Abstract:
A power supply apparatus supplies a power supply voltage to a charge monitor that monitors charge states of rechargeable battery cells. The apparatus includes: a first capacitative element that supplies a power supply voltage to the charge monitor; a second capacitative element that is charged from the rechargeable battery cell and charges the first capacitative element; a switch group including a first switch that connects the first and second capacitative elements, and a second switch that connects the rechargeable battery cell and the second capacitative element; and a controller that controls the switch group. The controller repeats charging the second capacitative element by the rechargeable battery cell by connecting the rechargeable cell and the second capacitative element by the first switch, and charging the first capacitative element by the second capacitative element by connecting the first and second capacitative elements by the second switch.

Description:
BACKGROUND 
     The present disclosure relates to a power supply apparatus, a charging method, a rechargeable battery cell unit, and a charging apparatus. 
     Charging apparatuses such as lithium-ion battery packs that can be repeatedly charged and discharged have been known. Some of these charging apparatuses have a configuration in which rechargeable battery cell units, each of which is formed of a plurality of rechargeable battery cells connected in series, are connected in series. When the charging apparatus is charged and discharged, each of the rechargeable battery cells is also charged and discharged, and thus a charge state of each cell changes. When the charging and discharging are repeated, each of the rechargeable battery cells begins to exhibit a different charge state. If the charging and discharging are continuously repeated in a charge state that varies from one cell to another, the life of the rechargeable battery cells will be shortened. Japanese Patent Document No. 3829453 discloses a method of prolonging the life of rechargeable battery cells by monitoring a charge state of each rechargeable battery cell and controlling, in accordance with the charge state, the charging and discharging of a charging apparatus. 
     In order to achieve downsizing and cost reduction of a monitoring circuit that monitors a charge state of each rechargeable battery cell, there has been a need to manufacture a monitoring circuit as a large scale integrated (LSI) circuit. To manufacture an LSI monitoring circuit, it is necessary to configure a circuit with, for example, a low-voltage metal-oxide semiconductor (MOS) transistor. If the monitoring circuit is configured as a low-voltage circuit, a voltage to be supplied to the monitoring circuit has to be a low voltage. In order to comply with this, Japanese Patent Application Laid-open No. 2010-124597 discloses a configuration in which the voltage of a rechargeable battery cell unit is reduced in order to supply a stepped-down power supply voltage to a low-voltage driven monitoring circuit. 
     SUMMARY 
     As disclosed in Japanese Patent Application Laid-open No. 2010-124597, in a case where a stepped-down power supply voltage is supplied to a monitoring circuit after stepping down the voltage of a rechargeable battery cell unit, a step-down circuit such as a DC-DC converter or a series regulator has to be provided. 
     In a case where the voltage of a rechargeable battery cell unit is stepped down by means of a DC-DC converter, it is necessary to make use of an external coil or a large-capacity capacitor. This results in, for example, an increase in the number of components or mounting area for them, thereby making the realization of the LSI monitoring circuit difficult. 
     In a case where a series regulator is used, the LSI monitoring circuit is manufactured easier in comparison with a case where a DC-DC converter is used, but a problem arises in which a difference between an output voltage (a power supply voltage) and a voltage of a rechargeable battery cell unit, which is a supply source, becomes a power loss as it is. This leads to an increase in power consumption. For example, when using a rechargeable battery cell unit, in which 16 pieces of 3 V rechargeable battery cells are connected in series, the rechargeable battery cell unit being the supply source has a total output voltage of 48 V. In this case, when the monitoring circuit consumes 5 mA at a power supply of 3 V after stepping down the voltage of a rechargeable battery cell unit, then (48 V−3 V)×5 mA=225 mW is consumed at a step-down circuit. In this way, the use of a series regulator causes higher power consumption and hampers energy efficiency. When this consumed electric power is converted into heat, heat related problems also arise. 
     In view of the circumstances as described above, there is a need for a power supply apparatus and a charging method that are capable of supplying a monitoring circuit with a power supply voltage with low power consumption. 
     There is also a need for a rechargeable battery cell unit and a charging apparatus that include such a power supply apparatus. 
     According to an embodiment of the present disclosure, there is provided a power supply apparatus, configured to supply a power supply voltage to a charge monitor configured to monitor a charge state of each of a plurality of rechargeable battery cells, the apparatus including: 
     a first capacitative element configured to supply a power supply voltage to the charge monitor; 
     a second capacitative element configured to be charged from at least one of the rechargeable battery cells and charge the first capacitative element; 
     a switch group including
         a first switch configured to connect the first capacitative element and the second capacitative element to each other, and   a second switch configured to connect the at least one of the rechargeable battery cells and the second capacitative element to each other; and       

     a controller configured to control the switch group, the controller being further configured to repeat
         first control of charging the second capacitative element by the at least one of the rechargeable battery cells by connecting the at least one of the rechargeable cells and the second capacitative element to each other by the first switch, and   second control of charging the first capacitative element by the second capacitative element by connecting the second capacitative element and the first capacitative element to each other by the second switch.       

     By charging the first capacitative element from the rechargeable battery cell via the second capacitative element using the second capacitative element as a charge pump, the first capacitative element can be charged with low power consumption. With this configuration, a power supply voltage can be supplied to a monitoring circuit with low power consumption. 
     According to another embodiment of the present disclosure, there is provided a charging method of charging a first capacitative element of a power supply apparatus configured to supply to a charge monitor configured to monitor a charge state of each of a plurality of rechargeable battery cells a power supply voltage charged to the first capacitative element, the method including: charging a second capacitative element from at least one of the rechargeable battery cells by connecting the at least one of the rechargeable battery cells and the second capacitative element to each other to each other; and charging the first capacitative element from the second capacitative element by connecting the second capacitative element and the first capacitative element to each other, the first capacitative element being charged by repeating the charging of the second capacitative element and the charging of the first capacitative element. 
     According to another embodiment of the present disclosure, there is provided a rechargeable battery cell unit including a plurality of rechargeable battery cells, a charge monitor configured to monitor a charge state of each of the plurality of rechargeable battery cells, and the above-mentioned power supply apparatus configured to supply a power supply voltage to the charge monitor. 
     According to another embodiment of the present disclosure, there is provided a charging apparatus including a plurality of rechargeable battery cell units described above. 
     According to the present disclosure, a power supply voltage can be supplied to a monitoring circuit with low power consumption. 
     These and other objects, features and advantages of the present disclosure will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a charging apparatus according to a first embodiment of the present disclosure; 
         FIG. 2  shows a rechargeable battery module according to the first embodiment; 
         FIG. 3  shows the rechargeable battery module according to the first embodiment; 
         FIG. 4  shows a timing chart showing operation of a power supply apparatus according to the first embodiment; 
         FIGS. 5A and 5B  show the power supply apparatus at the time of charging operation during activation according to the first embodiment; 
         FIG. 6  shows a flowchart showing a process of charging operation during activation according to the first embodiment; 
         FIGS. 7A and 7B  show the power supply apparatus during normal charging processing according to the first embodiment; 
         FIGS. 8A and 8B  show the power supply apparatus during normal charging processing according to the first embodiment; 
         FIG. 9  shows a flowchart showing upper limit monitoring processing according to the first embodiment; 
         FIG. 10  shows a flowchart showing lower limit monitoring processing according to the first embodiment; 
         FIG. 11  shows a power supply monitor according to the first embodiment; 
         FIG. 12  shows a flowchart showing the upper limit monitoring processing according to a modification of the first embodiment; 
         FIG. 13  shows the power supply apparatus during the upper limit monitoring processing according to the modification of the first embodiment; 
         FIGS. 14A and 14B  show a rechargeable battery module according to a second embodiment of the present disclosure; 
         FIG. 15  shows a rechargeable battery module according to a third embodiment of the present disclosure; 
         FIGS. 16A and 16B  show a power supply apparatus at the time of charging operation during activation according to the third embodiment; 
         FIGS. 17A and 17B  show the power supply apparatus during normal charging processing according to the third embodiment; 
         FIGS. 18A and 18B  show the power supply apparatus during normal charging processing according to the third embodiment; 
         FIG. 19  shows a rechargeable battery module according to a fourth embodiment of the present disclosure; 
         FIG. 20  shows a rechargeable battery module according to a fifth embodiment of the present disclosure; and 
         FIG. 21  shows a rechargeable battery module according to a sixth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  shows a charging apparatus  1  according to a first embodiment of the present disclosure. The charging apparatus  1  has a plurality of rechargeable battery modules  10  and a charge monitoring controller  3 . Each of the plurality of rechargeable battery modules  10  has a charge monitoring module  11  and a rechargeable battery cell unit  12 . The plurality of rechargeable battery modules  10  are also collectively referred to as a charging unit  2 . 
     The plurality of rechargeable battery modules  10  are connected to the charge monitoring controller  3  by means of signal lines such as bus lines. The charge monitoring controller  3  instructs each charge monitoring module  11 , for example, to start or end monitoring of each rechargeable battery cell unit  12 , for example. On the basis of a notice of a charge state of each rechargeable battery cell unit  12  from the charge monitoring module  11 , the charge monitoring controller  3  determines whether or not to charge the charging apparatus  1  or notifies an external apparatus (not shown in figures) of a charge state of the charging apparatus  1 . 
     Next, details of the rechargeable battery modules  10  will be explained with reference to  FIG. 2 . The rechargeable battery cell unit  12  of each of the rechargeable battery modules  10  has a plurality of rechargeable battery cells C 1 , C 2 , . . . , C 16 . The rechargeable battery cells C 1 , C 2 , . . . , C 16  are secondary battery cells such as a lithium ion battery cell that can be charged and discharged repeatedly. 
     The rechargeable battery cells C 1 , C 2 , . . . , C 16  are connected in series from a side of a negative terminal V− of the rechargeable battery cell unit  12  in the stated order. Each of these rechargeable battery cells has a center electric potential of 3.2 V, a lower limit electric potential of 2.5 V, and an upper limit electric potential of 4 V. These electric potentials of the rechargeable battery cells and the number of connected rechargeable battery cells (16 cells in this embodiment) are given as examples. Other voltage range and the number of connected rechargeable battery cells may be adopted. 
     The charge monitoring module  11  has a charge monitor  110  and a power supply apparatus  100  that supplies a power supply voltage to the charge monitor  110 . 
     The charge monitor  110  has a measurement cell selector  111  that selects a rechargeable battery cell to measure a charge state thereof, an analog-to-digital converter (ADC)  112  that converts the voltage of a rechargeable battery cell selected by the measurement cell selector  111  into a digital voltage signal, and a logic circuit  113  that performs signal processing on the voltage signal output by the ADC  112  and outputs the measured charge state to the charge monitoring controller  3 . 
     The measurement cell selector  111  has a plurality of switches (not shown in figures). For example, this selector selects a rechargeable battery cell to be measured by turning these switches on and off in accordance with an instruction from the logic circuit  113 . The ADC  112  and the logic circuit  113  are low-voltage circuits formed of, for example, metal oxide semiconductor (MOS) transistors. Both the ADC  112  and the logic circuit  113  operate based on a power supply voltage supplied by the power supply apparatus  100 . Components of the charge monitor  110 , such as the ADC  112  and the logic circuit  113  that operate at a low voltage, are collectively referred to as a “low-voltage circuit.” In this embodiment, the explanation is given on the assumption that a maximum working voltage is 3.6 V and a minimum working voltage of the low-voltage circuit is 2.7 V. 
     The power supply apparatus  100  has a power supply monitor  101 , a cell selector  102 , a first switch SW 1  and a second switch SW 2 , and a first capacitor C_V and a second capacitor C_f. 
     Both the power supply apparatus  100 , excluding the first capacitor C_V and the second capacitor C_f, and the charge monitor  110  (an area surrounded by the dashed-dotted line in  FIG. 2 ) can be formed of, for example, MOS transistors and easily realized in the form of an LSI. 
     The power supply apparatus  100  will be explained in detail with reference to  FIG. 3 . This figure illustrates a rechargeable battery module  10 . For the sake of simplification, the measurement cell selector  111  will be omitted in the figure. 
     The cell selector  102  is constituted of a plurality of switches. The cell selector  102  has low switches SL 0  to SL 15  for selection of negative terminals of respective rechargeable battery cells and high switches SH 1  to SH 16  for selection of positive terminals of respective rechargeable battery cells. 
     Ends on one side of the low switches SL 0  to SL 15  are connected to negative terminals of rechargeable battery cells in the stated order from the negative terminal V− and ends on the other side of the low switches SL 0  to SL 15  are connected to one end of the second capacitor C_f. For example, one end of the low switch SL 0  is connected to a negative terminal of the rechargeable battery cell C 1  and the other end of the low switch SL 0  is connected to the one end of the second capacitor C_f. One end of the low switch SL 1  is connected to a negative terminal of the rechargeable battery cell C 2  and the other end of the low switch SL 1  is connected to the one end of the second capacitor C_f. In this way, the low switches SL 0  to SL 15  are respectively connected to the negative terminals of the rechargeable battery cells C 1  to C 16  connected in series. 
     Ends on one side of the high switches SH 1  to SH  16  are connected to positive terminals of rechargeable battery cells in the stated order from a side of the negative terminal V−, and ends on the other side of the high switches SH 1  to SH  16  are connected to the other end of the second capacitor C_f. For example, one end of the high switch SH 1  is connected to a positive terminal of the rechargeable battery cell C 1  and the other end of the high switch SH 1  is connected to the other end of the second capacitor C_f. One end of the high switch SH 16  is connected to a positive terminal of the rechargeable battery cell C 16  and the other end of the high switch SH 16  is connected to the other end of the second capacitor C_f. In this way, the high switches SH 1  to SH  16  are respectively connected to the positive terminals of the rechargeable battery cells C 1  to C 16  connected in series. 
     One end of the first capacitor C_V is connected to the negative terminal V− of the rechargeable battery cell unit  12  while the other end of the first capacitor C_V is connected to a positive terminal of the rechargeable battery cell C 2  via the first switch SW 1 . The other end of the second capacitor C_f is connected to the other end of the first capacitor C_V via the second switch SW 2 . The other end of the first capacitor C_V is connected to the low-voltage circuit, and the first capacitor C_V supplies a power supply voltage VDD to the low-voltage circuit. 
     One end of the second capacitor C_f is connected ends on the other side of the low switches SL 0  to SL 15 . The other end of the second capacitor C_f is connected to ends on the other side of high switches SH 1  to SH  16  and the other end of the first capacitor C_V via the second switch SW 2 . The second capacitor C_f operates as a charge pump that charges the first capacitor C_V. 
     The power monitor  101  operates as a controller that controls the cell selector  102 , the first switch SW 1 , and the second switch SW 2  on the basis of a value of a power supply voltage VDD and a clock signal of the logic circuit  113 . The cell selector  102 , the first switch SW 1 , and the second switch SW 2  are also collectively referred to as a switch group. The power monitor  101  controls the charging and discharging of the first capacitor C_V and the second capacitor C_f by controlling the switch group. 
     Next, the power supply apparatus  100  will be explained with reference to  FIG. 4 . This figure is a timing chart showing the operation of the switch group and charge states of the first capacitor C_V and the second capacitor C_f. 
     (Charging Operation During Activation) 
     For example, when the charging apparatus  1  is connected to an external power source such as an electrical outlet or an external apparatus such as a personal computer (PC), which are not shown in figures, and starts charging or discharging operation, and the charge monitor  110  starts monitoring a charge state of the rechargeable battery cell unit  12 , then the power monitor  101  first controls the switch group so that the first capacitor C_V is charged to a predetermined voltage. Specifically, as shown in  FIG. 4 , the power monitor  101  controls the switch group so that the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  are turned on at the timing of time t 1  while switches other than these switches are turned off. 
       FIGS. 5A and 5B  show a circuit diagram of the rechargeable battery module  10  at time t 1 . By turning on the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  while switches other than these switches are turned off, the first capacitor C_V and the second capacitor C_f, and the rechargeable battery cells C 1  and C 2  are connected in parallel as indicated by the dashed line in  FIG. 5A .  FIG. 5B  shows an equivalent circuit showing a connected state of the rechargeable battery module  10  in  FIG. 5A . The first capacitor C_V and the second capacitor C_f are charged from the rechargeable battery cells C 1  and C 2 . 
     In this way, when the charge monitor  110  starts monitoring a charge state of the rechargeable battery cell unit  12 , the power monitor  101  first charges the first capacitor C_V and the second capacitor C_f from a power circuit being a power supply having a voltage equal to or higher than a predetermined value. This is because when the charge monitor  110  is not monitoring a charge state, the first capacitor C_V and the second capacitor C_f are neither charged nor discharged, and hence the voltages of the first capacitor C_V and the second capacitor C_f may be lowered. 
     For this reason, when the charge monitor  110  starts monitoring a charge state of the rechargeable battery cell unit  12 , the first capacitor C_V and the second capacitor C_f are charged from the power circuit having a predetermined voltage Vs as shown in  FIG. 4 . In this way, the voltage of the first capacitor C_V can be raised to a predetermined power supply voltage in a short period of time as shown in  FIG. 4 . In this embodiment, the rechargeable battery cells C 1  and C 2  connected in series are used as the power circuit. Rechargeable battery cells in another configuration may be used as the power circuit. For example, three or more rechargeable battery cells connected in series may be used as the power circuit. When the charge monitor  110  starts monitoring a charge state of the rechargeable battery cell unit  12 , a charging operation, during which the first capacitor C_V is charged to a predetermined power supply voltage, is referred to as “charging operation during activation.” 
     The charging operation during activation will be explained in detail with reference to  FIG. 6 . The power monitor  101 , when starting monitoring a charge state of the rechargeable battery cell unit  12 , controls the switch group so that the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  are turned on while switches other than these switches are turned off (Step S 101 ). By this control, charging of the first capacitor C_V and the second capacitor C_f from the rechargeable battery cells C 1  and C 2  serving as the power circuit is started as shown in  FIGS. 5A and 5B . 
     When the charging of the first capacitor C_V and the second capacitor C_f is started, the voltage of the first capacitor C_V and the voltage of the second capacitor C_f are raised as shown in  FIG. 4 . The power monitor  101  monitors the voltage of the first capacitor C_V, more specifically, a power supply voltage VDD of the other end of the first capacitor C_V. The power monitor  101  determines whether or not the power supply voltage VDD of the first capacitor C_V is equal to or higher than a first voltage Vmin  1  (Step S 102  in  FIG. 6 ). In this embodiment, the first voltage Vmin  1  is set to 2.9 V, which is higher than a minimum operating voltage (2.7 V) of the low-voltage circuit. 
     When the power supply voltage VDD of the first capacitor C_V does not exceed the first voltage Vmin  1  (No in Step S 102 ), the power monitor  101  returns to Step S 101  to allow the first capacitor C_V to be continuously charged. Meanwhile, when the power supply voltage VDD of the first capacitor C_V is equal to or higher than the first voltage Vmin  1  (Yes in Step S 102 ), the power monitor  101  turns off the first switch SW 1  and terminates the charging operation during activation (Step S 103 ). 
     (Normal Charging Operation) 
     Explanation returns to  FIG. 4 . As shown in this figure, when the power supply voltage VDD of the first capacitor C_V and the power supply voltage VDD of the second capacitor C_f reach the first voltage Vmin  1 , the power monitor  101  shifts operation from the activation charging operation to the normal charging operation. During the normal charging operation, the power monitor  101  performs normal charging processing, upper limit monitoring processing, and lower limit monitoring processing. 
     (Normal Charging Processing) 
     The normal charging processing will be explained in detail. In this processing, the second capacitor C_f performs charge pump operation on the basis of a clock signal generated by the logic circuit  113 . The clock signal is generated only after a power supply voltage is supplied to the logic circuit  113 . For this reason, as shown in  FIG. 4 , the clock signal is not generated from time t 1  to time t 2 . The clock signal is generated after time t 2  when the logic circuit  113  has been supplied with a power supply voltage VDD equal to or higher than a minimum operating voltage and started operating. 
     The power monitor  101  first controls the switch group so that the second capacitor C_f is charged from a predetermined rechargeable battery cell during a period when the clock signal is low (first period) (first control). Specifically, the power monitor  101  controls the switch group so that the second capacitor C_f is connected to a rechargeable battery cell having a highest voltage among the plurality of rechargeable battery cells C 1  to C 16  at the fall time of the clock signal. Here, the rechargeable battery cell C 3  is used as the rechargeable battery cell having the highest voltage. 
     The power monitor  101  controls the switch group so that the low switch SL 2  and the high switch SH 3  are turned on while switches other than these switches are turned off at the fall time of the clock signal (time t 2 ). By this control, as shown in  FIG. 7A , one end of the second capacitor C_f is connected to the negative terminal of the rechargeable battery cell C 3  while the other end of the second capacitor C_f is connected to the positive terminal of the rechargeable battery cell C 3 .  FIG. 7B  shows an equivalent circuit showing a connected state of the rechargeable battery module  10  in  FIG. 7A . In this way, with the second capacitor C_f and the rechargeable battery cell C 3  being connected to each other, the second capacitor C_f is charged such that the electric potential of the second capacitor C_f corresponds to the electric potential of the rechargeable battery cell C 3 . 
     Explanation returns to  FIG. 4 . Next, the power monitor  101  controls the switch group so that the first capacitor C_V is charged from the second capacitor C_f during a period when the clock signal is high (second period)(second control). Specifically, the power monitor  101  controls the switch group so that that the first capacitor C_V and the second capacitor C_f are connected to each other at the rise time of the clock signal. 
     The power monitor  101  controls the switch group so that the second switch SW 2  and the low switch SL 0  are turned on while switches other than these switches are turned off at the rise time of the clock signal (time t 3 ). By this control, as shown in  FIG. 8A , one end of the first capacitor C_V is connected to one end of the second capacitor C_f while the other end of the first capacitor C_V is connected to the other end of the second capacitor C_f.  FIG. 8B  shows an equivalent circuit showing a connected state of the rechargeable battery module  10  in  FIG. 8A . In this way, with the first capacitor C_V and the second capacitor C_f being connected to each other, the first capacitor C_V is charged from the second capacitor C_f such that the electric potential of the first capacitor C_V corresponds to the electric potential of the second capacitor C_f. 
     Then, the power monitor  101  controls the switch group so that the second capacitor C_f and a rechargeable cell having a maximum voltage are connected to each other in the subsequent first period. In this way, the power monitor  101  controls the switch group so that the first period, during which the second capacitor C_f and the rechargeable cell having the maximum voltage are connected to each other, and the second period, during which the first capacitor C_V and the second capacitor C_f are connected to each other, are repeated. By this control, the second capacitor C_f operates as a charge pump and the first capacitor C_V is charged to have a voltage within a predetermined voltage range by the second capacitor C_f. 
     In the above-mentioned normal charging processing, the first period is set as the period when the clock signal is low while the second period is set as the period when the clock signal is high. However, by setting each of the first period and the second period to be one cycle (high clock period and low clock period) of the clock signal, the first control and the second control may be repeated for every one cycle. The length of the first period of the first control and the length of the second period of the second control are determined on the basis of on-resistance of the switch group and a capacity value of the second capacitor C_f. The on-resistance of the switch group and the capacity value of the second capacitor C_f are determined such that a power supply voltage value or the like necessary for the charge monitor  110  is satisfied. In this embodiment, the charge monitor  101  selects a rechargeable cell having a maximum voltage on the basis of a notice from the logic circuit  113 . If the charge monitor  101  is not able to select the rechargeable cell having the maximum voltage when, for example, operation has shifted from the activation charging operation to the normal charging operation, a predetermined rechargeable cell may be selected. 
     (Upper Limit Monitoring Processing) 
     The upper limit monitoring processing executed by the power monitor  101  will be explained with reference to  FIG. 9 . This upper limit monitoring processing is executed to monitor whether or not the power supply voltage VDD of the first capacitor C_V exceeds a predetermined value when the power monitor  101  is performing the normal charging processing. 
     When performing the normal charging processing, the power monitor  101  monitors the power supply voltage VDD of the first capacitor C_V and determines whether or not the power supply voltage VDD is equal to or lower than a third voltage Vmax  1  (Step S 201 ). In this embodiment, the third voltage Vmax  1  is set to 3.5 V, which is lower than a maximum operating voltage (3.6 V) of the low-voltage circuit. 
     When the power supply voltage VDD is lower than the third voltage Vmax  1  (No in Step S 201 ), the power monitor  101  continues monitoring the power supply voltage VDD and normal charging processing. When the power supply voltage VDD is equal to or higher than the third voltage Vmax  1  (Yes in Step S 201 ), the power monitor  101  interrupts the normal charging processing and controls the switch group so that all the switches are turned off (Step S 202 ). 
     When the power monitor  101  turns off all the switches, the first capacitor C_V supplies a low power supply voltage and the first capacitor C_V is not charged from the second capacitor C_f. Therefore, the power supply voltage VDD of the first capacitor C_V is lowered. 
     The power monitor  101  monitors the power supply voltage VDD also after all the switches are turned off and determines whether or not the power supply voltage VDD is equal to or lower than a fourth voltage Vmax  2  (Step S 203 ). When the power supply voltage VDD is higher than the fourth voltage Vmax  2  (No in Step S 203 ), the power supply monitor  101  continues monitoring the power supply voltage VDD, with all the switches being turned off. Meanwhile, when the power supply voltage VDD is equal to or lower than the fourth voltage Vmax  2  (Yes in Step S 203 ), the power monitor  101  restarts the interrupted normal charging processing and returns to Step S 201  to continue monitoring the power supply voltage VDD. In this embodiment, the fourth voltage Vmax  2  is 3.4 V, which is lower than the third voltage Vmax  1 . 
     (Lower Limit Monitoring Processing) 
     The lower limit processing executed by the power monitor  101  will be explained with reference to  FIG. 10 . This lower limit monitoring processing is executed to monitor whether or not the power supply voltage VDD of the first capacitor C_V is below a predetermined value when the power monitor is performing the normal charging processing. 
     When performing the normal charging processing, the power monitor  101  monitors the power supply voltage VDD of the first capacitor C_V and determines whether the power supply voltage VDD is equal to or lower than a second voltage Vmin  2  (Step S 301 ). In this embodiment, the second voltage Vmin  2  is set to 2.8 V, which is higher than the minimum operating voltage (2.7 V) of the low-voltage circuit. 
     When the power supply voltage VDD is higher than the second voltage Vmin  2  (No in Step S 301 ), the power monitor  101  continues monitoring the power supply voltage VDD and the normal charging processing. When the power supply voltage VDD is equal to or lower than the second voltage Vmin  2  (Yes in Step S 301 ), the power monitor  101  interrupts the normal charging processing and controls the switch group so that the first capacitor C_V is charged from the power circuit (the rechargeable cells C 1  and C 2  in this embodiment), which is a stable power supply. Specifically, the power monitor  101  controls the switch group so that the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  are turned on while switches other than these switches are turned off (Step S 302 ). By this control, the rechargeable battery module  10  is held in the connected state as shown in  FIGS. 5A and 5B , and the first capacitor C_V and the second capacitor C_f are charged from the rechargeable battery cells C 1  and C 2 , which serve as the power circuit. Hence, the power supply voltage VDD of the first capacitor C_V and the power supply voltage VDD of the second capacitor C_f are raised. 
     The power monitor  101  monitors the power supply voltage VDD also after the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  are turned on. The power monitor  101  determines whether or not the power supply voltage VDD is equal to or higher than the first voltage Vmin  1  (Step S 303 ). When the power supply voltage VDD is lower than the first voltage Vmin  1  (No in Step S 303 ), the power monitor  101  continues monitoring the power supply voltage VDD, with the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  being turned on. Meanwhile, when the power supply voltage VDD is equal to or higher than the first voltage vmin  1  (Yes in Step S 303 ), the power monitor  101  restarts the interrupted normal charging processing and returns to Step S 301  to continue monitoring the power supply voltage VDD. Here, the first voltage Vmin  1  is higher than the second voltage Vmin  2 . In this embodiment, as discussed above, the first voltage Vmin  1  is set to 2.9 V. 
     As thus explained, by the power monitor  101  executing the upper limit monitoring processing and the lower limit monitoring processing while performing the normal charging processing, it is possible to keep the power supply voltage VDD of the first capacitor C_V within an appropriate voltage range within which the low-voltage circuit can be operated. In order to determine whether or not the power supply voltage VDD is within the appropriate voltage range, two thresholds are used for each of the upper and lower limits, providing hysteresis for determination. This can prevent the power supply voltage VDD from becoming unstable and departing from the appropriate voltage range when a charge target of the first capacitor C_V is switched to another charge target. 
     Next, a configuration example of the power monitor  101  will be explained with reference to  FIG. 11 . The power monitor  101  has a reference voltage generating unit  121 , first and second comparators  122  and  123 , and a control signal generating unit  124 . 
     The reference voltage generating unit  121  generates a reference voltage to be used by the power monitor  101  for determination in the activation charging operation, the upper limit monitoring operation, and the lower limit monitoring operation. As described below, since the first and second comparators  122  and  123  have hysteresis, the reference voltage is determined taking into account the hysteresis. 
     The first comparator  122  is a circuit for determining whether or not the power supply voltage VDD is equal to or higher than the third voltage Vmax  1  and whether or not the power supply voltage VDD is equal to or lower than the fourth voltage Vmax  2 . To the first comparator  122 , the power supply voltage VDD and the reference voltage generated by the reference voltage generating unit  121  are input. The first comparator  122  outputs a high signal when the power supply voltage VDD is equal to or higher than the third voltage Vmax  1 . The first comparator  122  outputs a low signal when the power supply voltage VDD is equal to or lower than the fourth voltage Vmax  2 . In this way, the first comparator  122  has hysteresis. 
     The second comparator  123  is a circuit for determining whether or not the power supply voltage VDD is equal to or higher than the first voltage Vmin  1  and whether or not the power supply voltage VDD is equal to or lower than the second voltage Vmin  2 . To the second comparator  123 , the power supply voltage VDD and the reference voltage generated by the reference voltage generating unit  121  are input. The second comparator  123  outputs a high signal when the power supply voltage VDD is equal to or higher than the first voltage Vmin  1 . The second comparator  123  outputs a low signal when the power supply voltage VDD is equal to or lower than the second voltage Vmin  2 . In this way, the second comparator  123  has hysteresis. 
     The control signal generating unit  124  generates a control signal for controlling the switch group on the basis of the outputs of the first and second comparators  122  and  123 , and a clock signal obtained from the logic circuit  113 . 
     The control signal generating unit  124  starts the activation charging operation, upon receiving, for example, from the charge monitoring controller  3  an instruction to start monitoring a rechargeable battery cell. Starting the activation charging operation, the control signal generating unit  124  first generates a control signal for turning on the first and second switches SW 1  and SW 2  and the low switch SL 0  while turning off switches other than these switches. With this signal, the first capacitor C_V and the second capacitor C_f are charged. 
     Upon the reception of the high signal input from the second comparator  123  during the activation charging operation, the control signal generating unit  124  determines that the power supply voltage VDD is equal to or higher than the first voltage Vmin  1 , and controls the switch group so that the activation charging operation is terminated and then operation is shifted to the normal charging operation. Specifically, as shown in  FIG. 4 , a control signal for turning on the low switch SL 2  and the high switch SH 3  while turning off switches other than these switches is generated. After generating this signal, the control signal generating unit  124  alternately generates, on the basis of a clock signal, a control signal for turning on the second switch SW 2  and the low switch SL 0  while tuning off switches other than these switches and a control signal for turning on the low switch SL 2  and the high switch SH 3  while turning off switches other than these switches. 
     Upon the reception of the high signal input from the first comparator  122  during the normal charging processing, the control signal generating unit  124  determines that the power supply voltage VDD is equal to or higher than the third voltage Vmax  1 , and generates a control signal for turning off all the switches. When the output of the first comparator  122  changes from the high signal to the low signal, the control signal generating unit  124  determines that the power supply voltage VDD is equal to or lower than the fourth voltage Vmax  2 , and returns to the normal charging processing. 
     Upon the reception of the low signal input from the second comparator  123  during the normal charging processing, the control signal generating unit  124  determines that the power supply voltage VDD is equal to or lower than the second voltage Vmin  2 , and generates a control signal for turning on the first switch SW 1 , the second switch SW 2 , and the low switch SL 0  while turning off switches other than these switches. When the output of the second comparator  123  changes from the low signal to the high signal, the control signal generating unit  124  determines that the power supply voltage VDD is equal to or higher than the first voltage Vmin  1 , and returns to the normal charging processing. 
     As thus explained, the power supply apparatus  100  in the first embodiment uses the second capacitor C_f as the charge pump and charges the first capacitor C_V from the rechargeable battery cell having the maximum voltage. By this charging, a power supply voltage can be supplied to a low-voltage circuit without using a step-down circuit. Therefore, the power supply apparatus  100  can supply a power voltage to a monitoring circuit with low power consumption because power consumption for stepping down voltage is suppressed. 
     Although not illustrated in figures, each component of the power monitor  101  shown in  FIG. 11  receives a power voltage supply from the rechargeable battery cell unit  12 , with a first power supply electric potential and a second power supply electric potential being connected to a positive terminal V+ and a negative terminal V− of the rechargeable battery cell unit  12 . Each of these components of the power monitor  101  can be formed to have a configuration in which a large electric current is not necessary and only minimum electric current of appropriately from several μAs to a few tens of μAs, for example, is necessary. Therefore, a configuration that has almost no impact on the power consumption of the power supply apparatus  100  can be realized. 
     By charging the second capacitor C_f from the rechargeable battery cell having the maximum voltage, the voltage of the rechargeable battery cell having the maximum voltage is lowered. Thus, cell balancing of the plurality of rechargeable battery cells and charging the second capacitor C_f can be both achieved. 
     In this embodiment, the cell selector  102  and the measurement cell selector  111  are provided separately. However, the measurement cell selector  111  may be omitted by setting the charge monitor  110  and the power supply apparatus  100  to share the cell selector  102 . 
     (Modification 1) 
     Next, a modification of the first embodiment will be explained. In this modification, processing to be implemented when a power supply voltage VDD exceeds an upper limit in upper limit monitoring processing is different from that in the first embodiment. 
     Upper limit monitoring processing according to this modification will be explained with reference to  FIG. 12 . As in the first embodiment, the power monitor  101  determines whether or not the power supply voltage VDD is equal to or higher than the third voltage Vmax  1  in Step S 201 . 
     When the power supply voltage VDD is equal to or higher than the third voltage Vmax  1  (Yes in Step S 201 ), the power monitor  101  interrupts the normal charging processing and controls the switch group so that the second capacitor C_f and a rechargeable cell having a lowest voltage are connected to each other (Step S 204 ). Here, the explanation is given on the assumption that the rechargeable battery cell C 16  is used as the rechargeable battery cell having the lowest voltage. 
     When the power supply voltage VDD is equal to or higher than the third voltage Vmax  1 , the power monitor  101  interrupts the normal charging processing and controls the switch group so that the high switch SH 16  and the low switch SL 15  are turned on while switches other than these switches are turned off. By this control, as shown in  FIG. 13 , the second capacitor C_f and the rechargeable battery cell C 16  having the minimum voltage are connected to each other and the rechargeable battery cell C 16  is charged by the second capacitor C_f. With the second capacitor C_f and the rechargeable battery cell C 16  being connected to each other, the first capacitor C_V is not charged from the second capacitor C_f such that the power supply voltage VDD of the first capacitor C_V is lowered. 
     The power monitor  101  monitors the power supply voltage VDD also after the connection between the second capacitor C_f and the rechargeable battery cell C 16  having the minimum voltage is established, and determines whether or not the power supply voltage VDD is equal to or higher than the fourth voltage Vmax  2  (Step S 203 ). Processing subsequent to this operation is similar to the upper limit monitoring processing explained with reference to  FIG. 9 . 
     As thus explained, in this modification, by charging the rechargeable battery cell having the minimum voltage from the second capacitor C_f, cell balancing of the rechargeable battery cells to keep a predetermined voltage can be performed. 
     In this modification, the second capacitor C_f charges only the rechargeable battery cell C 16 . However, when a charge target is changed from the rechargeable battery cell C 16  having the minimum voltage to another rechargeable battery cell, the power monitor  101  may switch a connection target of the second capacitor C_f from the rechargeable battery cell C 16  to another rechargeable battery cell. The logic circuit  113  gives a notice of the rechargeable cell having the maximum voltage. 
     In this modification, when the power supply voltage VDD is equal to or higher than the third voltage Vmax  1  during the upper limit monitoring processing, the rechargeable cell having the minimum voltage is charged. Alternatively, charging of the rechargeable cell having the minimum voltage may be simultaneously performed when the first capacitor C_V is being charged from the second capacitor C_f. Alternatively, a cell balancing operation period may be established, in which the normal charging operation is interrupted and the rechargeable battery cell having the minimum voltage is charged from the second capacitor C_f for a predetermined period of time. 
     Second Embodiment 
     A rechargeable battery module  20  according to a second embodiment will be explained with reference to  FIGS. 14A and 14B . The rechargeable battery module  20  according to this embodiment differs from the first embodiment in that the second capacitor C_f is charged from a rechargeable battery cell having a maximum voltage and a rechargeable battery cell connected in series to this rechargeable battery cell having the maximum voltage. Except for this difference, the rechargeable battery module  20  in the second embodiment has the same as that of the rechargeable battery module  10  in the first embodiment, and the rechargeable battery module  20  is installed to the charging apparatus  1 . 
     A power monitor  201  according to this embodiment controls the switch group so that the second capacitor C_f is charged from a predetermined rechargeable battery cell during a period when a clock signal is low (first period) during the normal charging processing (first control). In this embodiment, the power monitor  201  selects as a predetermined rechargeable battery cell a rechargeable battery cell having a maximum voltage and a rechargeable battery cell connected in series to this rechargeable battery cell having the maximum voltage. Here, the explanation is given on the assumption that the rechargeable battery cell C 3  is used as the rechargeable battery cell having the maximum voltage and the power monitor  201  selects the rechargeable battery cell C 3  and the rechargeable battery cell C 2  connected in series to the rechargeable battery cell C 3 . 
     The power monitor  201  controls the switch group so that the low switch SL 1  and the high switch SH 3  are turned on while switches other than these switches are turned off at the fall time of the clock signal during the normal charging processing. By this control, as shown  FIG. 14A , one end of the second capacitor C_f is connected to a negative terminal of the rechargeable battery cell C 2  while the other end of the second capacitor C_f is connected to a positive terminal of the rechargeable battery cell C 3 .  FIG. 14B  shows an equivalent circuit showing a connected state of the rechargeable battery module  20  in  FIG. 14A . In this way, by connecting the second capacitor C_f to the rechargeable battery cells C 2  and C 3 , the second capacitor C_f is charged from the rechargeable battery cells C 2  and C 3 . Other than this operation, operations in the second embodiment are the same as those in the first embodiment. 
     As thus explained, the rechargeable battery module  20  according to the second embodiment is able to yield effects similar to those in the first embodiment, and moreover the second capacitor C_f in the second embodiment can be charged to a higher voltage as compared to the first embodiment since a plurality of rechargeable battery cells are used to charge the second capacitor C_f in the second embodiment. Therefore, this embodiment is useful when a higher power supply voltage VDD is to be supplied to a low-voltage circuit, as represented by a case where consumption current of the ADC  112  or the logic circuit  113  is high or a case where the power supply voltage VDD is also supplied to a low-voltage circuit in addition to the ADC  112  and the logic circuit  113 . 
     In the above-mentioned embodiment, the second capacitor C_f is charged from two rechargeable battery cells, but the second capacitor C_f may be charged by three or more rechargeable battery cells connected in series. 
     Third Embodiment 
     Next, a rechargeable battery cell  30  according to a third embodiment will be explained with reference to  FIG. 15 . The rechargeable battery cell  30  according to this embodiment has a third capacitor C_f  2  and third to fifth switches SW 3  to SW 5 . Other than this configuration, the rechargeable battery module  30  in the third embodiment has the same configuration as that of the rechargeable battery module  10  in the first embodiment, and the rechargeable battery module  30  is installed to the charging apparatus  1 . 
     One end of the third capacitor C_f  2  is connected to ends on the other side of the low switches SL 0  to SL 15  while the other end of the third capacitor C_f  2  is connected to ends on the other side of the high switches SH 1  to SH 16  via the fourth switch SW 4 . The other end of the third capacitor C_f  2  is connected to one end of the second capacitor C_f via the fifth switch SW 5 . The third capacitor C_f  2  operates as a charge pump that charges the first capacitor C_V. 
     One end of the third switch SW 3  is connected to the second capacitor C_f while the other end of the third switch SW 3  is connected to ends on the other side of the low switches SL 0  to SL 15 . 
     A power monitor  301  operates as a controller that controls the cell selector  102  and the first to fifth switches SW 1  to SW 5  on the basis of a value of a power supply voltage VDD or a clock signal of the logic circuit  113 . The cell selector  102  and the first to fifth switches SW 1  to SW 5  are also collectively referred to as a switch group. The power monitor  301  controls the switch group to control the charging and discharging of the first to third capacitors C_V, C_f, and C_f  2 . 
     Next, operation of the rechargeable battery module  30  will be explained. First, the charging operation during activation will be explained with reference to  FIGS. 16A and 16B . 
     (Charging Operation During Activation) 
     The power monitor  301  controls the switch group so that the low switch SL 0  and the first to fourth switches SW 1  to SW 4  are turned on while switches other than these switches are turned off. By this control, the first to third capacitors C_V, C_f, and C_f  2  and the rechargeable battery cells C 1  and C 2  connected in series are connected in parallel as indicated by the dashed line in  FIG. 16A .  FIG. 16B  shows an equivalent circuit showing a connected state of the rechargeable battery module  30  in  FIG. 16A . The first to third capacitors C_V, C_f, and C_f  2  are charged from the rechargeable battery cells C 1  and C 2 . Operations other than this operation are the same as those in the first embodiment. 
     (Normal Charging Operation) 
     When the power supply voltage VDD of the first capacitor C_V reaches the first voltage Vmin  1 , the power monitor  301  shifts operation from the charging operation during activation to the normal charging operation. During the normal charging operation, the power monitor  301  performs normal charging processing, upper limit monitoring processing, and lower limit monitoring processing as in the power monitor in the first embodiment. 
     (Normal Charging Operation) 
     In the normal charging operation, the second capacitor C_f and the third capacitor C_f  2  perform charge pump operation on the basis of a clock signal generated by the logic circuit  113 . The power monitor  301  connects the second capacitor C_f and the third capacitor C_f  2  in parallel to be charged from the rechargeable battery cell C 3  having a maximum voltage during a period when the clock signal is low (first period). Specifically, the power monitor  301  controls the switch group so that the low switch SL 2 , the high switch SH 3 , and the third and fourth switches SW 3  and SW 4  are turned on while switches other than these switches are turned off at the fall time of the clock signal. 
     By this control, as shown in  FIG. 17A , ends on one side of the second capacitor C_f and the third capacitor C_f  2  are connected to a negative terminal of the rechargeable battery cell C 3  and ends on the other side of the second capacitor C_f and the third capacitor C_f  2  are connected to the positive terminal of the rechargeable battery cell C 3 .  FIG. 17B  shows an equivalent circuit showing a connected state of the rechargeable battery module  30  in  FIG. 17A . In this way, by connecting the second and third capacitors C_f and C_f  2  to the rechargeable battery cell C 3  in parallel, the second and third capacitors C_f and C_f  2  are charged such that the electric potential of the second capacitor C_f and the electric potential of third capacitors C_f  2  correspond to the electric potential of the rechargeable battery cell C 3 . 
     Next, the power monitor  301  charges the first capacitor C_V by connecting the second capacitor C_f and the third capacitor C_f  2  to each other in series during a period when the clock signal is high (second period). Specifically, the power monitor  301  controls the switch group so that the low switch SL, the second switch SW 2 , and the fifth switch SW 5  are turned on while switches other than these switches are turned off at the rise time of the clock signal. 
     By this control, the second and third capacitors C_f and C_f  2  connected in series are connected to the first capacitor C_V in parallel as shown in  FIG. 18A .  FIG. 18B  shows an equivalent circuit showing a connected state of the rechargeable battery module  30  in  FIG. 18A . In this way, with the second and third capacitors C_f and C_f  2  being connected in series to each other, the first capacitor C_V is charged such that the electric potential of the first capacitor C_V corresponds to a combined electric potential of the second and third capacitors C_f and C_f  2 . Hence, the first capacitor C_V is charged such that the electric potential of the first capacitor C_V is about twice as high as the electric potential of the rechargeable battery cell C 3 . 
     As thus explained, by performing charge pump operation using the third capacitor C_f  2  in addition to the second capacitor C_f, the voltage of the rechargeable cell C 3  is approximately doubled before charging the first capacitor C_V. 
     In the above-mentioned embodiment, the use of two capacitors (the second capacitor C_f and the third capacitor C_f  2 ) to perform charge pump operation has been explained. However, the charge pump operation may be performed using three or more capacitors. 
     As thus explained, the rechargeable battery module  30  according to the third embodiment yields the same effects similar to those in the first embodiment. Moreover, due to the provision of the third capacitor C_f  2 , the voltage of the rechargeable cell C 3  is raised before charging the first capacitor C_V. This embodiment is useful when a greater power supply voltage VDD is to be supplied to a low-voltage circuit, as represented by a case where consumption current of the ADC  112  or the logic circuit  113  is high or a case where the power supply voltage VDD is also supplied to a low-voltage circuit in addition to the ADC  112  and the logic circuit  113 . 
     Fourth Embodiment 
     A rechargeable battery module  40  according to a fourth embodiment will be explained with reference to  FIG. 19 . The rechargeable battery module  40  according to this embodiment differs from the first embodiment in that a stabilized power supply unit  400  is used as a power supply circuit. Except for this difference, the rechargeable battery module  40  in the fourth embodiment has the same configuration as that of the rechargeable battery module  10  in the first embodiment, and the rechargeable battery module  40  is installed to the charging apparatus  1 . 
     The stabilized power supply unit  400  is constituted of, for example, a constant-voltage circuit. This stabilized power supply unit  400  is connected to the first capacitor C_V via the first switch SW 1  and charges the first capacitor C_V. 
     A power monitor  401  controls the switch group so that the first switch SW 1  is turned on while switches other than this first switch are turned off when it is determined that in the lower limit monitoring processing, the power supply voltage VDD is equal to or lower than the second voltage Vmin  2  and that charging has to be performed from the power supply circuit (Yes in Step S 301  in  FIG. 10 ) or when the charging operation during activation is executed. By this control, the first capacitor C_V is charged from the stabilized power supply unit  400  serving as the power supply circuit. 
     As thus explained, the rechargeable battery module  40  according to the fourth embodiment yields the same effects similar to those in the first embodiment, and by providing the stabilized power supply unit  400  serving as the power supply circuit, the first capacitor C_V can be charged more stably. 
     In this embodiment, adoption of the stabilized power supply unit  400  to the rechargeable battery module  10  according to the first embodiment has been explained, but the stabilized power supply unit  400  may also be adopted to the rechargeable battery module  20  according to the second embodiment or the rechargeable battery module  30  according to the third embodiment. 
     Fifth Embodiment 
     A rechargeable battery module  50  according to a fifth embodiment will be explained with reference to FIG.  20 . The rechargeable battery module  50  according to this embodiment differs from the first embodiment in that the rechargeable battery cell unit  12  and a stabilized power supply unit  500  are used as power supply circuits. Except for this difference, the rechargeable battery module  50  in the fifth embodiment has the same configuration as that of the rechargeable battery module  10  in the first embodiment, and the rechargeable battery module  50  is installed to the charging apparatus  1 . 
     The stabilized power supply unit  500  is constituted of, for example, a step-down circuit. This stabilized power supply unit  500  is connected to the first capacitor C_V via the first switch SW 1 . The stabilized power supply unit  500  steps down the voltage of the rechargeable battery cell unit  12  before charging the first capacitor C_V. 
     A power monitor  501  controls the switch group so that the first switch SW 1  is turned on while switches other than this first switch are turned off when it is determined that in the lower limit monitoring processing, the power supply voltage VDD is equal to or lower than the second voltage Vmin  2  and that charging has to be performed from the power supply circuit (Yes in Step S 301  in  FIG. 10 ) or when the charging operation during activation is executed. By this control, the first capacitor C_V is charged from the stabilized power supply unit  400  serving as the power supply circuit. 
     As thus explained, the rechargeable battery module  50  according to the fifth embodiment yields the same effects similar to those in the first embodiment, and by using the rechargeable battery cell unit  12  and the stabilized power supply unit  500  as the power supply circuits, the first capacitor C_V can be charged more stably. Since the period of charging by the stabilized power supply unit  500  is shorter than the period of charge pump operation by the second capacitor C_F, the power consumed by the stabilized power supply unit  500  exerts only a minor impact on overall power consumption of the rechargeable battery module  50 . 
     In this embodiment, adoption of the stabilized power supply unit  500  to the rechargeable battery module  10  according to the first embodiment has been explained, but the stabilized power supply unit  500  may also be adopted to the rechargeable battery module  20  according to the second embodiment or the rechargeable battery module  30  according to the third embodiment. 
     Sixth Embodiment 
     A rechargeable battery module  60  according to a sixth embodiment will be explained with reference to  FIG. 21 . The rechargeable battery module  60  according to this embodiment has a low drop out (LDO) circuit  600 . Other than this, the rechargeable battery module  60  in the sixth embodiment has the same configuration as that of the rechargeable battery module  10  in the first embodiment, and the rechargeable battery module  60  is installed to the charging apparatus  1 . 
     The LDO circuit  600 —a linear regulator with a low drop out voltage—is a circuit capable of outputting a predetermined voltage even if a difference between a voltage input to the LDO circuit  600  and a voltage output by the LDO circuit  600  is small. This LDO circuit  600  is capable of supplying a predetermined output voltage to a low-voltage circuit even when the power supply voltage VDD of the first capacitor C_V is lowered. 
     As thus explained, the rechargeable battery module  60  according to the sixth embodiment yields the same effects similar to those in the first embodiment. Due to the provision of the LDO circuit  600  between the first capacitor C_V and the low-voltage circuit, a stable power supply voltage VDD can be supplied to the low-voltage circuit. 
     In this embodiment, adoption of the LDO circuit  600  to the rechargeable battery module  10  according to the first embodiment has been explained, but the LDO circuit  600  may be adopted for the rechargeable battery modules  20  to  50  according to the second to fifth embodiments. 
     It should be noted that the above-mentioned embodiments are merely examples and the present disclosure is not limited to these embodiments. Hence, modifications can be made depending on the designs and the like without departing from the technical concept of the present disclosure. 
     The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2011-125801 filed in the Japan Patent Office on Jun. 3, 2011, the entire content of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.