Abstract:
A charging and discharging control circuit is provided in which a delay circuit is built in an over-discharge detector circuit, an over-charge detector circuit, or the like. A delay time of the detector circuit can be changed from an external without adding a control terminal, thereby reducing a test time of the detector circuit. A voltage detector circuit is disposed between a power supply terminal and a power supply voltage detection terminal of the charging and discharging control circuit, and the voltage detector circuit detects a specified voltage or higher, to thereby shorten the delay time of the internal control circuit.

Description:
This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2006-009904 filed Jan. 18, 2006, 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 charging and discharging control circuit and a charging type power supply device, and more particularly, to a technique for reducing the amount of time required to perform a test on the charging and discharging control circuit and the charging-type power supply device. 
   2. Description of the Related Art 
   As a conventional charging type power supply device that is formed of a secondary battery, there has been known a power supply device as shown in a circuit block diagram of  FIG. 2  (for example, refer to JP 04-75430 A). That is, a secondary battery  101  is connected to external terminals −V 0  and +V 0  through a switch circuit  102 . Further, a charging and discharging control circuit  110  is connected in parallel to the secondary battery  101 . The function of the charging and discharging control circuit  110  is to detect a voltage across the secondary battery  101 . In a case where the secondary battery  101  is in an over-charging state (a state in which the battery is higher than a given voltage value, hereinafter, called “over-charging protection state”) or in an over-discharging state (a state in which the battery is lower than a given voltage value, hereinafter, called “over-discharging protection state”), a signal is outputted from the charging and discharging control circuit  110  so that the switch circuit  102  turns off. Also, it is possible to stop the discharge (over-current control) when an excessive current is caused to flow in a load in such a manner that the switch circuit  102  turns off when the external terminal +V 0  reaches a given voltage. Hereinafter, this state is called “over-current protection state.” The function of the charging and discharging control circuit is to protect the battery from those states. 
   The switch circuit  102  can be configured by an element capable of stopping the current in response to an input signal from an FET or the like. Also, there is a case in which, as shown in  FIG. 3 , a power supply terminal  10  for supplying a voltage to the charging and discharging control circuit  110 , and a voltage detection terminal  20  for detecting the voltage across the secondary battery  101  are disposed separately. There is also a case in which the power supply terminal of the charging and discharging control circuit  110  is generally connected with a resistor  200  and a capacitor  210  as a filter so that the power supply variation attributable to the charge and discharge of the secondary battery does not induce a malfunction of the charging and discharging control circuit  110 . Even in this case, a power supply terminal  10  is additionally disposed to prevent the current consumption of the charging and discharging control circuit  110  from flowing through the voltage detection terminal  20 . As a result, it is possible to prevent an error from occurring in the detection voltage of the charging and discharging control circuit  110  due to the current consumption and the voltage drop that is caused by the resistor  200 . The above-mentioned configuration makes it possible to enhance a detection precision for detecting a state of the secondary battery  101 . 
   Also, in the case of controlling the charge and discharge of a lithium ion battery, there is generally employed a structure in which, in order to protect the lithium ion battery from being over-charged, a switch element of the switch circuit is turned off after a given delay time that is given by a delay circuit in a case where it is detected that a terminal voltage is equal to or higher than a given level, thereby prohibiting the charge. As a result, the charge into the secondary battery is controlled so that the over-charging state is surely detected and the secondary battery is prevented from being in the over-charging state, without corresponding to a transitional change in the battery voltage. In the charging and discharging control circuit, a control for detecting the over-discharge and stopping the current supply to a load from the secondary battery, and a control for detecting the over-current from the secondary battery to the load and stopping the current supply to the load from the secondary battery are also conducted in the same manner. The delay circuit is used even in the respective controls for the same reason. For example, in order to control the charge and discharge of the lithium ion battery, a delay time of several milliseconds to several seconds is required. 
   However, in a case of a charging and discharging control circuit including a delay circuit therein, a terminal that allows a delay time to be changed from an external may not be prepared due to the limit of the number of terminals provided in the circuit. In this case, when the over-charge detection voltage or the over-discharge detection voltage is tested, it takes a time equal to or longer than the delay time in the respective tests to output an output signal. A time equal to or longer than the respective delay times is required to confirm the output signal, to thereby extend the test time of the charging and discharging control circuit, resulting in an increase in the circuit manufacture costs as well as the manufacturing costs of the charging type power supply device using the charging and discharging control circuit. 
   SUMMARY OF THE INVENTION 
   In view of the above-mentioned circumstances, the present invention has been made to solve the above-mentioned problems, and therefore, it is an object of the present invention to provide a charging and discharging control circuit in which a voltage detector circuit is disposed between a power supply terminal and a voltage detection terminal, and a test mode of shortening a delay time of an internal control circuit is entered in a case where the voltage detector circuit detects a constant voltage or higher between both terminals having normally substantially the same voltage. 
   With the above-mentioned structure, the test time of the charging and discharging control circuit is reduced, thereby making it possible to decrease the manufacturing costs. 
   As described above, the charging and discharging control circuit according to the present invention enters the test mode of reducing the delay time of the internal control circuit without adding a control terminal, thereby obtaining the effect of reducing the test time and decreasing the manufacturing costs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a charging type power supply device including a charging and discharging control circuit according to a first embodiment of the present invention; 
       FIG. 2  is a block diagram showing a conventional charging type power supply device; 
       FIG. 3  is a block diagram showing a conventional charging type power supply device; 
       FIG. 4  is a waveform diagram showing an operation of the charging and discharging control circuit; 
       FIG. 5  is a waveform diagram showing the operation of the charging and discharging control circuit according to the first embodiment of the present invention; 
       FIG. 6  is a block diagram showing a charging type power supply device including a charging and discharging control circuit according to a second embodiment of the present invention; and 
       FIG. 7  is a waveform diagram showing the operation of the charging and discharging control circuit according to the second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A description will now be given in more detail of the preferred embodiments of the present invention with reference to the accompanying drawings. 
   First Embodiment 
   A first embodiment of the present invention is shown in  FIG. 1 .  FIG. 1  is a block diagram showing a charging type power supply device including a charging and discharging control circuit according to the present invention. 
   Hereinafter, the first embodiment will be described with reference to  FIG. 1 . A secondary battery  101  is connected between external power supply terminals +VO and −V 0  through a switch circuit  102 . A charging and discharging control circuit  110  is connected in parallel to the secondary battery  101 . A positive electrode of the secondary battery  101  is connected to a voltage detection terminal  20  of the charging and discharging control circuit  110 , and is connected to a power supply terminal  10  through a resistor  200 . A capacitor  210  is connected between the power supply terminal  10  and a negative electrode of the secondary battery  101  so that the charging and discharging control circuit  110  is not affected by a malfunction or the like due to the temporary power supply variation of the secondary battery  101 . 
   The charging and discharging control circuit  110  includes an over-charging detection comparator  113 , a reference voltage circuit  116  for applying a given reference voltage Vr to an input terminal of the over-charge detection comparator  113 , a voltage divider circuit  111  that divides a voltage across the secondary battery  101 , an internal control circuit  120 , and an internal delay circuit  121 . An on/off control terminal of the switch circuit  102  is connected to a switch control terminal  30  of the charging and discharging control circuit  110 , and an on/off operation of the switch circuit  102  is controlled according to a detection result of the charging and discharging control circuit  110 . 
   A charger  104  for charging the secondary battery  101  or a load  103  that is driven by the secondary battery  101  is connected between the external power supply terminals +VO and −VO. 
   The over-charge detection comparator  113  has a function of comparing a voltage division output resulting from dividing the terminal voltage of the secondary battery  101  by resistors R 0  and R 1  of the voltage divider circuit  111  with a reference voltage Vr of the reference voltage circuit  116  to detect an over-charge state. The over-charge detection comparator  113  has a high-level output when the level of the divided output voltage that is inputted to the positive phase input terminal becomes larger than the reference voltage Vr. The voltage detector circuit  130  monitors a voltage difference between the power supply terminal  10  and the voltage detection terminal  20 , and outputs a detection signal to the internal delay circuit  121  in a case where the potential difference between the power supply terminal  10  and the voltage detection terminal  20  becomes equal to or higher than a given voltage. The internal control circuit  120  inputs the outputs of the over-charge detection comparator  113  and the voltage detector circuit  130  as input signals and outputs a signal to the internal delay circuit  121 . The internal delay circuit  121  inputs the output of the internal control circuit  120  as an input signal, and outputs a signal for controlling the switch circuit  102  to the switch control terminal  30  after a given delay time. 
   When the secondary battery  101  is in the over-charge state, the over-charge detection comparator  113  detects the over-charge state, and the internal control circuit  120  outputs a control signal to the internal delay circuit  121 . In this situation, when the voltages of the power supply terminal  10  and the voltage detection terminal  20  are substantially equal to each other, the internal delay circuit  121  inputs the output voltage of the over-charge detection comparator  113  as an input signal, and outputs a signal for controlling the switch circuit  102  to the switch control terminal  30  after a delay time t 1  that is specified from the viewpoint of the specification as shown in  FIG. 4 . 
   Also, the voltage detector circuit  130  outputs a signal to the internal control circuit  120  when the potential difference between the power supply terminal  10  and the power supply detection terminal  20  is equal to or higher than a given voltage. Upon inputting the signal of the voltage detector circuit  130 , the internal control circuit  120  outputs a control signal that allows the delay time to be shortened to the internal delay circuit  121 . In this situation, when the over-charge detection comparator  113  detects the over-charge state, the internal delay circuit  121  inputs the output voltage of the over-charge detection comparator  113  as an input signal, and outputs a signal for controlling the switch circuit  102  to the switch control terminal  30  after a delay time t 2  that is shorter than the delay time t 1  that has been specified from the viewpoint of the specification.  FIG. 5  shows a signal waveform when the potential difference between the power supply terminal  10  and the power supply detection terminal  20  is equal to or higher than a given voltage. 
   After that, when the potential difference between the power supply terminal  10  and the power supply detection terminal  20  is decreased to the specified voltage or lower, the voltage detector circuit  130  outputs a control signal that allows the delay time of the internal delay circuit  121  to return to the specified length to the internal control circuit  120 , and the internal delay circuit  121  sets the delay time as the normal delay time t 1 . In normal use, because the voltages at the power supply terminal  10  and the power supply detection terminal  20  are substantially the same potential, there is no case in which the test mode is entered at the normal time. 
   The block diagram of  FIG. 1  shows only the over-charge detector circuit and the peripheral circuit, and the over-discharge detector circuit and the over-current detector circuit can be controlled with the same configuration. 
   Also,  FIG. 5  shows that the voltage at the power supply terminal  10  becomes equal to or higher than the voltage at the power supply detection terminal  20  by the specified voltage or higher, but the circuit may be configured such that the delay time is reduced when the voltage at the power supply detection terminal  20  is equal to or higher than the voltage at the power supply terminal  10  by the specified voltage or higher. 
   Second Embodiment 
     FIG. 6  shows a block diagram showing a charging type power supply device including a charging and discharging control circuit according to a second embodiment of the present invention. 
   A latch circuit  140  is disposed between the voltage detector circuit  130  and the internal control circuit  120  in addition to the charging and discharging control circuit according to the first embodiment. With the above-mentioned configuration, it is possible to change the delay time of the internal delay circuit  121  from t 1  to t 2  by only temporarily setting the potential difference between the power supply terminal  10  and the power supply detection terminal  20  to the specified voltage or higher in the pulse fashion. 
   In order to return the delay time of the internal delay circuit  121  from t 2  to t 1 , it is necessary to reset the latch circuit  140 . The reset of the latch circuit  140  can be performed by, for example, employing methods of decreasing the supply voltage, inverting a symbol with respect to a symbol obtained when the potential difference between the power supply terminal  10  and the power supply detection terminal  20  is detected, generating a signal that returns the latch circuit  140  by using the fact that the control signal of the current switch circuit  102  is inverted, or the like. 
   Also,  FIG. 7  shows that the voltage at the power supply terminal  10  becomes equal to or higher than the voltage at the power supply detection terminal  20  by the specified voltage or higher, but the circuit can be configured such that the delay time is reduced when the voltage at the power supply detection terminal  20  is equal to or higher than the voltage at the power supply terminal  10  by the specified voltage or higher.