Abstract:
A power supply control device for controlling power supply to a pair of terminals to which a load is connected, comprising a voltage measuring part for measuring a voltage which has a predetermined relationship with the voltage of the pair of terminals, a short circuit detecting part for detecting whether a short circuit exists between the pair of terminals based on the measured voltage and for making power supply to the pair of terminals stop when existence of a short circuit is detected, and a constant current supplying part for supplying a constant current though the pair of terminals; wherein the short circuit detecting part is configured to detect that the previously detected short circuit is eliminated when the voltage measured by the voltage measuring part is equal to or greater than a predetermined threshold value upon supplying the constant current through the pair of terminals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is related to, claims priority from and incorporates by reference Japanese patent application number 2009-079798, filed on Mar. 27, 2009. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a power supply control device, power supply control method, program, and power supply device. 
         [0004]    2. Description of Related Art 
         [0005]    In one example, JP H07-28532 A (patent reference 1) suggests overload protection of a power supply device. In patent reference 1, it is disclosed that an overload protection circuit stops the supply of power at the time of overload of the power supply device. Note that a general cause of an overload condition of the power supply device is when a load is short-circuited. 
         [0006]    In the overload protection circuit of patent reference 1, in order to detect whether or not the overload is eliminated, the overload condition of the power supply device is confirmed through periodically restarting the power supply by using a timer. When the overload condition of the power supply device is eliminated, the power supply is restarted. 
         [0007]    The overload protection circuit of patent reference 1 confirms the overload condition of the power supply device by periodically restarting the power supply by using a timer. Therefore, confirmation of the overload condition of the power supply device cannot be performed until the occurrence of the periodic time that is set by the timer. In other words, even when the overload condition of the power supply device is eliminated between the periodic times that are set by the timer, the overload protection circuit of patent reference 1 cannot detect that the overload is eliminated. 
         [0008]    Subsequently, with the overload protection circuit of patent reference 1, even though the overload condition of the power supply device has already been eliminated, a state in which restarting of the power supply is delayed occurs because the periodic time of the timer period has not yet occurred. This type of state does not satisfy a user who desires to restart the power supply as soon as possible. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is made in view of the above background. An object of the present invention is to provide a power supply control device, power supply control method, program, and power supply device that can restart the power supply immediately after the overload condition of the power supply device is eliminated. 
         [0010]    According to the first aspect of the invention, it is provided a power supply control device comprising: a short circuit detecting part that determines a short circuit condition of an output side by measuring voltage of a circuit connected in parallel to the output side and having a diode; and a constant current supplying part that supplies constant current in a forward bias direction of the diode of the circuit connected in parallel to the output side and having the diode, wherein the short circuit detecting part determines that the short circuit condition of the output side is eliminated when the voltage of the circuit connected in parallel to the output side and having the diode, that receives the supplied constant current from the constant current supplying part, greater than or equal to a predetermined threshold value. 
         [0011]    According to the second aspect of the invention, it is provided a power supply device comprising: the power supply control device of the present invention; a battery; and a switch that shuts off or connects an output of the battery based on control of the power supply control device, wherein the switch stops the output of the battery when the power supply control device detects the short circuit of the output side, and restores the output of the battery when the power supply control device detects that the short circuit of the output side is eliminated. 
         [0012]    According to the third aspect of the invention, it is provided a method for controlling power supply having a short circuit detecting step that determines a circuit condition of an output side by measuring a voltage of a circuit connected in parallel with the output side and having a diode, comprising: a constant current supply step that supplies a constant current in a forward bias direction of the diode of the circuit connected in parallel to the output side and having the diode; and a determination step to determine whether or not a short circuit of the output side is eliminated when the voltage of the circuit connected in parallel to the output side and having the diode, that receives the supplied constant current by a processing of the short circuit detecting step, is equal to or more than the predetermined threshold value. 
         [0013]    According to the fourth aspect of the invention, it is provided a computer program wherein an information processing device executes the power supply control method according to the present invention by installing it to the information processing device. 
         [0014]    According to the present invention, the power supply can be restarted immediately after the overload condition of the power supply device is eliminated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic view of main structures of a power supply device according to a first embodiment of the present invention. 
           [0016]      FIG. 2  is a schematic view for explaining an operation principle of a power supply control device shown in  FIG. 1  and showing a case in which a load is normal. 
           [0017]      FIG. 3  is a schematic view for explaining an operation principle of a power supply control device shown in  FIG. 1  and showing a case in which a short circuit occurs at a load. 
           [0018]      FIG. 4  is a diagram for explaining a relationship between existence or nonexistence of a short circuit and a voltage value that is measured by a voltage measuring part shown in  FIGS. 2 and 3 . 
           [0019]      FIG. 5  is a schematic view for explaining an operation principle of a power supply control device shown in  FIG. 1  and illustrating a case in which a switch is turned off due to a short circuit. 
           [0020]      FIG. 6  is a schematic view for explaining an operation principle of a power supply control device shown in  FIG. 1  and showing a case in which a short circuit elimination of a load is measured. 
           [0021]      FIG. 7  is a schematic view for explaining an operation principle of a power supply control device shown in  FIG. 1  and showing a case in which short circuit of a load is eliminated. 
           [0022]      FIG. 8  is a diagram for explaining a relationship between existence or nonexistence of a short circuit and a voltage value that is measured by a voltage measuring part shown in  FIGS. 6 and 7 . 
           [0023]      FIG. 9  is a flow diagram for showing an operation order of a power supply control device shown in  FIG. 1 . 
           [0024]      FIG. 10  is a timing chart for showing operation of a power supply control device shown in  FIG. 1 . 
           [0025]      FIG. 11  is a schematic view of main structures of a power supply device according to a second embodiment of the present invention. 
           [0026]      FIG. 12  is a timing chart for showing operation of a power supply control device shown in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Main Structures of Power Supply Device  1  According to First Embodiment of Present Invention 
       [0027]    Main structures of a power supply device  1  according to a first embodiment are explained with reference to  FIG. 1 .  FIG. 1  is a schematic view of the main structures of the power supply device  1 . As shown in  FIG. 1 , the power supply device  1  is configured with a battery  10 , a diode  11 , a switch  12 , a resistor  13 , a resistor  14 , a diode  15 , a terminal  16 , a terminal  17 , ground connection  18 , and a power supply control device  20 . The power supply control device  20  is configured with a short circuit detecting part  21 , a voltage measuring part  22 , and a constant current supplying part  23 . A load  19  is connected to the power supply device  1  via the terminals  16  and  17 . And, the power supply device  1  also has a charge controlling part  41  in order to charge the battery  10 ; however, the explanation thereof is omitted because there is no direct relationship with the explanation below. Note that description and usage of the units, ohm (Ω), volt (V) and ampere (A) are omitted for a resistance value, voltage value, and current value, respectively, in the explanation below. 
         [0028]    The battery  10  is a direct-current [DC] power supply and is, for example, a lithium-ion battery. The diode  11  is a member to prevent reverse current to the battery  10 . The switch  12  is a member that turns ON (start) or OFF (stop) the power supply to the load  19  by the battery  10 . The resistors  13  and  14  are members that generate voltage by a portion of the current that is provided from the battery  10  to branch and flow to the load  9  at a branch point  40  when the switch  12  is in an ON state. The diode  15  is a member to prevent the reverse current from the side of the terminal  16  to the side of the power supply control device  20 . 
         [0029]    The diode  15  has a role to enable constant current “is” to flow to the side of the terminal  16  when the constant current supplying part  23  supplies constant current to the output side because the resistance value r 1  of the resistor  13  is set at a large value. 
         [0030]    The terminal  16  and the terminal  17  are members to which the load  19  is connected. The ground connection  18  is a member to provide ground potential to the power supply device  1 . The load  19  is generally equipment that is driven by the battery  10 . Here, a case in which a short circuit occurs between the terminal  16  and the terminal  17  by the load  19  means that, for example, a user accidentally contacts metal, such as an edge of a screw driver, to the terminals  16  and  17  that are connected to the load  19 . Alternatively, a user could accidentally connect the conductive wires together that are for connecting the terminals  16  and  17  and the load  19 . 
         [0031]    The power supply control device  20  is a member to control the switch  12  when the short circuit is detected or the elimination of the short circuit of the load  19  is detected. The short circuit detecting part  21  of the power supply control device  20  is a member to detect existence or nonexistence of the short circuit of the load  19 . The voltage measuring part  22  of the power supply control device  20  is a member to measure voltage that occurs across the resistors  13  and  14 . The constant current supplying part  23  is a member to supply constant current to a connecting part of the resistors  13  and  14 . Accordingly, constant current is supplied in a forward bias direction of the diode  15  by the constant current supplying part  23 . 
         [0032]    [Regarding Operation Principle of Power Supply Control Device  20 ] 
         [0033]    Next, an operation principle of the power supply control device  20  is explained with reference to  FIGS. 1-8 . First of all, the operation principle for which the power supply control device  20  detects a short circuit is explained with reference to  FIGS. 2-4 . The resistance value of the resistor  13  is r 1 , and the resistance value of the resistor  14  is r 2 . Hereafter, it is explained as “r 1 +r 2 =R.” At this time, it is preferred that the sum R of the resistance value r 1  of the resistor  13  and the resistance value r 2  of the resistor  14  is set as an extremely large value compared to an internal resistance value rL of the load  19  (rL&lt;&lt;R). In other words, when the power is supplied to the load  19  from the battery  10 , the current that is branched to the resistors  13  and  14  from the branch point  40  is not used to drive the load  19 . Therefore, it is preferred that the branched current to the resistors  13  and  14  is extremely small compared to the current that flows toward the load  19 . On the other hand, a voltage value which can be measured by the voltage measuring part  22  is determined to be a predetermined value due to the design of the voltage measuring part  22 . Therefore, the resistance value r 2  of the resistor  14  is set to be a voltage value that is measurable by the voltage measuring part  22 . 
         [0034]    Accordingly, the measurable voltage value for the voltage measuring part  22  is realized by adjusting the resistance value of the resistor  14  because a voltage-dividing circuit configured with the two resistors  13  and  14  is used as discussed above. Because the resistance value of the resistor  13  is also adjusted in addition to the reasons described above, the sum R of the resistance values of the resistors  13  and  14  can be the desired large resistance value. 
         [0035]    The voltage measuring part  22  is displayed by the symbol representing a direct current voltmeter. Moreover, in  FIGS. 2 ,  3 ,  5 ,  6 , and  7 , the diode  11  that does not have a direct relationship with the explanation for the operation principle is omitted in the figures. 
         [0036]    Condition  1 : When the load  19  is normal ( FIG. 2 ): The battery  10  supplies power to the load  19  via the switch  12 , the terminal  16 , and the terminal  17 . In this case, as shown in  FIG. 2 , a portion of the current i 1  (chain lines) that flows in the load  19  by the branch point  40  is branched, and the current (double chain lines) with a current value i 2  flows in the side of the resistors  13  and  14 . A voltage value of “i 2 ×r 2 =v 1 ” occurs at the connecting point of the resistors  13  and  14  by the current with the current value i 2 . Accordingly, the voltage measuring part  22  outputs the voltage value v 1  to the short circuit detecting part  21 . At this time, because the internal resistance value rL of the load  19  becomes an extremely small resistance value (rL&lt;&lt;R) compared to the resistance value R of the resistors  13  and  14 , the current value i 2  becomes an extremely small current value (i 2 &lt;&lt;i 1 ) compared to the current value i 1 . 
         [0037]    Condition  2 : When a short circuit occurs across the load  19  ( FIG. 3 ): When the short circuit occurs across the load  19 , as shown in  FIG. 3 , a resistance value r 0 L of the load  19  becomes almost “0” (r 0 L≈0). Accordingly, the current value i 3  that flows in the load  19  increases compared to the current value i 1  shown in  FIG. 2  (i 3 &gt;i 1 ). On the other hand, because a voltage in the middle of the voltage-dividing circuit configured with the resistors  13  and  14  becomes almost negligible, the voltage measuring part  22  outputs a voltage value “0” to the short circuit detecting part  21 . 
         [0038]    Here, the short circuit detecting part  21 , as shown in  FIG. 4 , can detect that the short circuit has occurred across the load  19  because the short circuit detecting part  21  detects that the voltage value v 1  measured by the voltage measuring part  22  becomes “0,” which is equal to or less than a threshold value Th# 1 . Accordingly, the short circuit detecting part  21  can detect existence or nonexistence of the short circuit of the load  19  based on the voltage value measured by the voltage measuring part  22 . As a result, the short circuit detecting part  21  controls the switch  12  to be in the “OFF” condition. The principles of this short circuit detection and operation to make the switch  12  in the “OFF” condition are the same as a conventional short circuit detecting method. The switch  12  has a switch driving mechanism, which is not shown in figure, that turns the switch ON or OFF by an instruction from the power supply control device  20 . A threshold value Th# 2  is explained later. This threshold value Th# 2  corresponds to a predetermined threshold value discussed in the claims. 
         [0039]    Condition  3 : When the switch  12  is in the “OFF” condition due to the short circuit ( FIG. 5 ): When the short circuit detecting part  21  detects the short circuit that occurs across the load  19 , as shown in  FIG. 3 , the switch  12  is controlled to be in the “OFF” condition. Accordingly, as shown in  FIG. 5 , the power supply device  1  stops the supply of power to the load  19 . At this time, the voltage measuring part  22  outputs a voltage value “0” to the short circuit detecting part  21 . 
         [0040]    Condition  4 : When the elimination of the short circuit of the load  19  is detected ( FIG. 6 ): When the short circuit occurs across the load  19 , and when the switch  12  becomes in the “OFF” condition as shown in  FIG. 5 , the constant current supplying part  23  starts supplying constant current of a current value “is” to the connecting point between the resistor  13  and the resistor  14  as shown in  FIG. 6 . Accordingly, the constant current supplying part  23  supplies the constant current in a forward bias direction of the diode  15 . This current value “is” is, for example, an extremely small current value, such as 10 μA. Because the resistance value r 1  of the resistor  13  is set as sufficiently larger than the internal resistance value of the diode  15 , the constant current of the current value “is” flows to the ground connection  18  via the diode  15 , the terminal  16 , the load  19 , and the terminal  17 . Due to the constant current of the current value “is”, a voltage value, “is×(internal resistance of the diode  15 )=v 2 ,” occurs at the diode  15 . It is preferred that the resistance value r 1  of the resistor  13  is a few thousand times more than the internal resistance value of the diode  15 . Accordingly, the voltage measuring part  22  outputs the voltage value v 2  to the short circuit detecting part  21 . And, the voltage value v 2  corresponds to the forward direction voltage drop (Vf) of the diode  15 . 
         [0041]    Condition  5 : When the short circuit of the load  19  is eliminated ( FIG. 7 ): When the short circuit that occurs across the load  19  is eliminated, as shown in  FIG. 7 , the load  19  returns to the normal resistance value rL, or the load  19  becomes connected. Because the resistance value r 0 L≈0, rL&gt;&gt;r 0 L. Accordingly, current with a current value i 4  flows in the resistor  14 . Then, a voltage value, “i 4 ×r 2 =v 3 ,” occurs at the resistor  14 . The current of the current value i 4  that flows in the resistor  14  is equal to the constant current of the current value “is” when an output side is in an open condition. Therefore, the voltage measuring part  22  outputs the voltage value v 3  to the short circuit detecting part  21 . In  FIG. 7 , a current value i 5  that flows in the load  19  becomes i 5 =(is−i 4 ). 
         [0042]    Here, in the short circuit detecting part  21 , as shown in  FIG. 8 , the threshold value Th# 2  is set. The threshold value Th# 2  is set as “v 2 ≦Th# 2 ” when the load  19  is short-circuited. And, when the short circuit of the load  19  is eliminated, the threshold value Th# 2  is set as “v 3 &gt;Th# 2 .” Further, the value is higher compared to the threshold value Th# 1  that is explained in  FIG. 4 . In other words, the threshold value Th# 1  that is explained in  FIG. 4  is appropriate when it is higher than a voltage value “0.” In contrast, the threshold value Th# 2  of  FIG. 8  must be higher than the voltage value v 2  (=Vf). 
         [0043]    As discussed above, the short circuit detecting part  21  can detect the elimination of the short circuit of the load  19  based on a voltage value that is measured by the voltage measuring part  22 . The short circuit detecting part  21  that detects the elimination of the short circuit of the load  19  controls to change the switch  12  to be in the “ON” condition. Accordingly, the power supply device  1  returns to the condition shown in  FIG. 2  again. And, at this time, the constant current with the current value “is” supplied by the constant current supplying part  23  is stopped. 
         [0044]    Accordingly, the power supply control device  20  can perform the ON/OFF control for the switch  12  by detecting the occurrence of the short circuit and the elimination of the short circuit of the load  19 . 
         [0045]    An order of operation of the power supply control device  20  described above is shown in a flow diagram of  FIG. 9 . 
         [0046]    START: The power supply control device  20  shifts to the processing of S 1  when the power supply device  1  starts to operate. The term, “the power supply device  1  starts to operate,” means that the activation switch (not shown) of the power supply device  1  is in the “ON” condition. Or it means that the battery  10  is mounted on the power supply device  1 . 
         [0047]    S 1 : The short circuit detecting part  21  determines whether or not a voltage value that is measured by the voltage measuring part  22  is equal to or less than the threshold value Th# 1 . The short circuit detecting part  21  repeats the processing of S 1  when the voltage value that is output from the voltage measuring part  22  is v 1 , which is higher than the threshold value Th# 1  that determines whether or not the short circuit occurs (NO at S 1 ). On the other hand, the short circuit detecting part  21  shifts to the processing of S 2  when a voltage value that is output from the voltage measuring part  22  is “0,” which is equal to or less than the threshold value Th# 1  (YES at S 1 ). 
         [0048]    S 2 : The short circuit detecting part  21  controls the switch  12  to be in the “OFF” condition when the short circuit detecting part  21  determines that the load  19  is in the short circuit condition, and then shifts to the processing of S 3 . 
         [0049]    S 3 : The short circuit detecting part  21  instructs the constant current supplying part  23  to start the constant current supply and shifts to the processing of S 4 . 
         [0050]    S 4 : The constant current detecting part  21  determines whether or not a voltage value that is output from the voltage measuring part  22  is equal to or more than the threshold value Th# 2 . The short circuit detecting part  21  repeats the processing of S 4  when the voltage value that is output from the voltage measuring part  22  is less than the threshold value Th# 2  (NO at S 4 ). On the other hand, the short circuit detecting part  21  shifts to the processing of S 5  when the voltage value that is output from the voltage measuring part  22  is equal to or more than the threshold value Th# 2  (YES at S 4 ). 
         [0051]    S 5 : The short circuit detecting part  21  controls the switch  12  to be in the “ON” condition by determining that the short circuit condition of the load  19  is eliminated. And, the short circuit detecting part  21  also instructs the constant current supplying part  23  to stop the constant current supply and return to the processing of S 1 . 
         [0052]    Subsequently, operation of the power supply control device  20  is shown in  FIG. 10  as a timing chart. In  FIG. 10 , a measured voltage value measured by the voltage measuring part  22 , switch control performed by the short circuit detecting part  21 , and constant current supply performed by the constant current supplying part  23  are described. Moreover, as a reference, a terminal voltage of the terminals  16  and  17  is also described. 
         [0053]    T 1 : No Short Circuit: The voltage measuring part  22  outputs the voltage value v 1 . At this time, because the short circuit detecting part  21  does not detect a short circuit, the switch  12  is in the “ON” condition. Also, the short circuit detecting part  21  does not instruct the constant current supplying part  23  to provide a constant current supply. Further, a voltage value of the terminals  16  and  17  is vT. 
         [0054]    T 2 : Short Circuit Occurs: The voltage measuring part  22  outputs the voltage value “0.” The short circuit detecting part  21  detects the short circuit because the voltage value “0,” which is lower than the threshold value Th# 1 , is output from the voltage measuring part  22 . Here, when the short circuit condition is determined, it is preferred that time shifting the switch  12  in the “OFF” condition is fast because it is necessary to protect the battery (power supply)  10 . For example, it is preferred that the time shifting of the switch  12  in the “OFF” condition is equal to or less than 500 microseconds (hereafter, μsec). At this time, at the short circuit detecting part  21 , a short monitoring time is provided because an instantaneous short circuit which has no influence on the battery  10  should be ignored. The monitoring time is, for example, 250 μsec. Also, the voltage value of the terminals  16  and  17  becomes “0.” As a result, it is preferred that the time shifting the switch  12  in the “OFF” condition is, for example, equal to or less than 250 μsec-500 μsec. 
         [0055]    T 3 : Perform Switch “OFF” Control, Start Constant Current Supply: The short circuit detecting part  21  controls the switch  12  in the “OFF” condition when the monitoring time has elapsed (for example, 250 μsec). The short circuit detecting part  21  controls the switch  12  in the “OFF” condition and instructs the constant current supplying part  23  to supply constant current. The constant current supplying part  23  starts supplying the constant current after the constant current supplying part  23  receives an instruction from the short circuit detecting part  21 . And, the voltage value of the terminals  16  and  17  at this time remains “0.” 
         [0056]    T 4 : Short Circuit Continues: In the condition in which the short circuit of the load  19  continues, at the diode  15 , the voltage value v 2  that is equivalent to the forward direction voltage drop Vf of the diode  15  continues to occur due to the constant current that is supplied by the constant current supplying part  23  in the forward bias direction of the diode  15 . The voltage measuring part  22  outputs the voltage value v 2  to the short circuit detecting part  21 . When the short circuit detecting part  21  compares the voltage value v 2  from the voltage measuring part  22  with the threshold value Th# 2 , the short circuit detecting part  21  determines that the short circuit is not eliminated because the voltage value v 2  is less than the threshold value Th# 2 . The voltage value of the terminals  16  and  17  at this time remains as “0.” 
         [0057]    T 5 : Detect Short Circuit Elimination: When the short circuit of the load  19  is eliminated, the constant current that is provided by the constant current providing part  23  flows in the side of the resistor  14 . Accordingly, the voltage measuring part  22  outputs the voltage value v 3  that is equal to or more than the threshold value Th# 2  to the short circuit detecting part  21 . When the short circuit detecting part  21  compares the voltage value v 3  with the threshold value Th# 2 , the short circuit detecting part  21  detects the short circuit elimination because the voltage value v 3  (V) is equal to or more than Th# 2 . At this time, at the short circuit detecting part  21 , a short monitoring time is provided because an instantaneous short circuit elimination should be ignored. This monitoring time is, for example, 250 microseconds (hereafter, μsec). The voltage value vt of the terminals  16  and  17  becomes “(i 5 ×rL).” 
         [0058]    T 6 : Perform Switch “ON” Control, Stop Constant Current Supply: The short circuit detecting part  21  not only controls the switch  12  in the “ON” condition, but also instructs the constant current supplying part  23  to stop the constant current supply when the monitoring time (for example 250 μsec) has elapsed. The constant current supplying part  23  stops supplying the constant current when the constant current supplying part  23  receives instructions for stopping the constant current supply from the short circuit detecting part  21 . 
         [0059]    Accordingly, the power supply device  1  can immediately restart the power supply to the load  19  when the short circuit of the load  19  is eliminated. This satisfies a request for a user who wishes to restart the power supply as fast as possible. And, as shown in the overload protection circuit described in patent reference 1, when the elimination of the short circuit is determined by periodically returning the switch  12  in the “ON” condition, a large amount of current flows from the battery  10  for a short period of time in the case in which the short circuit is not eliminated. This will cause the capacity of the battery  10  to be rapidly lowered. As the power supply device  1  detects the elimination of the short circuit by a small amount of constant current (for example 10 μA), the capacity of the battery  10  lowered by the short circuit detection can be avoided. 
       Regarding Main Structures of Power Supply Device  1 A of Second Embodiment of Present Invention 
       [0060]    The main structures of a power supply device  1 A of a second embodiment are explained with reference to  FIG. 11 .  FIG. 11  shows a diagram of the main structures of a power supply device  1 A. The part of the structure of the power supply device  1 A is different from the power supply device  1 . Hereafter, same or similar types of numbers are used for the members that are the same or of the same type as the first embodiment, and the explanation thereof is omitted or simplified, and only different members are primarily, explained. 
         [0061]    The power supply device  1 A does not have the resistor  13  and the resistor  14  that exist in the power supply device  1 . The power supply device  1 A has a power supply control device  20 A. The power supply control device  20 A has a short circuit detecting part  21 A, a voltage measuring part  22 A, and a constant current supplying part  23 A. 
         [0062]    The processing and operation of the short circuit detecting part  21 A are same as the short circuit detecting part  21  of the first embodiment. 
         [0063]    The constant current supplying part  23 A continuously supplies the constant current of a current value “is” in the forward bias direction of the diode  15  during operation of the power supply device  1 A. Accordingly, the power measuring part  22 A measures a voltage value that occurs by internal resistance of the diode  15  and the load  19 , and constant current of the current value “is” that is supplied in the forward bias direction of the diode  15  by the constant current supplying part  23 A. 
         [0064]    [Regarding Principle of Power Supply Control Device  20 A] 
         [0065]    Subsequently, an operation principle of the power supply control device  20 A is explained with reference to  FIG. 12 . When the load  19  is normal (no short circuit) (T 1  of  FIG. 12 ), the voltage measuring part  22 A measures the voltage value v 1 A that occurs by the internal resistance of the diode  15  and the load  19 , and the constant current of the current value “is” that is supplied in the forward bias direction of the diode  15  by the constant current supplying part  23 A. 
         [0066]    A measurement result of the voltage measuring part  22 A is outputted to the short circuit detecting part  21 A. The short circuit detecting part  21 A determines that the load  19  is normal (no short circuit) when the measurement result of the voltage measuring part  22 A is the voltage value v 1 A. 
         [0067]    Here, when a short circuit occurs across the load  19  (T 2  of  FIG. 12 ), the side of the diode  15  at the branch  41  reaches the same potential as the ground connection  18 . Accordingly, the voltage value that is measured by the voltage measuring part  22 A becomes the voltage value v 2 , which corresponds to the forward direction voltage drop Vf of the diode  15  that occurs by the internal resistance of the diode  15  and the constant current that is provided by the constant current supplying part  23 A with respect to the forward bias direction of the diode  15 . 
         [0068]    The short circuit detecting part  21 A detects the short circuit across the load  19  after the measurement results of the voltage measuring part  22 A becomes the voltage value v 2 , and controls the switch  12  in the “OFF” condition (T 3  of  FIG. 12 ). The short circuit detecting part  21 A remains in a standby mode while keeping the switch  12  as in the “OFF” condition because the short circuit still continues while the measurement result of the voltage measuring part  22 A is the voltage value v 2  (T 4  of  FIG. 12 ). 
         [0069]    Here, when the short circuit of the load  19  is eliminated, the voltage measuring part  22 A again measures the voltage value v 1 A that occurs by the internal resistance of the diode  15  and the load  19 , and the constant current of the current value “is” that is supplied by the constant current supplying part  23 A with respect to the forward bias direction of the diode  15 . The short circuit detecting part  21 A detects that the short circuit is eliminated after the measurement result of the voltage measuring part  22 A returns to the voltage value v 1 A (T 5  of  FIG. 12 ). 
         [0070]    The short circuit detecting part  21 A controls the switch  12  to be in the “ON” condition when the short circuit is eliminated (T 6  of  FIG. 12 ). 
         [0071]    A flow diagram showing an operation order of the power supply control device  20 A is the same as the flow diagram showing the operation order of the power supply control device  20  except for the deletion of S 3  for “start constant current supply.” In other words, in the power supply control device  20 A, the constant current is constantly supplied with respect to the forward bias direction of the diode  15  during operation of the power supply device  1 A. Because of this, the processing of S 3  of  FIG. 9  is not necessary. Note that v 1  shown in  FIG. 4  is switched to v 1 A in the second embodiment. Also, v 3  shown in  FIG. 8  is switched to v 1 A in the second embodiment. 
       Embodiments Using IC and Program 
       [0072]    It is explained that the power supply control device  20  is configured with three function blocks, the short circuit detecting part  21 , the voltage measuring part  22 , and the constant current supplying part  23 ; however, it can also be realized by forming one electronic circuit that has these functions in the form of an Integrated Circuit (hereafter, IC). 
         [0073]    Alternatively, the short circuit detecting part  21 , the voltage measuring part  22 , and the constant current supplying part  23  of the power supply control device  20  may be configured with a general information processing device (such as a central processing unit (CPU), digital signal processor (DSP), microprocessor (microcomputer), or the like) that are operated by a predetermined program. For example, the general information processing device includes a memory, a CPU, input/output port or the like. A CPU of the general information processing device reads a control program as a predetermined program from memory or the like and executed. By doing this, functions of the short circuit detecting part  21 , the voltage measuring part  22 , and the constant current supplying part  23  of the power supply control device  20  are realized on the general information processing device. 
         [0074]    The control program which is executed by the general information processing device can be stored in a memory or the like of the general information processing device either before shipment of the power supply control device  20  or after shipment of the power supply control device  20 . It is also appropriate that a part of the control program is stored in the memory or the like of the general information processing device after the power supply control device  20  is shipped. The control program that is stored in the memory or the like of the general information processing device after the power supply control device  20  is shipped, for example, can be done by installing a program that is stored in a recording medium readable by a computer, such as CD-ROM, or by installing the program downloaded via a transferring medium, such as the Internet. 
         [0075]    The control program includes a program that is directly executable by the general information processing device, but also includes a program that is executable by installing it in a hard disk. And, the program can be compressed or encrypted. 
         [0076]    As mentioned above, since the power supply control device  20  can be made to be compact by forming it with IC or general information processing devices (CPU, DSP, microprocessor (microcomputer) or the like), it can be assembled inside of the battery pack that contains the battery  10 . 
         [0077]    Accordingly, the power supply device  1 , having a compact structure which can be contained in the battery pack, stops the supply of power when an overload condition of the power supply device  1  is detected, and immediately restarts the supply of power when the overload condition of the power supply device is eliminated, can be realized. 
       Other Embodiments 
       [0078]    The embodiments of the present invention can be modified in various ways so long as not to be regarded as a departure from the sprit and scope of the invention. For example, in the flow diagram of  FIG. 9 , the processing to determine whether or not the voltage value of S 1  is equal to or less than the threshold value Th# 1  may be modified to determine whether or not the voltage value is lower than the threshold value Th# 1 . Also, the processing to determine whether or not the voltage value of S 4  is equal to or more than the threshold value Th# 2  may be modified to determine whether or not the voltage value exceeds the threshold value Th# 2 . 
         [0079]    Even when the constant current that is supplied by the constant current supplying part  23  according to the first embodiment constantly flows during the operation of the power supply device  1 , the influence to the life of the battery  10  is small since the current value is extremely small. Therefore, the constant current supplied by the constant current supplying part  23  may constantly flow during the operation of the power supply device  1  of the first embodiment as in the second embodiment. In this case, the processing of S 3 , “start constant current supply,” in the flow diagram of  FIG. 9  is deleted. 
         [0080]    In this case, when the short circuit of the load  19  occurs as shown in  FIG. 3 , the output of the voltage measuring part  22  does not become “0.” In other words, when the short circuit occurs across the load  19 , as the constant voltage from the constant voltage supply part  23  is supplied to the forward bias direction of the diode  15 , the voltage shown in the voltage measuring part  22  is v 2  (=Vt). In this case, as the current value “is” is extremely small, the relationship of “the threshold value Th# 2 &gt;the threshold value Th# 1 ” does not change. 
         [0081]    The power supply control device, the power supply control method, the program, and the power supply device being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the sprit and scope of the invention, and all such modifications as would be apparent to one of ordinary skill in the art are intended to be included within the scope of the following claims.