Abstract:
A power charging system includes an embedded controller (EC), a control integrated circuit (IC), a current charging IC, and a power converter. The embedded controller outputs a pre-charging signal, a first charging signal, and a second charging signal according to the electricity quantity of the rechargeable battery. The control IC controls a plurality of switches to be on or off to generate a configuration of a plurality of configurations according to the received pre-charging signal, the received first charging signal, and the received second charging signal and correspondingly generates a voltage value according to the configuration. The current charging IC receives the voltage value and outputs a control signal. The power converter converts a direct current outputs to a charging current with a specific value according to the received control signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an electronic device and a power charging system thereof and, more particularly, to a power charging system occupying a smaller design space and having eight stage charging currents and a related electronic device thereof. 
       BACKGROUND OF THE INVENTION 
       [0002]      FIG. 1  is a circuit diagram showing a conventional power charging system. A power charging system  2  of a conventional electronic device  25  is connected between a power adaptor  4  and a lithium ion battery  6 , and it mainly includes a current charging integrated circuit (IC)  10 , a control circuit  12 , a power converter  14 , and an embedded controller (EC)  16 . The power charging the lithium ion battery  6  is from a direct current outputted by the power adaptor  4 , and the power adaptor  4  may supply power to the electronic device  25 . When the power adaptor  4  does not supply power to the electronic device  25 , the electricity quantity in the lithium ion battery  6  is supplied to an electronic system  20  of the electronic device  25  via the conduction of a power change-over switch (D 1 ). The electronic device may be a notebook computer system, a personal digital assistant (PDA), or a handheld telephone, and the lithium ion battery  6  is a rechargeable battery. 
         [0003]    To ensure the safety of charging, the practical electricity quantity of the lithium ion battery  6  should be detected at any time, the value of a charging current (Icharge) charging the lithium ion battery  6  should be adjusted according a detecting result. First, the EC  16  detects the practical electricity quantity in the lithium ion battery  6 , and a detecting input end (d) of the EC  16  receives a detecting signal. Afterward, a pre-charging signal PRECHG, a first charging signal BATSEL_ 2 P#, and a second charging signal BATSEL_ 4 P# are outputted to the control circuit  12  according to the result. Then, the control circuit  12  correspondingly changes the voltage of a charging current pin ADJ 2  of the current charging IC  10  according to the levels of the three signals. The current charging IC  10  outputs a control signal to the power converter  14  via an output pin OUT according to the voltage value received by the charging current pin ADJ 2 . The power converter  14  converts a direct current with a specific value outputted by the power adapter  4  to a charging current Icharge which may be dynamically adjusted to output to the lithium ion battery  6  to charge according to the received control signal. 
         [0004]    In respect of the current charging IC  10 , a charging current (Icharge) outputted to the lithium ion battery  6  may be generated via the following formulas. 
         [0005]    When Vadj 2  is between 0V to 0.075 volts (V), Icharge=0 A. 
         [0006]    When Vadj 2  is between 0.075V to Vref, Icharge=(Vadj 2 −0.075)/(25*RS 2 ). 
         [0007]    Wherein Vadj 2  is the voltage of the charging current pin, Vref is the voltage of the reference voltage pin VREF, Vref is 5V, and the maximum value of Vadj 2  cannot be more than 5V. 
         [0008]    Generally speaking, a period of charging the lithium ion battery  6  is divided into two stages, a pre-charging mode and a charging mode. When the EC  16  detects to know that the voltage of the lithium ion battery  6  is smaller than a specific value (such as 3V), the power charging system  2  enters into the pre-charging mode at that moment. In the pre-charging mode, the levels of the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# outputted by the EC  16  are (High, Low, Low), respectively. In this configuration, a high level pre-charging signal PRECHG received by a gate electrode of a MOS switch M 4  in the control circuit  12  makes the MOS switch M 4  on. The low level first charging signal BATSEL_ 2 P# and the low level second charging signal BATSEL_ 4 P# received by the gate electrodes of the MOS switches M 2  and M 3  make the MOS switches M 2  and M 3  off. The MOS switch M 4  which is on makes a resistor Rb first connected with a resistor R 4  in parallel and then connected with a resistor Ra in series, and thus the voltage Vref of the reference voltage pin VREF of the current charging IC  10  generates a partial voltage Vadj 2  with a specific value to the charging current pin ADJ 2 . At that moment, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the voltage Vadj 2  received by the charging current pin ADJ 2 , and the power converter  14  correspondingly generates the charging current (Icharge, usually 150 mA) to charge the lithium ion battery  6  according to the received control signal. 
         [0009]    When the voltage of the lithium ion battery  6  is increased from 3V to another specific value (such as 4.2V) via charging, the power charging system  2  enters the charging mode at that moment. In the charging mode, the level of the pre-charging signal PRECHG outputted by the EC  16  is always a low level (Low). At that moment, the EC  16  may detect the practical voltage of the lithium ion battery  6  and change the levels of the first charging signal BATSEL_ 2 P# and the second charging signal BATSEL_ 4 P# outputted to the gate electrodes of the MOS switches M 2  and M 3 , respectively, and thus the current charging IC  10  makes the power converter  14  generate the charging current Icharge with different values to the lithium ion battery  6  to charge via the control signal outputted to the power converter  14 . For example, when the level of the first charging signal BATSEL_ 2 P# is a low level and the level of the second charging signal BATSEL_ 4 P# is a high level according to the practical voltage of the lithium ion battery  6  detected by the EC  16 , the MOS switch M 3  which is on makes the resistor Rb first connected with resistor R 3  in parallel and then connected with the resistor Ra in series, and thus the voltage Vref of the reference voltage pin VREF of the current charging IC  10  generates another partial voltage Vadj 2  with a specific value to the charging current pin ADJ 2 . At that moment, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the voltage Vadj 2  received by the charging current pin ADJ 2 , and then the power converter  14  correspondingly generates the charging current (Icharge, such as 0.56 A) to the lithium ion battery  6  to charge according to the received control signal. Similarly, when the level of the first charging signal BATSEL_ 2 P# is a high level and the level of the second charging signal BATSEL_ 4 P# is a low level according to the practical voltage of the lithium ion battery  6  detected by the EC  16 , the MOS switch M 2  which is on makes the resistor Rb first connected with the resistor R 2  in parallel and then connected with the resistor Ra in series, and thus the voltage Vref of the reference voltage pin VREF of the current charging IC  10  generates another partial voltage Vadj 2  with a specific value to the charging current pin ADJ 2 . At that moment, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the voltage Vadj 2  received by the charging current pin ADJ 2 , and then the power converter  14  correspondingly generates the charging current (Icharge, such as 1.6 A) to the lithium ion battery  6  to charge according to the received control signal. Similarly, when the levels of the first charging signal BATSEL_ 2 P# and the second charging signal BATSEL_ 4 P# are both low levels according to the practical voltage of the lithium ion battery  6  detected by the EC  16 , the MOS switches M 2  and M 3  are both off. Thus, the voltage Vref of the reference voltage pin VREF of the current charging IC  10  generates another partial voltage Vadj 2  with a specific value to the charging current pin ADJ 2 . At that moment, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the voltage Vadj 2  received by the charging current pin ADJ 2 , and then the power converter  14  correspondingly generates the charging current (Icharge, such as 2.8 A) to the lithium ion battery  6  to charge according to the received control signal. 
         [0010]    To sum up, when the power charging system  2  is operated in the pre-charging mode, the configuration of the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# outputted by the EC  16  is (High, Low, Low). At that moment, the power charging system  2  generates the charging current with the specific value (Icharge, 150 mA) to charge the lithium ion battery  6 . When the power charging system  2  is operated at the charging mode, the configuration of the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# may be (Low, Low, High), (Low, High, Low), and (Low, Low, Low). At that moment, the power charging system  2  generates the charging current with the specific value (Icharge, 0.56 A, 1.6 A, or 2.8 A) to charge the lithium ion battery  6 .  FIG. 2  is a table showing charging currents Icharge correspondingly generated according to the configurations of a pre-charging signal, a first charging signal, a second charging signal. 
         [0011]    However, the change of the level of the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# outputted by the EC  16  may generate eight configurations. The control circuit  12  of the conventional power charging system  2  only uses the four configurations generated by the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, the second charging signal BATSEL_ 4 P# to correspondingly generate the four different partial voltages to the charging current pin ADJ 2  of the current charging IC  10 , and then only four corresponding control signals are generated to the power converter  14 , which causes that the power converter  14  only can generate fourth stage charging currents (150 mA, 0.56 A, 1.6 A, 2.8 A) to charge the lithium ion battery  6 . Thus, part of the configurations of the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# are wasted. Furthermore, the control circuit  12  mainly composed of the MOS switches M 2 , M 3 , and M 4  occupies too large design space of the power charging system  2 . 
       SUMMARY OF THE INVENTION 
       [0012]    A power charging system is connected between a power adaptor and a rechargeable battery, and the rechargeable battery is used for supplying power to an electronic system of an electronic device. The power charging system includes an embedded controller (EC), a control integrated circuit (IC), a current charging IC, and a power converter. The embedded controller is connected with the rechargeable battery and used for outputting a pre-charging signal, a received first charging signal, and a received second charging signal according to the electricity quantity of the rechargeable battery. The control IC controls a plurality of switches to be on or off to generate a configuration of a plurality of configurations according to the level of the received pre-charging signal, the first charging signal, and the second charging signal and correspondingly generates a voltage value according to the configuration. The current charging IC receives the voltage value via a charging current pin and outputs a control signal according to the voltage value. The power converter converts a direct current outputted by the power adaptor to a charging current with a specific value according to the received control signal to charge the rechargeable battery. 
         [0013]    The invention provides a power charging system, the power charging system may correspondingly change the voltage value of the charging current pin of the current charging IC according to eight configurations generated via the change of the levels of the received pre-charging signal, the first charging signal, and the second charging signal, and then eight stage charging currents may be generated, and thus the charging current is further subdivided. Additionally, since the control circuit in the conventional power charging system is replaced by the control IC according to the invention, the design space for the power charging system is further reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
           [0015]      FIG. 1  is a circuit diagram showing a circuit of a conventional power charging system; 
           [0016]      FIG. 2  is a table showing charging currents correspondingly generated according to the configurations of a pre-charging signal, a first charging signal, a second charging signal; and 
           [0017]      FIG. 3  is a circuit diagram showing a power charging system according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    A power charging system according to the invention mainly utilizes a control IC to replace a conventional control circuit  12 , and the control IC generates eight corresponding specific partial voltages to a charging current pin ADJ 2  of a current charging IC  10  according to eight configurations generated by a received pre-charging signal PRECHG, a first charging signal BATSEL_ 2 P#, and a second charging signal BATSEL_ 4 P#, and then the current charging IC  10  correspondingly outputs an eight stage control signal to a power converter  14 . Afterward, the power converter  14  correspondingly generates eight stage charging currents to a lithium ion battery  6  to charge according to the received control signal. As a result, the charging current is further subdivided, and the design space for the power charging system is reduced. 
         [0019]      FIG. 3  is a circuit diagram showing a power charging system according to an embodiment of the invention. A power charging system  30  in an electronic device  35  according to the invention is connected between the power adaptor  4  and a lithium ion battery  6 , and it mainly includes the current charging IC  10 , a control IC  32 , the power converter  14 , and the EC  16 . The power for charging the lithium ion battery  6  is from a direct current outputted by the power adaptor  4 . At the same time, the power adaptor  4  may supply power to the electronic device  35 . When the power adaptor  4  does not supply power to the electronic device  35 , the electricity quantity of the lithium ion battery  6  is supplied to the electronic system  20  of the electronic device  35  via a power change-over switch (D 1 ) which is on. Since the control IC  32  is connected between the current charging IC  10  and the EC  16 , the control IC  32  may receive the pre-charging signal PRECHG, the first charging signal BATSEL_ 2 P#, and the second charging signal BATSEL_ 4 P# outputted by the EC  16  for representing the practical electricity quantity of the lithium ion battery  6 . 
         [0020]    Moreover, a pin P 9  of the control IC  32  is connected with the charging current pin ADJ 2  of the current charging IC  10 . A pin P 10  is connected with a reference voltage pin VREF of the current charging IC  10 . A pin P 1 , a pin P 2 , a pin P 3 , a pin P 4 , a pin P 5 , a pin P 6 , a pin P 7 , and a pin P 8  are connected with ground via a resistor R 5 , a resistor R 6 , a resistor R 7 , a resistor R 8 , a resistor R 9 , a resistor R 10 , a resistor R 11 , and a resistor R 12 , respectively. A pin P 11 , a pin P 12 , a pin P 13  may receive the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16 . 
         [0021]    Additionally, in the control IC  32 , the pin P 9  is connected with the pin P 1 , the pin P 2 , the pin P 3 , the pin P 4 , the pin P 5 , the pin P 6 , the pin P 7 , and the pin P 8  via a switch S 1 , a switch S 2 , a switch S 3 , a switch S 4 , a switch S 5 , a switch S 6 , a switch S 7 , and a switch S 8 , respectively. The switch S 1 , the switch S 2 , the switch S 3 , the switch S 4 , the switch S 5 , the switch S 6 , the switch S 7 , and the switch S 8  are controlled to be on and off by the eight configurations (000, 001, 010, 011, 100, 101, 110, 111) composed of the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4 . That is, controlling the switch S 1 , the switch S 2 , the switch S 3 , the switch S 4 , the switch S 5 , the switch S 6 , the switch S 7  and switch  8  to be on or off may be realized by the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  via a multiplexer/demultiplexer. 
         [0022]    First, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a first configuration such as (000), the switch Si is on at that moment, and the other seven switches S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8  are OFF. The switch S 1  which is on makes the resistor R 5  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a first voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the first voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a first current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the first current value may be the charging current Icharge 150 mA outputted to the lithium ion battery  6  by the power charging system  30  operated in the pre-charging mode. 
         [0023]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a second configuration such as (001), the switch S 2  is on at that moment, and the other seven switches S 1 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8  are OFF. The switch S 2  which is on makes the resistor R 6  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a second voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the second voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a second current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the second current value may be the charging current Icharge with the second current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0024]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a third configuration such as (010), the switch S 3  is on at that moment, and the other seven switches S 1 , S 2 , S 4 , S 5 , S 6 , S 7 , S 8  are OFF. The switch S 3  which is on makes the resistor R 7  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a third voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the third voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a third current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the third current value may be the charging current Icharge with the third current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0025]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a fourth configuration such as (011), the switch S 4  is on at that moment, and the other seven switches S 1 , S 2 , S 3 , S 5 , S 6 , S 7 , S 8  are OFF. The switch S 4  which is on makes the resistor R 8  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series. Thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a fourth voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the fourth voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a fourth current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the fourth current value may be the charging current Icharge with the fourth current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0026]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a fifth configuration such as (100), the switch S 5  is on at that moment, and the other seven switches S 1 , S 2 , S 3 , S 4 , S 6 , S 7 , S 8  are OFF. The switch S 5  which is on makes the resistor R 9  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a fifth voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the fifth voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a fifth current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the fifth current value may be the charging current Icharge with the fifth current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0027]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a sixth configuration such as (101), the switch S 6  is on at that moment, and the other seven switches S 1 , S 2 , S 3 , S 4 , S 5 , S 7 , S 8  are OFF. The switch S 6  which is on makes the resistor R 10  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a sixth voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the sixth voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a sixth current value to charge the lithium ion battery  6  according to the received control signal. The charging current Icharge with the sixth current value may be the charging current Icharge with the sixth current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0028]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a seventh configuration such as (110), the switch S 7  is on at that moment, and the other seven switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 8  are OFF. The switch S 7  which is on makes the resistor R 11  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a seventh voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the seventh voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a seventh current value to the charge lithium ion battery  6  according to the received control signal. The charging current Icharge with the seventh current value may be the charging current Icharge with the seventh current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0029]    Similarly, when the EC  16  detects the practical voltage of the lithium ion battery  6  to make the pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4  outputted by the EC  16  in a eighth configuration such as (111), the switch S 8  is on at that moment, and the other seven switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7  are OFF. The switch S 8  which is on makes the resistor R 12  first connected with the resistor Rb in parallel and then connected with the resistor Ra in series, and thus the partial voltage of the reference voltage Vref of the reference voltage pin VREF of the current charging IC  10  at the charging current pin ADJ 2  is a eighth voltage, the current charging IC  10  outputs a corresponding control signal to the power converter  14  according to the eighth voltage received by the charging current pin ADJ 2  at that moment, and then the power converter  14  correspondingly generates the charging current Icharge with a eighth current value to the lithium ion charge battery  6  according to the received control signal. The charging current Icharge with the eighth current value may be the charging current Icharge with the eighth current value outputted to the lithium ion battery  6  by the power charging system  30  operated in the charging mode. 
         [0030]    To sum up, the control IC  32  of the power charging system  30  may make the charging current pin ADJ 2  of the current charging IC  10  generate eight voltages with different values according to the eight configurations (000, 001, 010, 011, 100, 101, 110, 111) composed of the received pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4 , and thus the power converter  14  generates eight stage charging currents Icharge to the lithium ion battery  6 . As a result, it may improve that the conventional power charging system  2  which only outputs four stage charging currents Icharge to the lithium ion battery  6  according to four configurations composed of the received pre-charging signal PRECHG, the first charging signal BATSEL_# 2 , and the second charging signal BATSEL_# 4 , and thus the charging current Icharge is further subdivided. Additionally, since the control circuit  12  in the conventional power charging system  2  is replaced by the control IC  32  in the power charging system  30 , the design space for the power charging system is reduced, and eight stage charging currents may be chosen. 
         [0031]    Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, the disclosure is not for limiting the scope of the invention. Persons having ordinary skill in the art may make various modifications and changes without departing from the scope and spirit of the invention. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments described above.