Abstract:
A charging device includes a charging unit, a detecting unit, a determining unit, a current generating unit, an adjusting unit, and a display unit. The charging unit charges a battery. The detecting unit detects a voltage developed across the battery. The determining unit determines a charging state of the battery based on the voltage. The current generating unit generates a current. The adjusting unit adjusts the current based on the charging state. The display unit emits a first light having a first color and a first intensity in response to the current supplied thereto. The first intensity changes in accordance with changing of the current.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a charging device for charging a secondary battery such as a lithium ion secondary battery. 
         [0003]    2. Description of Related Art 
         [0004]    In general, a portable device uses a secondary battery that is chargeable with a charging device as a power supply. Japanese Patent Application Publication No. 10-174308 provides a charging device that displays a charged amount (remaining capacity) of the secondary battery with a plurality of LEDs each emitting a signal having a color corresponding to a charging state. 
       SUMMARY OF THE INVENTION 
       [0005]    However, since a worker who uses an electric tool often works at a place that is distant from the charging device, the distant worker cannot distinguish the signal emitted from the LED. Thus, the distant worker cannot distinguish the charging state, such as, a charging completed state. 
         [0006]    In view of the above-described drawbacks, it is an objective of the present invention to provide a charging device capable of informing a user who is distant from the charging device to some extent of the charging state clearly. 
         [0007]    In order to attain the above and other objects, the present invention provides a charging device including a charging unit, a detecting unit, a determining unit, a current generating unit, an adjusting unit, and a display unit. The charging unit charges a battery. The detecting unit detects a voltage developed across the battery. The determining unit determines a charging state of the battery based on the voltage. The current generating unit generates a current. The adjusting unit adjusts the current based on the charging state. The display unit emits a first light having a first color and a first intensity in response to the current supplied thereto. The first intensity changes in accordance with changing of the current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which: 
           [0009]      FIG. 1  shows a circuit diagram of a charging device of a preferred embodiment of the present invention; and 
           [0010]      FIG. 2  shows a flowchart illustrating a control of displaying charging states according to the charging device of the preferred embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]      FIG. 1  shows the circuit diagram of the charging device  1  according to the preferred embodiment of the present invention. The charging device  1  charges a battery pack  2  with power supplied from an alternating-current power supply P. 
         [0012]    The battery pack  2  includes a plurality of battery cells connected in series, a first battery type determination resistor  7  and a thermosensor  8 . The thermosensor  8  is a thermistor and provided close to the battery pack  2 . 
         [0013]    The charging device  1  is provided with a current detection unit  3 , a charging control signal transmission unit  4 , a charging current signal transmission unit  5 , a rectification smoothing circuit  6 , a second battery type determination resistor  9 , a rectification smoothing circuit  10 , a switching circuit  20 , a rectification smoothing circuit  30 , a power supply  40 , a microcomputer  50 , a charging current control circuit  60 , a charging current setting unit  70 , a battery temperature detection unit  80 , a battery voltage detection unit  90 , a charging voltage control unit  100 , and a display unit  120 . 
         [0014]    The rectification smoothing circuit  10  includes a full-wave rectifier circuit  11  and a smoothing capacitor  12 . The full-wave rectifier circuit  11  rectifies the alternating-current supplied from the alternating-current power supply P, and the smoothing capacitor  12  smoothes the direct-current outputted from the full-wave rectifier circuit  11 . 
         [0015]    The switching circuit  20  includes a high-frequency transformer  21 , a MOSFET  22 , and the PWM control IC  23 . The PWM control IC  23  changes the drive pulse width applied to the MOSFET  22  in order to adjust a voltage outputted to the rectification smoothing circuit  30 . 
         [0016]    The rectification smoothing circuit  30  includes a diode  31 , a smoothing capacitor  32 , and a discharging resistor  33 . The diode  31  rectifies the alternating-current supplied from the switching circuit  20 , and the smoothing capacitor  32  smoothes the direct-current outputted from the diode  31 . 
         [0017]    The second battery type determination resistor  9  divides a reference voltage Vcc together with the first battery determination resistor  7 . The divided voltage is outputted as cell number information indicative number of the cells included in the battery pack  2 . The charging current setting unit  70  includes resistors  71  and  72 . The reference voltage Vcc is divided by the resistors  71  and  72 , and the divided voltage is outputted as a reference value for setting the charging current. The battery temperature detection unit  80  includes resistors  81  and  82 . The reference voltage Vcc is divided by the thermosensor  8  and the resistors  81  and  82 , and the divided voltage is outputted as battery temperature information. The battery voltage detection unit  90  includes resistors  91  and  92 . The battery voltage is divided by the resistors  91  and  92 , and the divided voltage is outputted as battery voltage information. 
         [0018]    The current detection unit  3  is a resistor, and detects a voltage applied to the resistor in order to obtain a charging current flowing through the battery pack  2 . The charging current control circuit  60  includes operational amplifiers  61  and  65 , resistors  62 ,  63 ,  64 ,  66  and  67 , and a diode  68 , and outputs a current control signal based on both the charging current (the voltage) detected by the current detection unit  3  and the reference value outputted from the charging current setting unit  70 . 
         [0019]    The charging current signal transmission unit  5  is a photocoupler, and transmits the current control signal outputted from the charging current control circuit  69  to the PWM control IC  23 . 
         [0020]    The microcomputer  50  includes output ports  51   a  and  51   b , an A/D input port  52 , and a reset port  53 . The cell number information outputted from the second battery type determination resistor  9 , the battery temperature information outputted from the battery temperature detection unit  80 , the battery voltage information outputted from the battery voltage detection unit  90 , and the voltage detected by the current detection unit  3  are inputted into the A/D port  52 . 
         [0021]    The microcomputer  50  outputs a start signal, a stop signal, and a charging state signal from the output port  51   a . The charging state signal is the reference voltage Vcc. Further, the microcomputer  50  determinates the number of the cells included in the battery pack  2  based on the cell number information, and outputs a charging voltage control signal corresponding to the number of the cells from the output port  51   b . Note that the microcomputer  50  may determine a battery type based on the cell number information. 
         [0022]    The charging device  1  (the microcomputer  50 ) charges the battery back  2  at a constant current until the charging current reaches a predetermined current, and at a constant voltage after the charging current has reached the predetermined current. 
         [0023]    The charging voltage control unit  100  includes resistors  101 ,  104 ,  107 ,  108 ,  109 ,  110 ,  114 ,  115 ,  116 ,  117 ,  118 ,  119  and  120 , a potentiometer  103 , FETs  111 ,  112  and  113 , a capacitor  105 , a shunt regulator  106 , and a rectifier diode  102 . 
         [0024]    The shunt regulator  106  has a reference terminal, and controls a charging voltage based on a voltage inputted into the reference terminal. The resistors  107 ,  108 ,  109  and  110  are connected to the reference terminal of the shunt regulator  106  in parallel. The FETs  111 ,  112  and  113  are connected to the resistors  107 ,  108 ,  109  and  110  respectively. The charging voltage control signal outputted from the output port  51   b  is inputted into gate terminals of the FETs  111 ,  112  and  113 , causing the FETs  111 ,  112  and  113  to turn on. 
         [0025]    When the microcomputer  50  determines that the battery pack  2  has two cells, the microcomputer  50  does not output the charging voltage control signal from the output port  51   b  to any of the gate terminals of the FETs  111 ,  112  and  113 . Thus, a voltage divided by a series resistance of the resistor  101  and the potentiometer  103 , and the resistor  107  is inputted into the reference terminal to set a charging voltage corresponding to the two cells. 
         [0026]    When the microcomputer  50  determines that the battery pack  2  has three cells, the microcomputer  50  outputs the charging voltage control signal from the output port  51   b  to the gate terminal of the FET  111 . Thus, a voltage divided by the series resistance of the resistor  101  and the potentiometer  103 , and a parallel resistance of the resistor  107  and the resistor  108  is inputted into the reference terminal to set a charging voltage corresponding to the three cells. 
         [0027]    When the microcomputer  50  determines that the battery pack  2  has four cells, the microcomputer  50  outputs the charging voltage control signal from the output port  51   b  to the gate terminal of the FET  112 . Thus, a voltage divided by the series resistance of the resistor  101  and the potentiometer  103 , and a parallel resistance of the resistor  107  and the resistor  109  is inputted into the reference terminal to set a charging voltage corresponding to the four cells. 
         [0028]    When the microcomputer  50  determines that the battery pack  2  has five cells, the microcomputer  50  outputs the charging voltage control signal from the output port  51   b  to the gate terminal of the FET  113 . Thus, a voltage divided by the series resistance of the resistor  101  and the potentiometer  103 , and a parallel resistance of the resistor  107  and the resistor  110  is inputted into the reference terminal to set a charging voltage corresponding to the five cells. 
         [0029]    The charging control signal transmission unit  4  is a photocoupler, and transmits the start signal and the stop signal outputted from the output port  51   a  to the PWM control IC  23 . 
         [0030]    The power supply  40  includes transformers  41   a  to  41   c , a switching element  42 , a control element  43 , a rectifier diode  44 , capacitors  45  and  47 , a regulator  46 , and a reset IC  48 , and supplies power to the microcomputer  50  and the rectification smoothing circuit  6 . The rectification smoothing circuit  6  includes a transformer  6   a , a rectifier diode  6   b , and a smoothing capacitor  6   c , and supplies the power supplied from the power supply  40  to the PWM control IC  23 . 
         [0031]    The display unit  120  includes an LED  121 , resistors  122 ,  123 ,  124 ,  126 ,  127 ,  129  and  130 , an FET  125  of Pch, and a transistor  128 . The LED  121  includes a green diode G and a red diode R. When the charging state signal outputted from the output port  51   a  is inputted into the green diode G via the resistor  122 , the green diode G lights up with green color. When the charging state signal is inputted into the red diode R via the resistor  123 , the red diode R lights up with red color. 
         [0032]    The green diode is also connected to the reference voltage Vcc via the resistor  124  and the FET  125 . A gate of the FET  125  is connected to the output port  51   a  via the transistor  128 . When the charging state signal is inputted into the transistor  128 , the transistor  128  turns ON. When the transistor  128  turns ON, the FET  125  also turns ON. When the FET  125  turns ON, the reference voltage Vcc is applied to the green diode G via the resistor  124 , causing the green diode G to light up with the green color. 
         [0033]    Further, a resistance value of the resistor  124  is smaller than that of the resistor  122 . Thus, the green diode G lights up more strongly (blightly) when the current is flowed via the resistor  124  than when the current is flowed via the resistor  122 . 
         [0034]    Furthermore, when the charging state signal are inputted into both the green diode G via the resistor  122  and the red diode R via the resistor  123  concurrently, the LED  121  lights up with orange color. If a current is flowed through the LED  121  via the resistor  124 , green color surpasses red color. Accordingly, with respect to green color, a current is flowed via the resistor  122 . 
         [0035]    In the preferred embodiment, the LED  121  lights up with the red color before charging, with the orange color during charging, and with the green color after charging. 
         [0036]      FIG. 2  shows a flowchart illustrating a control of displaying the charging states. 
         [0037]    Before the battery pack  2  is attached to the charging device  1 , the microcomputer  50  outputs a high signal (the reference voltage Vcc) as the charging state signal from the output port  51   a  to the LED  121  via the resistor  123  so that the LED  121  lights up with the red color (step  201 ). 
         [0038]    Next, the microcomputer  50  determines whether or not the battery pack  2  is attached to the charging device  1  in response to the input from the battery temperature detection unit  80 , battery type determination unit  9 , and battery voltage detection unit  90  (step  202 ). If the battery pack  2  is attached (step  202 : YES), the microcomputer  50  determines the number of cells based on the cell number information inputted by the battery type determination unit  9  (step  203 ), and sets a charging voltage corresponding to the number of the cells determined in step  203  (step  204 ). 
         [0039]    Next, the microcomputer  50  outputs a low signal as the start signal from the output port  51   a  to the photocoupler  4  to set the PWM control IC  23  in an operation state (step  205 ). In this way, the charging is started. In the start of the charging, as is generally known, the microcomputer  50  charges the battery pack  2  at a constant current. The microcomputer  50  outputs high signals (the reference voltage Vcc) as the charging state signal from the output port  51   a  to the LED  121  via both the resistors  122  and  123  during charging so that the LED  121  lights up with the orange color (step  206 ). 
         [0040]    After the charging is started, the microcomputer  50  monitor the charging current based on the voltage inputted from the current detection unit  3  into the A/D port  52 . As the charging goes, the battery voltage increases gradually. When the battery voltage has reached a predetermined value, the microcomputer  50  changes the charging method from the constant current charging to the constant voltage charging. When the battery pack  2  is charged at the constant voltage, the charging current reduces gradually. 
         [0041]    The microcomputer  50  determines whether the charging current (the voltage) has reached a predetermined current (s 207 ). If the charging current has reached the predetermined current (S 207 : YES), the microcomputer  50  determines that the battery  2  is fully charged and outputs a high signal as the stop signal from the output port  51   a  to the photocoupler  4  to set the PWM control IC  23  in the stop state (step  208 ). 
         [0042]    After stopping the charging, the microcomputer  50  outputs a high signal as the charging state signal from the output port  51   a  to the transistor  128  to turn on. By turning on the transistor  128 , the FET  125  also turns on, and the reference voltage Vcc is applied to the LED  121  via the resistor  124 , causing the LED  121  to light up with the green color strongly (brightly) (step  209 ). 
         [0043]    Then, the microcomputer  50  determines whether the battery pack  2  is detached from the charging device  1  (S 210 ). If the battery pack  2  is detached from the charging device  1  (step  210 : YES), the processing returns to step  201 . 
         [0044]    As described above, when the charging is completed, a high voltage is applied to the LED  121  via the resistor  124 . Thus, the user who is distant from the charging device  1  can clearly understand that the charging has been completed. Furthermore, during the charging, the current is flowed through the LED  121  via the resistor  122 . The value of the current which is flowed thorough the LED  121  via the resister  123  is smaller than the value of the current which is flowed through the LED  121  via the resistor  124 . Thus, energy is saved. Furthermore, during the charging, the current is flowed via the resistor  122 . Thus, the orange color can be correctly displayed, since the green color is not too strong. 
         [0045]    Further, in the preferred embodiment, when it is required to flow a strong current to the LED  121 , the reference voltage Vcc is applied to the LED  121  via the resistor  124 . Thus, the strong current is prevented from flowing in the digital circuit such as the microcomputer  50 . 
         [0046]    While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.