminal disconnection occurs. The constant current source  114  pulls down the intermediate terminal  109  when the intermediate terminal  109  and each secondary battery are disconnected, i.e., an intermediate terminal disconnection occurs. The constant current sources  111  and  114  supply an equal current. 
     The operation of the battery device equipped with the charge/discharge control circuit according to the first embodiment will next be described. 
     When the charge/discharge control circuit  101  is monitoring the voltages of the secondary batteries  107   a  and  107   b , the intermediate terminal disconnection control circuit  115  controls to turn on the switches  116  and  117  alternately for a predetermined time. When the switch  116  is turned on and the switch  117  is turned off, the constant current source  111  is connected between the positive power supply connection terminal  108  and the intermediate terminal  109 . Also, when the switch  116  is turned off and the switch  117  is turned on, the constant current source  114  is connected between the intermediate terminal  109  and the negative power supply connection terminal  110 . 
     When the switch  116  is turned on when the intermediate terminal  109  and each secondary battery are disconnected, i.e., the intermediate terminal disconnection occurs, the intermediate terminal  109  is pulled up by the constant current source  111  so that the difference in voltage between the intermediate terminal  109  and the negative power supply connection terminal  110  becomes large. Accordingly, the voltage detection circuit  103  detects the intermediate terminal disconnection when the inter-terminal voltage becomes a predetermined voltage or higher, and turns off the charge control FET  106 . Further, when the switch  117  is tuned on when the intermediate terminal disconnection occurs, the intermediate terminal  109  is pulled down by the constant current source  114  so that the difference in voltage between the positive power supply connection terminal  108  and the intermediate terminal  109  becomes large. Accordingly, the voltage detection circuit  102  detects the intermediate terminal disconnection when the inter-terminal voltage becomes the predetermined voltage or higher, and turns off the charge control FET  106 . 
     As described above, since the currents of the constant current source  111  and the constant current source  114  are equalized, and the times required to turn on the switches  116  and  117  are set equal, the currents flowing from the second battery  107   a  and the second battery  107   b  become equal to each other, thus making it possible to make equal influences on each secondary battery by the intermediate terminal disconnection detecting circuits. 
     Incidentally, the switches  116  and  117  may be controlled so as to be turned on by providing a period during which the switches  116  and  117  are both turned off, that is, leaving a predetermined interval in between. By controlling the switches in this way, it is possible to further reduce the time during which an unbalance current flows, and cancel the unbalance current on the time average by switching between the switches  116  and  117 . At this time, the predetermined time or interval during which the switches  116  and  117  are turned on may be designed appropriately. 
     Although each intermediate terminal disconnection detecting circuit has been described as having the equal constant current sources and the equal on times, they may be set even in whatever form if the total amounts of detection currents flowing therethrough are equal. 
     The constant current sources are used with the intermediate terminals as pull-up and pull-down means, but are not limited thereto. Further, although a description has been made of the case where the two secondary batteries are connected, the number of secondary batteries is not limited thereto. 
     As described above, the battery device equipped with the charge/discharge control circuit according to the first embodiment is capable of canceling the unbalance current by the intermediate terminal disconnection detecting circuits on the time average and solving imbalance in battery voltage to lengthen the service life of the battery device. 
     Second Embodiment 
       FIG. 2  is a circuit diagram of a battery device equipped with a charge/discharge control circuit according to a second embodiment. An intermediate terminal disconnection detecting circuit  123  employed in the second embodiment includes a constant current source  124  and switches  119 ,  120 ,  121  and  122 . 
     The switch  119  has one terminal connected to the positive power supply connection terminal  108  and the other terminal connected to one terminal of the constant current source  124 . The other terminal of the constant current source  124  is connected to one terminal of the switch  122 . The other terminal of the switch  122  is connected to the negative power supply connection terminal  110 . The switch  121  has one connection terminal connected to a connecting point of the switch  119  and the constant current source  124 , and the other terminal connected to the intermediate terminal  109 . The switch  120  has one connection terminal connected to a connecting point of the switch  122  and the constant current source  124 , and the other terminal connected to the intermediate terminal  109 . 
     The operation of the battery device equipped with the charge/discharge control circuit according to the second embodiment will next be described. 
     When the charge/discharge control circuit  101  is monitoring the voltages of the secondary batteries  107   a  and  107   b , the intermediate terminal disconnection control circuit  115  controls to turn on the switches  119  and  120  and the switches  121  and  122  alternately for a predetermined time. When the switches  119  and  120  are turned on and the switches  121  and  122  are turned off, the constant current source  124  is connected between the positive power supply connection terminal  108  and the intermediate terminal  109 . Also, when the switches  119  and  120  are turned off and the switches  121  and  122  are turned on, the constant current source  124  is connected between the intermediate terminal  109  and the negative power supply connection terminal  110 . 
     When the switches  119  and  120  are turned on when the intermediate terminal  109  and each secondary battery are disconnected, i.e., the intermediate terminal disconnection occurs, the intermediate terminal  109  is pulled up by the constant current source  124  so that the difference in voltage between the intermediate terminal  109  and the negative power supply connection terminal  110  becomes large. Accordingly, the voltage detection circuit  103  detects the intermediate terminal disconnection when the inter-terminal voltage becomes a predetermined voltage or higher, and turns off the charge control FET  106 . Further, when the switches  121  and  122  are turned on when the intermediate terminal disconnection occurs, the intermediate terminal  109  is pulled down by the constant current source  124  so that the difference in voltage between the positive power supply connection terminal  108  and the intermediate terminal  109  becomes large. Accordingly, the voltage detection circuit  102  detects the intermediate terminal disconnection when the inter-terminal voltage becomes the predetermined voltage or higher, and turns off the charge control FET  106 . 
     As described above, since the times during which the switches  119  and  120  and the switches  121  and  122  are turned on are set equal by the common constant current source  124 , and the intermediate terminal disconnection is detected, the currents flowing from the second battery  107   a  and the second battery  107   b  become equal to each other, thus making it possible to make equal influences on each secondary battery by the intermediate terminal disconnection detecting circuit  123 . 
     Incidentally, each switch may be controlled to be turned on with a predetermined interval left therebetween. By controlling the switches in this way, it is possible to further reduce the time during which an unbalance current flows, and cancel the unbalance current on the time average. At this time, the predetermined time or interval during which each switch is turned on may be designed appropriately. 
     Although each intermediate terminal disconnection detecting circuit has been described as having the equal constant current source and the equal on time, it may be set even in whatever form if the total amounts of detection currents flowing therethrough are equal. 
     The constant current source has been used with the intermediate terminal as pull-up and pull-down means, but is not limited thereto. Further, although a description has been made of the case where the two secondary batteries are connected, the number of secondary batteries is not limited thereto. 
     As described above, the battery device equipped with the charge/discharge control circuit according to the second embodiment is capable of canceling the unbalance current by the intermediate terminal disconnection detecting circuit on the time average and solving imbalance in battery voltage to lengthen the service life of the battery device.

Technology Category: 5