Patent Publication Number: US-2015084581-A1

Title: Charging device configured to reduce power consumption during non-charging period

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2013-197022 filed Sep. 24, 2013. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a charging device, and particularly to a charging device suitable for charging secondary batteries used to power cordless power tools. 
     BACKGROUND 
     Battery packs that house secondary batteries have been widely used to supply power to various types of electrical equipment. However, there are some problematic issues in charging the secondary batteries contained in the battery packs. Various resolutions to these issues have been proposed. 
     For example, most charging devices of today are provided with a control unit that controls the charging voltage and charging current supplied to the secondary battery in order to charge the battery safely and efficiently. Since power is supplied from an external power supply to the control unit in this type of charging device even when the charging device is not charging a secondary battery, the charging device consumes external power even when the device is not charging a battery. 
     Japanese patent application publication No. 2011-78246 proposes a charging device capable of resolving this issue. This charging device is configured to consume little or no power from the external power supply once the secondary battery has become fully charged. 
     The conventional charging device described above attempts to reduce the consumption of external power by interrupting the supply of power from the external power supply to the control unit of the charging device when the secondary battery is fully charged and uses the charged secondary battery as a source for supplying power to the control unit. However, while this method reduces power consumption from the external power supply, the charging device does not provide a complete solution to the conventional issue because power is being consumed from the secondary battery, which is the target of the charging operation. 
     SUMMARY 
     In view of the foregoing, it is an object of the present invention to provide a charging device that reduces power consumption in both the external power supply and the secondary battery when the charging device is not charging the secondary battery. 
     In order to attain the above and other objects, the invention provides a charging device that may include a first connection portion, a charge controller, a power supply circuit, and a second connection portion. A secondary battery is connectable to the first connection portion. The charge controller is configured to control selected one of a charging voltage and a charging current, and apply the controlled charging voltage or the controlled charging current to the secondary battery through the first connection portion. The power supply circuit is configured to supply the charge controller with power for driving the charge controller. The second connection portion is connectable to an external power supply. For example supplying power from the power supply circuit to the charge controller may be halted to place the charge controller in a power cutoff state during a period of time from a time when the external power supply is connected to the second connection portion to a time when the secondary battery is connected to the first connection portion and also during a period of time from a time when the secondary battery has become fully charged to a time when the secondary battery is disconnected from the first connection portion. 
     According to another aspect, the present invention provides a charging device that may include a charge controller, and a power supply circuit. The charge controller is configured to control selected one of a charging voltage and a charging current, and apply the controlled charging voltage or the controlled charging current to a secondary battery. The power supply circuit is configured to supply the charge controller with power for driving the charge controller. For example, supplying power from the power supply circuit to the charge controller may be halted to place the charge controller in a power cutoff state except when the secondary battery is being charged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram for a charging device according to one embodiment of the present invention; and 
         FIGS. 2A and 2B  are flowcharts showing steps in a control process performed by the charging device according to the embodiment for charging a secondary battery. 
     
    
    
     DETAILED DESCRIPTION 
     A charging device  1  according to one embodiment of the present invention will be described while referring to  FIGS. 1 ,  2 A and  2 B.  FIG. 1  is a circuit diagram and block diagram showing the structure of a charging circuit  2  provided in the charging device  1  according to the embodiment. The charging circuit  2  includes a first rectifying and smoothing circuit  10 , a switching circuit  20 , a high-frequency transformer  30 , a switching power supply circuit  40 , a second rectifying and smoothing circuit  50 , a charging current/voltage control circuit  60 , a relay circuit  70 , a control unit  80 , a battery connection portion  90 , a release circuit  100 , a constant-voltage power supply circuit  110 , a cutoff holding circuit  120 , a battery voltage detection circuit  130 , a battery type detection circuit  140 , and a signal transmission circuit  150 . While the charging device  1  is connected to an AC power supply  200 , the charging device  1  can charge a battery pack (not shown) housing a secondary battery that is connected to the battery connection portion  90 . 
     The first rectifying and smoothing circuit  10  has an input portion  10 A that can be connected to the AC power supply  200 , and an output portion that is connected to the high-frequency transformer  30  through the switching circuit  20 . The input portion  10 A of the first rectifying and smoothing circuit  10  is an example of a second connection portion, and an example of an external power supply connection portion. The AC power supply  200  is an example of an external power supply. The first rectifying and smoothing circuit  10  is configured of a full-wave rectifying circuit  11  and a smoothing capacitor  12 . The first rectifying and smoothing circuit  10  rectifies and smooths voltage inputted from the AC power supply  200  and outputs the resulting voltage to the high-frequency transformer  30 . 
     The switching circuit  20  is configured of a PWM controller  22 , a MOSFET  21 , a capacitor  23 , and a signal transmission unit  24 . The PWM controller  22  is connected to the gate of the MOSFET  21  and performs what is known as pulse width modulation (PWM) control to control the output voltage to modify the drive pulse width of the MOSFET  21  based on a signal received from the signal transmission unit  24 . Through this PWM control, the switching circuit  20  controls the charging voltage and charging current and produces its own driving power source. 
     The MOSFET  21  has a source connected to the first rectifying and smoothing circuit  10  and a drain connected to a primary winding  31  of the high-frequency transformer  30 . The MOSFET  21  performs switching actions in response to a signal that the PWM controller  22  outputs to the gate of the MOSFET  21 . 
     The capacitor  23  stabilizes the voltage of the power supply inputted into the PWM controller  22 . The signal transmission unit  24  is a photocoupler or the like. 
     The high-frequency transformer  30  has the primary winding  31  mentioned above, and three windings provided on the secondary side. The three windings are a first secondary winding  32 , a second secondary winding  33 , and a third secondary winding  34 . The primary winding  31  is connected to the first rectifying and smoothing circuit  10  through the switching circuit  20  and induces voltage in the secondary windings under PWM control performed by the PWM controller  22 . 
     The switching power supply circuit  40  is configured of a rectifying diode  41 , a smoothing capacitor  42 , a diode  43 , a transistor  44 , a Zener diode  45 , and resistors  46  and  47 . The switching power supply circuit  40  is connected between the second secondary winding  33  of the high-frequency transformer  30  and the switching circuit  20  and supplies the power generated in the second secondary winding  33  to the switching circuit  20  for driving the PWM controller  22 . 
     Next, the configuration for driving the PWM controller  22  will be described. 
     When the AC power supply  200  is connected to the charging device  1 , the first rectifying and smoothing circuit  10  rectifies and smooths AC voltage supplied from the AC power supply  200 . The resultant voltage is applied to the PWM controller  22  through the resistor  46 , and current flows from the first rectifying and smoothing circuit  10  to ground via the resistor  46 , the diode  43 , the resistor  47  and Zener diode  45 . At this time, the PWM controller  22  starts up and begins to perform PWM control since the voltage applied to the PWM controller  22  is equal to or greater than the minimum operating voltage of the PWM controller  22 . When PWM control begins, a voltage is induced in the second secondary winding  33 . The induced voltage is rectified and smoothed by the rectifying diode  41  and smoothing capacitor  42  and applied to the collector of the transistor  44 . Further, current flows from the second secondary winding  33  to ground via the rectifying diode  41 , the resistor  47 , and Zener diode  45 , and a voltage at a node between the resistor  47  and Zener diode  45  is maintained at a prescribed value which corresponds to the breakdown voltage of the Zener diode  45 . At this time, current flows to the base of the transistor  44 , switching the transistor  44  to an ON state. Once the transistor  44  is in an ON state, the induced voltage of the second secondary winding  33  serves as the driving power source for continuously driving the PWM controller  22 . 
     The cutoff holding circuit  120  is configured of resistors  121 A,  121 B,  121 C,  121 D, and  121 E; transistors  122 A,  122 B, and  122 C; a Zener diode  123 ; and signal transmission units  124 A and  124 B. When the transistor  122 C is in an ON state, the cutoff holding circuit  120  interrupts the supply of power from the second secondary winding  33  to the PWM controller  22 , halting operations of the PWM controller  22  and placing the control power supply in a cutoff state. The control power supply is further maintained in the cutoff state by placing transistors  122 A and  122 B in an ON state. 
     The cathode of the Zener diode  123  is connected to the first rectifying and smoothing circuit  10  through the resistor  121 A, while the anode is connected to ground. When the voltage outputted from the AC power supply  200  and applied to the cathode of the Zener diode  123  through the first rectifying and smoothing circuit  10  and resistor  121 A is greater than the breakdown voltage of the Zener diode  123 , the voltage at the cathode of the Zener diode  123  is maintained at a prescribed voltage. 
     The transistor  122 A has an emitter connected to the first rectifying and smoothing circuit  10  through the resistor  121 A, a collector connected to ground through the resistor  121 D, and a base connected to the collector of the transistor  122 B through the resistor  121 B. The voltage regulated by the Zener diode  123  is applied to the emitter of the transistor  122 A. 
     The transistor  122 B has an emitter connected to ground, and a base connected to the collector of the transistor  122 A through the resistor  121 C. The transistor  122 C has a collector connected to a node between the Zener diode  45  and resistor  47  of the switching power supply circuit  40 , a base connected to the collector of the transistor  122 A through the resistor  121 A, and an emitter connected to ground. 
     The signal transmission unit  124 A is configured of a phototransistor. The latter has a collector connected to the emitter of the transistor  122 A and an emitter connected to the collector of the transistor  122 A. The signal transmission unit  124 A receives a cutoff signal for shutting down the PWM controller  22 . 
     One terminal of the signal transmission unit  124 B is connected to the base of the transistor  122 C through the resistor  121 E, and the other terminal is connected to ground. The signal transmission unit  124 B receives a release signal for releasing the cutoff state of the control power supply for the PWM controller  22 . 
     Next, the operations of the cutoff holding circuit  120  will be described. 
     When the charging device  1  is connected to the AC power supply  200 , i.e., the input portion  10 A of the first rectifying and smoothing circuit  10  is connected to the AC power supply  200 , voltage regulated by the Zener diode  123  is applied to the emitter of the transistor  122 A. However, none of the transistors in the cutoff holding circuit  120  turn on until the signal transmission unit  124 A receives a cutoff signal. At this time, the cutoff holding circuit  120  is in its initial state. 
     Upon receiving a cutoff signal, the signal transmission unit  124 A conducts electricity for a fixed period of time. Current flows to the base of the transistor  122 B through the resistor  121 C, switching the transistor  122 B to an ON state. At the same time, current flows to the base of the transistor  122 C through the resistor  121 E, switching the transistor  122 C to an ON state. By turning on the transistor  122 B, the base of the transistor  122 A is connected to ground through the resistor  121 B and the transistor  122 B, placing the transistor  122 A in an ON state. When the transistor  122 A is in an ON state, current flows to the respective bases of the transistors  122 B and  122 C, even after the signal transmission unit  124 A is no longer conductive. The transistors  122 A,  122 B, and  122 C are maintained in their ON states until the charging device  1  is disconnected from the AC power supply  200 , that is, the input portion  10 A of the first rectifying and smoothing circuit  10  is disconnected from the AC power supply  200  or the signal transmission unit  124 B receives the release signal. 
     By placing the transistor  122 C in an ON state, the node between the Zener diode  45  and resistor  47  of the switching power supply circuit  40  becomes connected to ground. Therefore, current no longer flows to the base of the transistor  44 , placing the transistor  44  in an OFF state, and the voltage induced in the second secondary winding  33  is no longer applied to the PWM controller  22 . Further, since the output from the AC power supply  200  is connected to ground through the resistor  46 , diode  43 , and resistor  47 , only voltage divided by the resistors  46  and  47  is applied to the PWM controller  22 . Since this divided voltage is lower than the minimum operating voltage of the PWM controller  22 , the PWM controller  22  cannot operate on this divided voltage alone. Hence, turning the transistor  122 C on and the transistor  44  off halts the operations of the PWM controller  22 . 
     Upon receiving the release signal, the signal transmission unit  124 B is rendered conductive for a fixed period of time. Consequently, the base of the transistor  122 C is connected to ground through the resistor  121 E. Similarly, the base of the transistor  122 B is connected to ground through the resistor  121 C. Since their bases are connected to ground, both transistors are turned off. When the transistor  122 B is turned off, the base of the transistor  122 A is disconnected from ground, placing the transistor  122 A in an OFF state. Hence, all transistors in the cutoff holding circuit  120  are returned to their initial OFF state when the signal transmission unit  124 B receives the release signal. Returning the cutoff holding circuit  120  to its initial state releases the control power supply from its cutoff state. Consequently, the transistor  44  of the switching power supply circuit  40  returns to its ON state, resuming driving the PWM controller  22 . 
     All of the transistors  122 A,  122 B, and  122 C are returned to an OFF state also when the charging device  1  is disconnected from the AC power supply  200 , returning the cutoff holding circuit  120  to its initial state. Operations for driving the PWM controller  22  resume once the charging device  1  is reconnected to the AC power supply  200 . 
     The second rectifying and smoothing circuit  50  is configured of a rectifying diode  51 , and a smoothing capacitor  52 . The second rectifying and smoothing circuit  50  rectifies and smooths power generated in the first secondary winding  32  of the high-frequency transformer  30  and outputs this power to the battery connection portion  90 . 
     The constant-voltage power supply circuit  110  is configured of a rectifying diode  111 , smoothing capacitors  112  and  113 , and a three-terminal regulator  114 . The constant-voltage power supply circuit  110  converts the power generated in the third secondary winding  34  to a desired voltage to produce a Vcc supply voltage for powering the control unit  80 , relay circuit  70 , detection units, and the like. The constant-voltage power supply circuit  110  is an example of a power supply circuit. 
     The charging current/voltage control circuit  60  is configured of a current/voltage negative feedback control circuit  61 , and a current detection resistor  62 . The charging current/voltage control circuit  60  detects the charging current using the current detection resistor  62 , compares this charging current to a reference value inputted from the control unit  80 , and outputs the difference to the switching circuit  20  through a signal transmission unit  63 . 
     The relay circuit  70  is configured of a relay  71 , a transistor  72 , and a resistor  73 . When a signal outputted from the control unit  80  flows to the base of the transistor  72  via the resistor  73 , the transistor  72  is turned on and current from the Vcc supply voltage flows to ground, turning the relay  71  on. When the relay  71  is in an ON state, power can be supplied to the secondary battery for charging the same. 
     A first connection portion or the battery connection portion  90  is configured of a positive terminal  90   a,  and a negative terminal  90   b.  The positive terminal  90   a  is connected to the second rectifying and smoothing circuit  50  via the relay  71 , and the negative terminal  90   b  is connected to the second rectifying and smoothing circuit  50  via the current detection resistor  62 . The battery connection portion  90  can be connected to a battery pack that accommodates a secondary battery, i.e., a secondary battery is connectable to the battery connection portion  90 . The charging device  1  can charge the secondary battery when the battery connection portion  90  is connected to the battery pack. 
     The release circuit  100  is configured of a capacitor  101 ; resistors  102 ,  103 , and  104 ; a transistor  105 ; and a signal transmission unit  106 . When the secondary battery is connected to the battery connection portion  90 , the release circuit  100  outputs a release signal to the cutoff holding circuit  120  holding the control power supply in the cutoff state in order to release the control power supply from the cutoff state. 
     The base of the transistor  105  is connected to the positive terminal  90   a  of the battery connection portion  90  through the capacitor  101  and resistor  102 . The collector of the transistor  105  is also connected to the positive terminal  90   a  through the resistor  104  and signal transmission unit  106 , while the emitter is connected to ground. 
     When a secondary battery is connected to the battery connection portion  90 , the positive terminal (not shown) of the secondary battery is connected to the capacitor  101  through the positive terminal  90   a.  Current flows from the positive terminal  90   a  to ground through the capacitor  101  and resistors  102  and  103  for only a fixed period of time during which charges are accumulated in the capacitor  101 , i.e., current flows to the resistor  102 . Thus, for this fixed period of time, current flows to the base of the transistor  105 , placing the transistor  105  in an ON state. When the transistor  105  is in an ON state, the signal transmission unit  106  becomes conductive, transmitting a release signal to the cutoff holding circuit  120 . Since the release circuit  100  is provided with a differentiating circuit configured of the capacitor  101  and resistor  102 , the release circuit  100  can minimize the power consumption of the secondary battery for outputting the release signal. 
     The battery voltage detection circuit  130  is configured of transistors  131  and  132 ; and resistors  133 ,  134 ,  135 , and  136 . The transistor  131  has a collector connected to the positive terminal  90   a  of the battery connection portion  90 , a base connected to the collector of the transistor  132  through the resistor  135 , and an emitter connected to ground through the resistors  133  and  134 . The base of the transistor  132  is connected to the Vcc supply voltage through the resistor  136 , and the emitter is connected to ground. 
     When the Vcc supply voltage is supplied, current flows to the base of the transistor  132 , switching the transistor  132  to an ON state. At this time, the base of the transistor  131  is connected to ground through the resistor  135 . When the base of the transistor  131  is connected to ground, the transistor  131  switches to an ON state. As a result, the terminal voltage of the secondary battery is divided by the resistors  133  and  134  and the resulting divided voltage value is outputted to the control unit  80 . 
     When the Vcc supply voltage is not supplied, the transistor  131  is no longer in an ON state. Accordingly, power from the secondary battery connected to the battery connection portion  90  is not consumed. 
     The battery type detection circuit  140  is provided for detecting a type of the secondary battery contained in the battery pack. The term “type” as used herein is intended to encompass materially distinguished battery, such as lithium-ion battery, and a number of battery cells contained in the battery pack. The battery pack contains a resistor having a specific resistance value identifying the type of the battery. The battery type detection circuit  140  is configured of a resistance value detection terminal  141 , and a fixed resistor  142 . When the battery pack is connected to the charging device  1 , the fixed resistor  142  and the battery type identifying resistor are connected in series, and a Vcc supply voltage is applied to the serially-connected resistors. The Vcc supply voltage is divided by the two resistors and a voltage developed across the battery type identifying resistor appears at the terminal  141  and is outputted to the control unit  80 . In this way, information about the type of the battery contained in the battery pack is given to the control unit  80 . 
     The control unit  80  is configured of a microcomputer. The microcomputer primarily has a control value switching function port  81 , a relay on/off port  82 , a battery voltage detection and full-charge determination port  83 , a battery detection and battery type determination port  84 , and a cutoff signal output port  85 . The control unit  80  is driven by a Vcc supply voltage supplied from the constant-voltage power supply circuit  110 . The control unit  80  can control selected one of a charging voltage and a charging current using the PWM controller  22  and apply the controlled charging voltage or the controlled charging current to the secondary battery through the battery connection portion  90 . The control unit  80  is an example of a charge controller. 
     The battery voltage detection and full-charge determination port  83  is connected to the battery voltage detection circuit  130  and receives a signal outputted by the battery voltage detection circuit  130 . 
     The battery detection and battery type determination port  84  is connected to the battery type detection circuit  140  and receives a signal outputted by the battery type detection circuit  140 . 
     The relay on/off port  82  is connected to the relay circuit  70 . Based on signals inputted into the battery voltage detection and full-charge determination port  83  and battery detection and battery type determination port  84 , the relay on/off port  82  outputs a signal to the relay circuit  70  for turning the relay circuit  70  on and off when starting and ending charging operations. 
     The control value switching function port  81  is connected to the charging current/voltage control circuit  60 . Based on signals inputted into the battery voltage detection and full-charge determination port  83  and battery detection and battery type determination port  84 , the control value switching function port  81  outputs a signal to the charging current/voltage control circuit  60  as a reference value. 
     The cutoff signal output port  85  is connected to the signal transmission circuit  150 . Under prescribed conditions, the cutoff signal output port  85  outputs a cutoff signal to the signal transmission circuit  150  for interrupting the driving power to the PWM controller  22 . 
     The signal transmission circuit  150  is configured of resistors  151  and  152 , a transistor  153 , and a signal transmission unit  154 . The collector of the transistor  153  is connected to a Vcc supply voltage through the resistor  151  and signal transmission unit  154 . The transistor  153  has a base connected to the cutoff signal output port  85  of the control unit  80  through the resistor  152 , and an emitter connected to ground. When a cutoff signal is outputted from the control unit  80 , the transistor  153  switches to an ON state, and the signal transmission unit  154  outputs a cutoff signal to the cutoff holding circuit  120 . 
     Next, steps in the process for controlling charging operations of the charging device  1  will be described with reference to the flowcharts in  FIGS. 2A and 2B . 
     In S 301  of  FIG. 2A , the charging device  1  is connected to the AC power supply  200  and AC power is inputted into the charging device  1 . After the charging device  1  has been connected to the AC power supply  200 , in S 302  the PWM controller  22  initiates PWM control, producing a voltage in each secondary winding of the high-frequency transformer  30 . In S 303  the constant-voltage power supply circuit  110  regulates the voltage generated in the third secondary winding  34  to output a constant voltage to the control unit  80 . As a result, the control unit  80  begins operating. 
     After the control unit  80  begins operating, in S 304  the control unit  80  determines whether a secondary battery is connected to the battery connection portion  90 . If the control unit  80  determines that a secondary battery is not connected, in S 306  the control unit  80  determines whether this non-connected state has been continuous for a prescribed period of time. The control unit  80  repeats the determinations in S 304  and S 306  while the non-connected state has not been continuous for the prescribed period of time. If the control unit  80  determines in S 306  that this non-connected state has continued for the prescribed period of time, in S 312  of  FIG. 2B  the control unit  80  outputs a cutoff signal to the signal transmission circuit  150 , and the signal transmission circuit  150  outputs a cutoff signal to the cutoff holding circuit  120  to halt operations of the PWM controller  22 . 
     However, if the control unit  80  determines in S 304  that a secondary battery is connected to the battery connection portion  90 , in S 305  the control unit  80  begins charging operations. Once charging has been initiated, in  5307  the control unit  80  determines whether the secondary battery has been disconnected. If the control unit  80  determines that the secondary battery has not been disconnected, in S 308  the control unit  80  determines whether a full-charge condition has been met. If the control unit  80  determines in S 308  that the full-charge condition has not been met, the control unit  80  returns to S 307  and again determines whether the secondary battery has been disconnected. The control unit  80  determines whether the secondary battery has been disconnected based on whether a signal has been inputted from the battery type detection circuit  140  into the battery detection and battery type determination port  84 . However, the control unit  80  may instead determine whether the secondary battery has been disconnected based on whether a signal has been inputted from the battery voltage detection circuit  130  into the battery voltage detection and full-charge determination port  83 . 
     When the control unit  80  determines in S 307  that the secondary battery has been disconnected or when the control unit  80  determines in S 308  that the full-charge condition has been met, in S 309  the control unit  80  outputs an OFF signal from the relay on/off port  82  to turn off the relay  71 . Turning off the relay  71  interrupts the supply of power to the secondary battery, halting the charging operation for the secondary battery. 
     After charging has been halted in S 309 , in S 310  the control unit  80  determines whether the battery was disconnected. If the control unit  80  determines that the secondary battery was disconnected, the control unit  80  returns to S 304  and again determines whether a secondary battery has been connected to the battery connection portion  90 . 
     However, if the control unit  80  determines in S 310  that the secondary battery has not been disconnected, in S 311  the control unit  80  determines whether a prescribed period of time has elapsed while the secondary battery has not been disconnected. If the control unit  80  determines in S 311  that the prescribed period of time has not elapsed while the secondary battery has not been disconnected, the control unit  80  returns to S 310  and again determines whether the secondary battery has been disconnected. 
     If the control unit  80  determines in S 311  that the prescribed period of time has elapsed while the secondary battery has not been disconnected, in S 312  the control unit  80  outputs a cutoff signal to the cutoff holding circuit  120  for halting operations of the PWM controller  22 . 
     Once the operations of the PWM controller  22  have been halted, in S 313  a voltage is no longer produced in all secondary windings, i.e., the first secondary winding  32 , second secondary winding  33 , and third secondary winding  34  of the high-frequency transformer  30 . At this time, the control unit  80 , detection units, and other components that require a Vcc supply voltage to operate are no longer driven and placed in power cutoff states because the Vcc supply voltage is not generated when voltage is not produced in the secondary windings of the high-frequency transformer  30 . 
     As described above, the control unit  80  halts operations of the PWM controller  22  in the switching circuit  20  in S 312  both when the prescribed period of time has elapsed while the secondary battery has not been connected (S 306 ) and when the prescribed period of time has elapsed while the secondary battery remains connected after charging ends because the full-charge condition was met (S 311 ). In other words, the control unit  80  halts the operations of the PWM controller  22  unless the secondary battery is being charged, and the control unit  80  is placed in the power cutoff state except when the secondary battery is being charged. 
     After power for driving the PWM controller  22  and the control unit  80  has been cut off, the charging device  1  is brought to a standby state. The state of the charging device  1  changes depending on whether a secondary battery has been connected to the battery connection portion  90  in S 314 . If a secondary battery remains connected to the battery connection portion  90  after charging has completed, in S 316  the cutoff holding circuit  120  continues to hold the control power supply in a cutoff state so that power for driving the control unit  80  remains suspended. However, if power for driving the PWM controller  22  and control unit  80  was cut off because a secondary battery was not connected to the battery connection portion  90  continuously for the prescribed period of time (i.e., if the process advanced to S 312  through S 306 ), in S 315  the release circuit  100  outputs a release signal to the cutoff holding circuit  120  when a secondary battery has been connected to the battery connection portion  90  in S 314 , releasing the control power supply from its cutoff state. After the cutoff state has been released, the process returns to S 302 . 
     Thus, the charging device  1  can reduce the amount of external power consumed while not performing charging operations by halting the operations of the PWM controller  22  and control unit  80 . The charging device  1  can begin charging the secondary battery immediately only by connecting the secondary battery to the battery connection portion  90 , because the release circuit  100  releases cutoff state of the control power supply held by the cutoff holding circuit  120  once the secondary battery is connected to the battery connection portion  90 . 
     Further, only a slight amount of power is consumed when the charging device  1  is in the standby state for supplying external power to the cutoff holding circuit  120  in order to hold the control power supply in a cutoff state. This configuration greatly reduces the amount of power consumption compared to a configuration in which external power is supplied to the control unit  80  for controlling the standby state (S 314 ). 
     In the charging device  1  mentioned above, supplying power from the constant-voltage power supply circuit  110  to the control unit  80  is halted to place the control unit  80  in the power cutoff state during a period of time from a time when the AC power supply  200  is connected to the input portion  10 A of the first rectifying and smoothing circuit  10  to a time when the secondary battery is connected to the battery connection portion  90  and also during a period of time from a time when the secondary battery has become fully charged to a time when the secondary battery is disconnected from the battery connection portion  90 . Hence, the charging device  1  can reduce the amount of power consumption before the start of charging and after the end of charging. 
     Further, the charging device  1  is provided with the release circuit  100  which acts on the control unit  80  to release from the power cutoff state and allows the constant-voltage power supply circuit  110  to supply the control unit  80  with power. In this way, releasing the control unit  80  from the power cutoff state is easily implemented with the provision of the release circuit  100 . 
     Further, since the release circuit  100  becomes operable in response to connection of the secondary battery to the battery connection portion  90 , the charging device  1  can begin charging the secondary battery automatically and immediately. 
     Further, since the control unit  80  is placed in the power cutoff state except when the secondary battery is being charged, the charging device  1  can suppress power consumption. 
     Further, the charging device  1  is provided with the cutoff holding circuit  120  configured to hold the power cutoff state until a prescribed condition is met. In other words, under the condition that the prescribed condition is not met, the Vcc supply voltage is not allowed to power the control unit  80 . As such the charging device  1  can reduce the amount of power consumption. 
     Further, since the release circuit  100  releases the control unit  80  from the power cutoff state and allows the constant-voltage power supply circuit  110  to supply the control unit  80  with power when the prescribed condition is met, the charging device  1  can immediately begin charging the secondary battery when the prescribed condition is met. In this embodiment, the prescribed condition refers to the secondary battery having been connected to the battery connection portion  90 . Therefore, when the prescribed condition is met, i.e., when the secondary battery is brought into connection to the charging device  1 , the latter can immediately begin charging the secondary battery. 
     Further since the release circuit  100  releases the control unit  80  from the power cutoff state and allows the constant-voltage power supply circuit  110  to supply the control unit  80  with power in response to connection of the secondary battery to the battery connection portion  90 , the control unit  80  is released from the power cutoff state automatically when the secondary battery is connected to the battery connection portion  90 . Accordingly the charging device  1  can begin charging the secondary battery automatically and immediately. 
     Further, the charging device  1  is provided with the input portion  10 A to which the AC power supply  200  is connectable, and the release circuit  100  releases the control unit  80  from the power cutoff state in response to disconnection of the AC power supply  200  from the input portion  10 A. Hence, releasing the control unit  80  from the power cutoff state can be implemented only by disconnecting the AC power supply from the input portion  10 A. 
     The release circuit  100  includes the differentiating circuit, and the release circuit  100  outputs the signal for releasing the control unit  80  from the power cutoff state. The signal is being outputted for the fixed period of time during which current flows to the differentiating circuit. As the signal is not outputted for an unlimited period of time, the charging device  1  can reduce the amount of power consumption. 
     Further, supplying power from the constant-voltage power supply circuit  110  to the control unit  80  starts from when the AC power supply  200  is connected to the input portion  10 A and ends when the prescribed period of time has elapsed under a condition that the secondary battery has been disconnected from the battery connection portion  90 . Hence, the charging device  1  can reduce the amount of power consumption after the secondary battery is disconnected from the battery connection portion  90 , that is, the charging device  1  can reduce the amount of power consumption during the charging device  1  is in the standby state.