Patent Publication Number: US-2006012339-A1

Title: Method and system for charging battery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 2004-0055955, filed on Jul. 19, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method and a system for charging a battery, and more particularly, to a method and a system for stably and fully charging a battery.  
      2. Description of the Related Art  
      A portable electronic appliance including a portable computer such as a notebook personal computer, a personal digital assistant (PDA), a handheld personal computer, or the like; a portable display apparatus; a camcorder; etc. employs a battery as a power supplying system while being carried. Here, a rechargeable secondary battery is generally used as the battery, wherein the battery is recharged with power supplied through an adapter.  
      Technology related to the battery has become increasingly important because the battery is essential to the portable electronic appliance when the portable electronic appliance is used while being carried, or otherwise used remotely by a user.  
      One important technological aspect related to the battery is the ability to prevent the battery from overcharging. In the technology of preventing the battery from overcharging, constant current is initially applied to charge the battery, and then the current is decreased when the voltage charged in the battery is beyond a predetermined level, thereby controlling the voltage charged in the battery to not be increased any further. Generally, the former period is called a constant current charging mode, and the latter period is called a constant voltage charging mode.  
      In this conventional battery charging method, the voltage of the power supplied to the battery is measured while the battery is charged, so that the voltage of the power charged in the battery is determined. However, the voltage of the power supplied to the battery is generally different from the voltage of the power actually charged in the battery.  
      Therefore, in the case of the battery charged according to the conventional charging method, even though it is determined that the battery is fully charged with the supplied power, the battery is likely to be overcharged or not fully charged due to the difference between the supplied voltage and the charged voltage.  
      When the battery is overcharged, the battery itself may be damaged. Conversely, when the battery is not fully charged, the amount of charging/discharging the battery is wastefully increased, and therefore the life span of the battery is reduced.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an aspect of the present invention to provide a method and a system for charging a battery, in which a voltage actually charged in the battery is measured while the battery is charged, so that the battery is stably and fully charged.  
      The foregoing and/or other aspects of the present invention are achieved by providing a method for charging a battery, comprising: (a) stopping a charging of the battery after the battery is charged for a predetermined unit charging time; (b) measuring a voltage charged in the battery after a lapse of a stabilizing time from the stoppage of the charging of the battery in (a); (c) determining whether a voltage difference between the currently measured voltage of the battery and a just previously measured voltage thereof is within a predetermined reference value while (a) and (b) are repeated; and (d) stopping the charging of the battery after (a), (b), (c) are repeated until the voltage difference is within the reference value by a predetermined number of times.  
      According to an aspect of the present invention, the reference value includes 0.  
      According to an aspect of the present invention, the method further comprises: (e) charging the battery by a constant current charging mode; and (f) charging the battery by a constant voltage charging mode, wherein (a), (b), (c), (d) are performed while (f) is performed.  
      According to another aspect of the present invention, the method further comprises: (e) charging the battery by a constant current charging mode; and (f) charging the battery by a constant voltage charging mode, wherein (a), (b), (c), (d) are performed while (f) is performed.  
      The foregoing and/or other aspects of the present invention are also achieved by providing a system for charging a battery, comprising: the battery; a battery charger charging the battery; a battery voltage measurer measuring voltage charged in the battery; and a controller controlling the battery charger to charge the battery on the basis of the measured voltage of the battery voltage measurer, the controller (a) controlling the battery charger to stop charging the battery after the battery is charged for a predetermined unit charging time; (b) controlling the battery voltage measurer to measure voltage charged in the battery after a lapse of a stabilizing time from the stoppage of charging of the battery; (c) determining whether a voltage difference between the voltage of the battery currently measured by the battery voltage measurer and a voltage thereof just previously measured by the battery voltage measurer is within a predetermined reference value while (a) and (b) are repeated; and (d) stopping the charging of the battery after (a), (b), (c) are repeated until the voltage difference is within the reference value by a predetermined number of times.  
      According to an aspect of the present invention, the reference value includes 0.  
      According to an aspect of the present invention, the controller controls the battery charger to charge the battery by a constant current charging mode while the battery is initially charged, and controls the battery charger to charge the battery by a constant voltage charging mode when the charged voltage of the battery measured by the battery voltage measurer is beyond a predetermined reference voltage, and (a), (b), (c), (d) are performed while the battery charger charges the battery by the constant voltage charging mode.  
      According to an aspect of the present invention, the controller controls the battery charger to charge the battery by a constant current charging mode while the battery is initially charged, and controls the battery charger to charge the battery by a constant voltage charging mode when the charged voltage of the battery measured by the battery voltage measurer is beyond a predetermined reference voltage, and (a), (b), (c), (d) are performed while the battery charger charges the battery by the constant voltage charging mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a control block diagram of a battery charging system according to an embodiment of the present invention;  
       FIG. 2  is a control flowchart of a battery charging method according to a first embodiment of the present invention;  
       FIG. 3  is a control flowchart of a battery charging method according to a second embodiment of the present invention; and  
       FIG. 4  is a graph illustrating battery voltage, charging current, and charging voltage while a battery is charged in the battery charging system according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
       FIG. 1  is a control block diagram of a battery charging system according to an embodiment of the present invention. As shown therein, a battery charging system comprises a battery  1 , a power supply  3 , a battery charger  2 , a battery voltage measurer  4  and a controller  5 .  
      According to an embodiment of the present invention, a secondary battery rechargeable by the battery charger  2  is used as the battery  1 . For example, the battery  1  includes a rechargeable lithium-ion battery, and other rechargeable secondary batteries.  
      The power supply  3  supplies power for charging the battery  1  to the battery charger  2 . According to an embodiment of the present invention, the power supply  3  includes an AC/DC adapter converting commercial AC power into DC power having a predetermined voltage level and transmitting it to the battery charger  2 . In addition, the power supply  3  may include a DC/DC adapter using DC power as input power like a cigar lighter socket for vehicles.  
      The battery charger  2  converts the power supplied from the power supply  3  into a charging voltage for the battery  1 , and charges the battery  1  with the charging voltage. Here, the battery charger  2  is controlled by the controller  5  to start or stop charging the battery  1 .  
      The battery voltage measurer  4  is controlled by the controller  5  to measure voltage charged in the battery  1 . According to an embodiment of the present invention, the battery voltage measurer  4  measures the voltage applied to a power terminal Vcc of the battery  1  when the battery charger  2  stops charging the battery  1 , thereby measuring the voltage actually charged in the battery  1 .  
      The controller  5  controls the battery charger  2  and determines whether the battery  1  is charged fully or not. Further, the controller  5  controls the battery charger  2  to charge the battery  1  on the basis of the measured result of the battery voltage measurer  4 .  
      Hereinbelow, a battery charging method according to a first embodiment of the present invention will be described with reference to  FIG. 2 .  
      First, when the power is supplied from the power supply  3 , at operation S 10 , the controller  5  controls the battery charger  2  to start charging the battery  1 . At this operation, the controller  5  initializes a predetermined register value (count) to “0”.  
      Then, at operation S 11 , the controller  5  determines whether a unit charging time is elapsed after the battery charger  2  starts charging the battery  1 . When the unit charging time is elapsed, at operation S 12 , the controller  5  controls the battery charger  2  to stop charging the battery  1 .  
      Then, at operation S 13 , the controller  5  determines whether a stabilizing time is elapsed after the battery charger  2  stops charging the battery  1 . When the stabilizing time is elapsed, at operation S 14 , the controller  5  controls the battery voltage measurer  4  to measure the voltage currently charged in the battery  1 .  
      Here, the stabilizing time is used for postponing the measurement of the battery voltage measurer  4  until the remaining power of the charging power supplied from the battery charger  2  to the battery  1  has a minimum effect on the measured voltage charged in the battery  1 . Therefore, the battery voltage measurer  4  can measure the voltage of the power charged in the battery  1  more accurately.  
      Then, at operation S 15 , the controller  5  checks whether there is a just previously measured voltage. When there is no just previously measured voltage, at operation S 20 , the controller  5  controls the battery charger  2  to restart charging the battery  1 , and performs the operations S 11  through S 14  again.  
      On the other hand, when there is a just previously measured voltage, at operation S 16 , the controller  5  checks whether a voltage difference between the voltage measured at the operation S 14  and the just previously measured voltage is within a predetermined reference value, defined by Vref.  
      In one embodiment, the value Vref is “0”. That is, the controller  5  checks whether the voltage measured at the operation S 14  is equal to the just previously measured voltage.  
      In the case where the voltage difference between the currently measured voltage of the battery  1  and the just previously measured voltage is within the reference value Vref (e.g., when the reference voltage is “0”, that is, when the currently measured voltage of the battery  1  is equal to the just previously measured voltage), at operation S 16 , the register value (count) is increased by “1”.  
      Then, at operation S 18 , the controller  5  checks whether the register value (count) is equal to a predetermined reference number. When the register value (count) is not equal to the reference number, at operation S 20 , the controller  5  controls the battery charger  2  to restart charging the battery  1 , and performs the operations S 11  through S 18  again.  
      On the other hand, when the register value (count) is equal to the reference number, at operation S 19 , the controller  5  controls the battery charger  2  to finish charging the battery  1 .  
      Hereinbelow, a battery charging method according to a second embodiment of the present invention will be described with reference to  FIGS. 3 and 4 .  
      According to the second embodiment of the present invention, the controller  5  controls the battery charger  2  to charge the battery  1  by a constant current charging mode while the battery  1  is initially charged. Further, when the charged voltage of the battery  1  measured by the battery voltage measurer  4  is beyond a predetermined reference voltage, the controller  5  controls the battery charger  2  to charge the battery  1  by a constant voltage charging mode.  
      Here, the constant current charging mode means that the battery charger  2  charges the battery  1  with a constant charging current C (refer to  FIG. 4 ). That is, as shown in a period of CC in  FIG. 4 , the charging current C supplied from the battery charger  2  to the battery  1  is constant, while a voltage A (refer to  FIG. 4 ) charged to the battery  1  is increased.  
      Further, the constant voltage charging mode means that the battery charger  2  charges the battery  1  with a constant charging voltage B (refer to  FIG. 4 ). That is, as shown in a period of CV in  FIG. 4 , the charging current C supplied from the battery charger  2  to the battery  1  is gradually decreased, while the charging voltage B supplied to the battery  1  is constant.  
      Referring to  FIG. 3 , when the power is supplied from the power supply  3 , at operation S 30 , the controller  5  controls the battery charger  2  to start charging the battery  1 . At operation S 31 , the controller  5  controls the battery charger  2  to charge the battery  1  by the constant current charging mode.  
      At operation S 32 , the controller  5  determines whether to charge the battery  1  by the constant voltage charging mode or not on the basis of the charged voltage of the battery  1  measured by the battery voltage measurer  4 . At this time, the charged voltage measured by the battery voltage measurer  4  may be a voltage measured after stopping charging the battery  1  or a voltage measured while the battery  1  is charged.  
      When the charged voltage of the battery  1  measured by the battery voltage measurer  4  is beyond the reference voltage, at operation S 33 , the controller  5  controls the battery charger  2  to charge the battery  1  by the constant voltage charging mode. At this operation S 33 , the controller  5  initializes a predetermined register value (count) into “0”.  
      Then, at operation S 34 , the controller  5  determines whether a unit charging time has elapsed after the battery charger  2  starts charging the battery  1  by the constant voltage charging mode. When the unit charging time has elapsed, at operation S 35 , the controller  5  controls the battery charger  2  to stop charging the battery  1 .  
      Then, at operation S 36 , the controller  5  determines whether a stabilizing time has elapsed after the battery charger  2  stops charging the battery  1 . When the stabilizing time has elapsed, at operation S 37 , the controller  5  controls the battery voltage measurer  4  to measure the voltage currently charged in the battery  1 .  
      Then, at operation S 38 , the controller  5  checks whether there is a just previously measured voltage. When there is no just previously measured voltage, at operation S 43 , the controller  5  controls the battery charger  2  to restart charging the battery  1 , and performs the operations S 34  through S 37  again.  
      On the other hand, when there is a just previously measured voltage, at operation S 39 , the controller  5  checks whether voltage difference between the voltage measured at the operation S 37  and the just previously measured voltage is within a predetermined reference value Vref.  
      In the case where, the voltage difference between the currently measured voltage of the battery  1  and the just previously measured voltage is within the reference voltage Vref (e.g., when the reference voltage is “0”, that is, when the currently measured voltage of the battery  1  is equal to the just previously measured voltage), at operation S 40 , the register value (count) is increased by “1”.  
      Then, at operation S 41 , the controller  5  checks whether the register value (count) is equal to a predetermined reference number. When the register value (count) is not equal to the reference number, at operation S 43 , the controller  5  controls the battery charger  2  to restart charging the battery  1 , and performs the operations S 34  through S 41  again.  
      On the other hand, when the register value (count) is equal to the reference number, at operation S 42 , the controller  5  controls the battery charger  2  to finish charging the battery  1 .  
      Thus, after the battery  1  is charged during the unit charging time, the voltage charged in the battery  1  is measured while the battery  1  is stopped from being charged, thereby correctly measuring the voltage actually charged in the battery  1 .  
      Further, the currently charged voltage measured by the foregoing method is compared with the just previously measured voltage, and thus the battery  1  is stopped from being charged when the voltage difference therebetween is within the reference value Vref by a predetermined number of times. Hence, the battery  1  is fully and stably charged.  
      As described above, the present invention provides a method and a system for charging a battery, in which voltage actually charged in the battery is measured while the battery is charged, so that the battery is stably and fully charged.  
      Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.