Abstract:
The invention discloses a power supply system for charging a rechargeable battery in a portable electronic device. The power supply system of the invention redefines an output curve of a power adapter, such that the power adapter can work in a maximum power region for a long time. When a system current plus a charging current exceed a maximum current limit of the power adapter, the power supply system of the invention will automatically lower the current for charging a battery, so as to prevent the power adapter from being shut down.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a power supply system and, more particularly, relates to a power supply system for charging a battery in a portable electronic device. When a system current plus a charging current exceed a maximum current limit of a power adapter, the power supply system of the invention will automatically reduce the current for charging the battery, so as to prevent the power adapter from being shut down. 
         [0003]    2. Description of the Prior Art 
         [0004]    In general, a portable electronic device (e.g. notebook) usually has a rechargeable battery. When the portable electronic device can not be supplied with power by a traditional power socket, it will be supplied with power by the battery to keep working. 
         [0005]    Referring to the  FIG. 1 ,  FIG. 1  is a schematic diagram illustrating a circuit of a power supply system  1  of the prior art. As shown in  FIG. 1 , when there is a traditional power socket, users can use an AC/DC adapter  10  to supply power for operating a system load  12  of a portable electronic device  2 . Additionally, the AC/DC adapter  10  can also supply power for charging a battery  16  by a DC/DC converter  14 . 
         [0006]    As shown in  FIG. 1 , an input current I 1  supplied by the AC/DC adapter  10  comprises a system current I 2  and a charging current I 3 . A constant power circuit  17  of the power supply system  1  has a resistance R 1  for detecting the input current I 1 . When the system current I 2  increases, the input current I 1  increases as well. Therefore, the voltage drop of the resistance R 1  achieves a default value VR 1 . Afterward, an operational amplifier  18  outputs signals to reduce the charging current I 3 , such that the input current I 1  will not exceed the default value. In other words, the maximum output current of the AC/DC adapter  10  is first used for supplying the system current I 2 , the remaining current is then used for supplying the charging current I 3 . However, since the power supply system  1  has to utilize the constant power circuit  17  to control the input current I 1 , the circuit design thereof is more complex. 
         [0007]    Referring to  FIG. 2 ,  FIG. 2  is a schematic diagram illustrating an output curve of the AC/DC adapter  10  shown in  FIG. 1 . In general, an output voltage of the AC/DC adapter  10  is constant. In other words, under normal situation, the AC/DC adapter  10  will work in a constant voltage region, as shown in  FIG. 2 . When a load is extraordinary large, the AC/DC adapter  10  will work in a protection against overload region. At the same time, the output voltage decreases while the output current increases. At last, the AC/DC adapter  10  will be shut down. In prior art, the minimum output voltage of the AC/DC adapter  10  usually does not be defined. Additionally, the protection against overload region is a protection against overload current, so the difference of protection against overload current between AC/DC adapters  10  is large, as lines S and T shown in  FIG. 2 . The AC/DC adapter  10  is usually protected by a primary circuit to be against overload and does not damage itself at a minimum cost. Therefore, the AC/DC adapter  10  cannot work in the protection against overload region for a long time. 
         [0008]    Referring to  FIG. 1 , the traditional power supply system  1  further comprises an ID detector  20  for detecting an ID signal provided by different AC/DC adapter  10  with different power. According to different ID, the ID detector  20  will output a corresponding signal variation VR 1 , such that the power supply system  1  can co-operate to different AC/DC adapter  10  with different power. However, the ID detector  20  increases the cost of the power supply system  1 . 
         [0009]    In short, the traditional power supply system  1  has the following disadvantages of: 1) a more complex circuit design; 2) unable to work in the protection against overload region for a long time, so the maximum power of the AC/DC adapter  10  can not be fully utilized; and 3) a higher cost, if the power supply system  1  is equipped with the ID detector  20 . Therefore, the scope of the invention is to provide a power supply system for solving the aforesaid problems. 
       SUMMARY OF THE INVENTION 
       [0010]    A scope of the invention is to provide a power supply system which re-defines an output curve of an AC/DC adapter, such that the AC/DC adapter can work in a maximum power region for a long time. Accordingly, the circuit design of the power supply system is simplified. 
         [0011]    According to a preferred embodiment, the power supply system of the invention is used for charging a battery in a portable electronic device. The power supply system comprises a power adapter and a charging current converter. The power adapter is used for supplying an input current. The input current comprises a system current and a charging current. The system current is used for operating the portable electronic device, and the charging current is used for charging the battery. The power adapter defines a first working region and a second working region. A minimum output voltage is set in the second working region. The power adapter supplies a constant output voltage in the first working region and a decreased output voltage in the second working region, wherein the decreased output voltage decreases from the constant output voltage to the minimum output voltage. 
         [0012]    In the aforesaid embodiment, when the input current exceeds a maximum current limit of the power adapter, an output voltage corresponding to the input current starts to decrease according to the decreased output voltage in the second working region. Further, an input voltage of the charging current converter decreases to decrease the charging current. Accordingly, when the portable electronic device is turned on, the maximum output current of the AC/DC adapter is first used for supplying the system current, and the remaining current is then used for supplying the charging current. 
         [0013]    Therefore, since the power supply system of the invention is not equipped with a constant power circuit, the circuit design is simplified. Additionally, according to the power supply system of the invention, the portable electronic device can co-operate to different AC/DC adapter with different power without an ID detector. Consequently, the cost is reduced. 
         [0014]    The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram illustrating a circuit of a power supply system  1  of the prior art; 
           [0016]      FIG. 2  is a schematic diagram illustrating an output curve of the AC/DC adapter  10  shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a schematic diagram illustrating a circuit of a power supply system  3  according to a preferred embodiment of the invention; 
           [0018]      FIG. 4  is a schematic diagram illustrating an output curve of the power adapter  30  shown in  FIG. 3 ; 
           [0019]      FIG. 5  is a schematic diagram illustrating a circuit of the power adapter  30  shown in  FIG. 3 ; and 
           [0020]      FIG. 6  is a timing diagram illustrating the power supply system  3  shown in  FIG. 3  during practical operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring to  FIG. 3 ,  FIG. 3  is a schematic diagram illustrating a circuit of a power supply system  3  according to a preferred embodiment of the invention. The power supply system  3  is used for charging a battery  36  in a portable electronic device  4 . In this embodiment, the power supply system  3  comprises a power adapter  30 , a charging current converter  34 , a constant current circuit  38 , a constant voltage circuit  40 , and a power adapter detecting circuit  42 . The portable electronic device  4  can be a notebook, a laptop, or the like. The power adapter  30  can be an AC/DC adapter, and the charging current converter  34  can be a DC/DC converter. The constant current circuit  38  is coupled between the battery  36  and the charging current converter  34 . The constant voltage circuit  40  is also coupled between the battery  36  and the charging current converter  34 . The power adapter detecting circuit  42  is coupled between the power adapter  30  and the charging current converter  34 . In this embodiment, the voltage of the power adapter detecting circuit  42  is set to be lower than the minimum voltage of the battery  36 . 
         [0022]    As shown in  FIG. 3 , the power adapter  30  is used for supplying an input current I 1 . The input current I 1  comprises a system current I 2  and a charging current I 3 . The system current I 2  is used for supplying power for operating a system load  32  of the portable electronic device  4 , such that a user can operate the portable electronic device  4 . Additionally, the charging current I 3  is used for charging the battery  36 . 
         [0023]    Referring to  FIG. 4 ,  FIG. 4  is a schematic diagram illustrating an output curve of the power adapter  30  shown in  FIG. 3 . As shown in  FIG. 4 , the output curve of the power adapter  30  defines a first working region A 1  and a second working region A 2 . A minimum output voltage is set in the second working region A 2 . The power adapter  30  supplies a constant output voltage in the first working region A 1  and a decreased output voltage in the second working region A 2 . The decreased output voltage decreases from the constant output voltage to the minimum output voltage. In other words, the first working region A 1  represents a constant voltage region of the power adapter  30 , and the second working region A 2  represents a maximum power region of the power adapter  30 . 
         [0024]    In this embodiment, the minimum output voltage is set to be 10V, and the constant output voltage is set to be 19V. Therefore, the decreased output voltage decreases from 19V to 10V, as shown in  FIG. 4 . 
         [0025]    Referring to  FIG. 5 ,  FIG. 5  is a schematic diagram illustrating a circuit of the power adapter  30  shown in  FIG. 3 . In this embodiment, the power adapter  30  comprises a voltage feedback circuit  300  and a current feedback circuit  302 . The voltage feedback circuit  300  is used for stabilizing an output voltage and providing a reference voltage. The current feedback circuit  302  is used for adjusting the maximum current limit of the power adapter  30  according to the reference voltage. It should be noticed that the current feedback circuit  302  is embedded in a secondary circuit of the power adapter  30 . 
         [0026]    As shown in  FIG. 5 , the voltage feedback circuit  300  supplies a reference voltage V_ref. After acquiring the reference voltage V_ref, the current feedback circuit  302  utilizes voltage-dividing resistances R 17  and R 19  to connect with a non-inverting input end of an operation amplifier  3020 . Afterward, a resistance R 8  responsible for detecting an output current connects with an inverting input end of the operation amplifier  3020  through a resistance R 20 . At last, an output voltage VA is adjusted by a resistance R 17 , such that the maximum power limit is achieved. 
         [0027]    For example, if the reference voltage V_ref is set to be 2.5V, the resistance R 16  is set to be 16.36 KΩ, and the resistance R 19  is set to be 1 KΩ, a voltage of the non-inverting input end of the operation amplifier  3020  is 2.5V/(R 16 +R 19 )*R 19 =0.144V. Additionally, if the resistance R 17  is set to be 224 KΩ, the resistance R 20  is set to be 1 KΩ, and the resistance R 8  is set to be 20 mΩ, the output current can be calculated by the following formula 1. 
         [0000]      the output current=(0.144 V −( VA /( R 17+ R 20)* R 20))/ R 8.  Formula 1 
         [0028]    Therefore, when the output voltage VA is set to be 19V, the output current will be 3A; when the output voltage VA is set to be 10V, the output current will be 5A, as the output curve shown in  FIG. 4 . Accordingly, designers can adjust the output curve of the power adapter  30  according to practical demands. 
         [0029]    Referring to  FIG. 3 ,  FIG. 4 , and  FIG. 6 ,  FIG. 6  is a timing diagram illustrating the power supply system  3  shown in  FIG. 3  during practical operation. 
         [0030]    At time T 1 , the system current I 2  starts to increase. 
         [0031]    At time T 2 , the input current I 1  achieves the maximum current limit (e.g.  3 A shown in  FIG. 4 ) of the power adapter  30 , and the output voltage of the power adapter  30  starts to decrease. 
         [0032]    During time T 2 -T 3 , the output voltage of the power adapter  30  starts to decrease, and the maximum current limit of the power adapter  30  starts to increase (e.g. from  3 A to  5 A shown in  FIG. 4 ). 
         [0033]    At time T 3 , the output voltage of the power adapter  30  nearly drops to the voltage of the battery  36 . The input voltage of the charging current converter  34  decreases, such that a default charging current can not be achieved. Therefore, the charging current I 3  starts to decrease. 
         [0034]    During time T 3 -T 4 , the system current I 2  continuously increases, so the charging current I 3  decreases. Therefore, the input current I 1  is equal to the maximum current limit of the power adapter  30 . 
         [0035]    During time T 4 -T 5 , the charging current I 3  is equal to the maximum current limit (i.e. the input current I 1 ) of the power adapter  30  minus the system current I 2 . In other words, the current remained after consumption of the system load  32  of the portable electronic device  4  is used for charging the battery  36 . 
         [0036]    At time T 5 , the system current I 2  starts to decrease. 
         [0037]    During time T 5 -T 6 , the system current I 2  continuously decreases, so the charging current I 3  increases. Therefore, the input current I 1  is equal to the maximum current limit of the power adapter  30 . 
         [0038]    At time T 6 , the charging current I 3  achieves a default value and stops to increase. 
         [0039]    During time T 6 -T 7 , the system current I 2  continuously decreases. Since the input current I 1  is lower than the maximum current limit of the power adapter  30 , the output voltage of the power adapter  30  starts to increase again. 
         [0040]    At time T 7 , the output voltage of the power adapter  30  increases to a maximum voltage. 
         [0041]    During time T 7 -T 8 , the system current I 2  continuously decreases, and the charging current I 3  keeps constant. Therefore, the input current I 1  is lower than the maximum current limit of the power adapter  30 . 
         [0042]    In short, when the input current I 1  (i.e. the system current I 2  plus the charging current I 3 ) is exceeding the maximum current limit of the power adapter  30 , the power supply system  3  of the invention will automatically decrease the charging current I 3 . Accordingly, when the portable electronic device  4  is turned on, the power remained after consumption of the system load  32  can be fully supplied for charging the battery  36 . 
         [0043]    Referring to the following Table 1 and Table 2, Table 1 shows comparison of an AC/DC adapter (a power adapter) between the invention and prior art, and Table 2 shows comparison of a portable electronic device between the invention and prior art. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 AC/DC adapter 
                 Prior art 
                 The invention 
               
               
                   
               
             
             
               
                 voltage feedback circuit 
                 includes 
                 includes 
               
               
                 current feedback circuit 
                 not necessary 
                 necessary 
               
               
                 whether the adapter can 
                 no 
                 yes 
               
               
                 work in the maximum 
               
               
                 power region for a long 
               
               
                 time 
               
               
                 output voltage under 
                 keeps constant 
                 decreases after 
               
               
                 normal situation 
                   
                 achieving the 
               
               
                   
                   
                 maximum current limit 
               
               
                 where is the current 
                 primary or secondary 
                 secondary circuit 
               
               
                 feedback circuit 
                 circuit 
               
               
                 embedded 
               
               
                 minimum output voltage 
                 not defined 
                 need to define 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Portable electronic 
                   
                   
               
               
                 device 
                 Prior art 
                 The invention 
               
               
                   
               
             
             
               
                 constant power circuit 
                 includes 
                 not include 
               
               
                 ID detecting circuit 
                 depends on practical 
                 not include 
               
               
                   
                 demand 
               
               
                 voltage detecting point 
                 higher than the 
                 lower than the 
               
               
                 of AC/DC adapter 
                 maximum voltage of 
                 minimum voltage of 
               
               
                   
                 the battery 
                 the battery 
               
               
                 input voltage under 
                 keeps constant 
                 decreases after 
               
               
                 normal situation 
                   
                 achieving the 
               
               
                   
                   
                 maximum current limit 
               
               
                 charging current 
                 linear or switch mode 
                 linear or switch mode 
               
               
                 converter 
               
               
                   
               
             
          
         
       
     
         [0044]    Compared to the prior art, since the power supply system of the invention is not equipped with the constant power circuit, the circuit design is simplified. Additionally, according to the power supply system of the invention, the portable electronic device can co-operate to different AC/DC adapter with different power without an ID detector. Therefore, the cost is reduced. 
         [0045]    With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.