Abstract:
The present invention provides a charging device capable of reducing the number of power elements required for setting a charging current, thereby achieving a reduction in size and a low manufacturing cost. A circuit structure for a main charging is a main circuit structure, and a setting unit for setting a weak current is incorporated into the circuit structure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a charging device, and more particularly, to a charging device capable of performing main charging on a secondary battery by supplying a normal current to the secondary battery as a charging current and of performing trickle charging on the secondary battery by supplying a weak current to the secondary battery as the charging current.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, there has been disclosed a charging device having a function for mainly charging a secondary battery by supplying a normal current (a large current) to the secondary battery as a charging current and a function for trickle-charging the secondary battery by supplying a weak current to the secondary battery as the charging current.  
         [0005]     In general, when it is impossible for a secondary battery to generate the original electromotive force due to the deterioration of the performance of the secondary battery, the trickle charging is performed to restore the original performance of the secondary battery.  
         [0006]      FIG. 2  is a circuit diagram illustrating a circuit structure of a conventional charging device  1  having the trickle charging function. The charging device  1  has a main charging circuit  3  for performing the main charging on a secondary battery  2  and a trickle charging circuit  4  for performing the trickle charging on the secondary battery  2 .  
         [0007]     In the main charging circuit  3 , a charging current detecting resistor  7  is provided on the downstream side of a terminal  6  of a power source  5 , and the output side of the charging current detecting resistor  7  is connected to an inverting input terminal of an operational amplifier  8  through a resistor r 1 . The operational amplifier  8  controls the value of the charging current while detecting the current flowing through the charging current detecting resistor  7 .  
         [0008]     Meanwhile, a non-inverting input terminal of the operational amplifier  8  is connected to the ground through a resistor r 2 . In addition, a resistor r 3  is provided between the non-inverting input terminal of the operational amplifier  8  and the input side of the charging current detecting resistor  7 .  
         [0009]     Further, the output side of the charging current detecting resistor  7  is connected to an emitter of a power transistor Tr 1  serving as a power element for controlling the supply of the normal current to the secondary battery  2 , and a collector of the power transistor Tr 1  is connected to an anode of the secondary battery  2 . In addition, a resistor r 4  is provided between a base and the emitter of the power transistor Tr 1 .  
         [0010]     Furthermore, the base of the power transistor Tr 1  is connected to an emitter of a transistor Tr 2  for controlling a base current of the power transistor Tr 1 , and a collector of the transistor Tr 2  is connected to an output terminal of the operational amplifier  8  through a resistor r 5 . In addition, a resistor r 6  is provided between a base and the emitter of the transistor Tr 2 .  
         [0011]     Moreover, an end of a resistor r 7  is connected to the base of the transistor Tr 2 , and the other end of the resistor r 7  is connected to a collector of a transistor Tr 3  for controlling the base current of the transistor Tr 2 .  
         [0012]     An emitter of the transistor Tr 3  is connected to the ground, and a base thereof is connected through a resistor r 8  to a power supply terminal  10  for inputting a base current. In addition, a resistor r 9  is provided between the base and the emitter of the transistor Tr 3 .  
         [0013]     Further, in the trickle charging circuit  4 , a resistor r 10  is provided on the downstream side of the terminal  6  of the power source  5 , and the output side of the resistor r 10  is connected to an emitter of a power transistor Tr 4  serving as a power element for controlling the supply of the weak current to the secondary battery  2 .  
         [0014]     A collector of the power transistor Tr 4  is connected to the anode of the secondary battery  2 , and a diode  11  is provided between a base of the power transistor Tr 4  and the downstream side of the terminal  6  of the power source  5 . In addition, an end of a resistor r 11 , is connected to the base of the power transistor Tr 4 , and the other end of the resistor r 11 l is connected to a collector of a transistor Tr 5  for controlling the base current of the power transistor Tr 4 .  
         [0015]     A base of the transistor Tr 5  is connected to a base current input terminal  12  through a resistor r 12 . In addition, a resistor r 13  is connected between an emitter of the transistor Tr 5  and an end of the resistor r 12  connected to the base thereof. Further, the collector of the transistor Tr 5  is connected to the ground.  
         [0016]     According to the charging device having the above-mentioned structure, when the main charging is performed on the secondary battery  2 , a base current is supplied to the transistor Tr 3  such that the transistors Tr 3  and Tr 2  and the power transistor Tr 1  are turned on.  
         [0017]     Then, a normal current of about 700 mA is supplied as the charging current from the power source  5  to the secondary battery  2  through the emitter and the collector of the power transistor Tr 1 , thereby performing the main charging on the secondary battery  2 .  
         [0018]     In this case, since a base current is not supplied to the base of the transistor Tr 5 , the transistor Tr 5  and the power transistor Tr 4  are maintained in an off state.  
         [0019]     Subsequently, when the trickle charging is performed on the secondary battery  2 , the base current is supplied to the base of the transistor Tr 5  in a state in which the power transistor Tr 1  and the transistors Tr 2  and Tr 3  are off, so that the transistor Tr 5  and the power transistor Tr 4  are turned on.  
         [0020]     Then, a weak current of about 50 mA is supplied as the charging current from the power source  5  to the secondary battery  2  through the emitter and the collector of the power transistor Tr 4 , thereby performing the trickle charging on the secondary battery  2  (for example, see Japanese Unexamined Patent Application Publication No. 5-284664).  
         [0021]     However, in the conventional charging device  1 , the main charging circuit  3  is separately arranged from the trickle charging circuit  4 . Therefore, the circuits must respectively have expensive power transistors Tr 1  and Tr 4  for controlling the charging current (the normal current or the weak current), which causes an increase in the costs of manufacturing the charging device.  
         [0022]     Further, since the power transistors Tr 1  and Tr 4  in the respective circuits through which the charging current flows have high heating values, it is necessary that radiators (not shown) for radiating heat generated from the power transistors Tr 1  and Tr 4  be provided to the power transistors. Tr 1  and Tr 4  separately, which causes an increase in the number of components and an increase in manufacturing costs.  
       SUMMARY OF THE INVENTION  
       [0023]     Accordingly, the present invention is designed to solve the above-mentioned problems, and it is an object of the present invention to provide a charging device capable of reducing the number of power elements required for setting a charging current, thereby achieving a reduction in size and a low manufacturing cost.  
         [0024]     In order to achieve the above object, the present invention provides a charging device comprising: a power source for supplying a charging current to a secondary battery; an operational amplifier for controlling the supply of the charging current by the power source; and a power element for controlling the supply of the charging current to the secondary battery. Here, a main charging is performed on the secondary battery by supplying a normal current to the secondary battery as the charging current, and a trickle charging is performed on the secondary battery by supplying a weak current to the secondary battery as the charging current. Further, a circuit structure for the main charging is a main circuit structure, and a setting unit for setting the weak current is incorporated into the main circuit structure.  
         [0025]     Therefore, according to the charging device having the above-mentioned structure, a function for controlling the supply of the weak current can be practically complemented with the main charging circuit. Thus, it is possible to reduce the number of control elements required for controlling the charging current.  
         [0026]     Further, in the charging device according to the present invention, the setting unit sets the weak current by adjusting an offset of the operational amplifier.  
         [0027]     According to the charging device having the above-mentioned structure, it is possible to easily set the weak current.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  is a circuit diagram illustrating a charging device according to an embodiment of the present invention; and  
         [0029]      FIG. 2  is a circuit diagram illustrating an example of a conventional charging device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     Hereinafter, a charging device according to an embodiment of the present invention will be described with reference to  FIG. 1 .  
         [0031]     In  FIG. 1 , the components having substantially the same basic structure as those in a conventional charging device shown in  FIG. 2  have the same reference numerals.  
         [0032]     As shown in  FIG. 1 , a charging device  15  according to the present embodiment comprises a power source  5  for supplying the charging current to a secondary battery  2 , an operational amplifier  8  for controlling the supply of the charging current by the power source  5 , and a power transistor Tr 1  serving as a power element for controlling the supply of the charging current to the secondary battery  2 , which is basically the same structure as that of the conventional charging device.  
         [0033]     Meanwhile, in the conventional charging device, a main charging circuit  3  for performing main charging on the secondary battery  2  is separately arranged from a trickle charging circuit  4  for performing trickle charging on the secondary battery  2 . However, in the charging device  15  according to the present embodiment, these two circuits are integrated into one circuit, and a circuit structure for the main charging is a main circuit structure.  
         [0034]     In other words, the charging device  15  according to the present embodiment does not have a power transistor Tr 4 , a transistor Tr 5 , a diode  11 , and resistors r 10 , r 11 , r 12 , and r 13  which constitute the conventional trickle charging circuit  4 .  
         [0035]     In the charging device  15 , instead of the above-mentioned elements, a setting unit  16  is provided between a terminal  6  of the power source  5  and an inverting input terminal of the operational amplifier  8  to set a weak current when the trickle charging is performed on the secondary battery  2 .  
         [0036]     The setting unit  16  performs the setting of the weak current by adjusting the offset of the operational amplifier  8 , that is, the input offset voltage (the error voltage) between the input terminals of the operational amplifier  8 . In addition, when the volume of the setting unit  16  is small, it is possible to manufacture the charging device  15  at a lower cost.  
         [0037]     Further, a resistor r 14  is provided between the inverting input terminal of the operational amplifier  8  and the setting unit  16 .  
         [0038]     Furthermore, a collector of a transistor Tr 6  for switching between the main charging and the trickle charging is connected to the input side of a resistor r 2  connected to a non-inverting input terminal of the operational amplifier  8 . In addition, a resistor r 15  is connected to a base of the transistor Tr 6 , and a resistor r 16  is provided between an emitter and the base thereof.  
         [0039]     According to this structure, it is possible for the main charging circuit to practically have a function for controlling the supply of a weak current by slightly changing the structure of the main charging circuit, that is, by providing the setting unit  16 . Therefore, it is possible to reduce the number of control elements required for controlling the charging current.  
         [0040]     Moreover, it is possible to simply set the weak current by adjusting the offset of the operational amplifier.  
         [0041]     Next, the effects of the present embodiment will be described.  
         [0042]     According to the charging device  15  having the above-mentioned structure, when the main charging is performed on the secondary battery, a base current is supplied to a transistor Tr 3 , so that the transistor Tr 3 , transistor Tr 2  and the power transistor Tr 1  are turned on.  
         [0043]     Further, the base current is supplied to the base of the transistor Tr 6  to turn on the transistor Tr 6 .  
         [0044]     Then, a normal current of about 700 mA is supplied as the charging current from the power source  5  to the secondary battery  2  through the emitter and the collector of the power transistor Tr 1 , thereby performing the main charging on the secondary battery  2 .  
         [0045]     Subsequently, when the trickle charging is performed on the secondary battery  2 , the transistor Tr 6  is turned off, and the offset of the operational amplifier  8  is adjusted by the setting unit  16 .  
         [0046]     Then, a weak current of about 50 mA is supplied as the charging current from the power source  5  to the secondary battery  2  through the emitter and the collector of the power transistor Tr 1 , thereby performing the trickle charging on the secondary battery  2 .  
         [0047]     Therefore, according to the present embodiment, it is possible to reduce the number of power transistors, which are expensive power elements having a high heating value. Thus, it is possible to obtain the charging device  15  having a low manufacturing cost and to reduce the size of the device.  
         [0048]     Furthermore, the present invention is not limited to the above-mentioned embodiment, but variable modifications and changes may be made by one skilled in the art without departing from the scope or spirit of the present invention.