CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of Taiwan application serial no. 99124213, filed Jul. 22, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a power system and, more particularly, to an adaptor which supplies power to an electronic device according to whether the electronic device has a battery or not or the operation state of the electronic device. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 1  is a schematic diagram showing that a conventional adaptor  12  supplies power to an electronic device  10  (such as a notebook computer, a mobile phone or a digital camera). The electronic device  10  mainly includes a host  102  and a battery  104 , and the battery  104  is a chargeable battery. The adaptor  12  is connected to an alternating current (AC) voltage to receive the AC voltage AC_in, and the adaptor  12  is connected to the electronic device  10  to supply a direct current (DC) voltage DC_in to the electronic device  10 . 
         [0006]    As long as the conventional adaptor  12  is connected to the AC voltage, the adaptor  12  supplies the DC voltage DC_in to the electronic device  10  continuously regardless of the state of the host  102  and whether the battery  104  is fully charged or not, resulting in an power waste in the electronic elements of the adaptor  12 . 
         [0007]    For example, when the electronic device  10  is not configured with the battery  104 , and the host  102  is at a power off state, once the adaptor  12  is connected between the AC voltage and the electronic device  10 , the conventional adaptor  12  keeps supplying a constant DC voltage DC_in to the host  102 , resulting in the power waste. 
         [0008]    When the electronic device  10  is not configured with the battery  104  and the host  102  is at a hibernation state or a sleep state, once the adaptor  12  is connected between the AC voltage and the electronic device  10 , the conventional adaptor  12  still keeps supplying the constant DC voltage to the host  102 . 
         [0009]    In general, when the host  102  is at different states (a standby state, a hibernation state, a sleep state, an operation state, or other states), the needed minimum voltages are different. However, the conventional adaptor  12  still supplies the constant DC voltage DC_in to the host  102 , resulting in the power waste. 
         [0010]    Similarly, when the electronic device  10  is configured with the battery  104  and the host  102  is at the power off state, once the adaptor  12  is connected between the AC voltage and the electronic device  10 , the adaptor  12  keeps supplying the DC voltage to the electronic device  10  for charging the battery  104 . However, when the battery  104  is fully charged, the adaptor  12  still keeps supplying the DC voltage DC_in to the host  102 , which also results in the power waste. 
         [0011]    Moreover, the method of using a charger of the conventional adaptor to charge the battery may also waste the power.  FIG. 2  is a schematic diagram showing that the charger  14  (such as a mobile phone or a digital camera charger) of the conventional adaptor charges a battery  104 . As shown in  FIG. 2 , once the adaptor  12  is connected between the AC voltage and the battery  104 , even if the battery  104  is fully charged, the adaptor  12  still keeps supplying power to the battery  104 , also resulting in the power waste. 
         [0012]    In sum, no matter the host is at the power off state or the standby state (the hibernation state, the sleep state, the operation state or other states), or whether the battery is fully charged or not, the conventional adaptor keeps supplying a constant voltage to the electronic device at the standby state, resulting in the power waste. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    An adaptor with power saving function is provided. It adjusts the adaptor voltage supplied to an electronic device according to whether the electronic device has a battery, an operation state of the electronic device and whether the battery is fully charged or not, which saves power. 
         [0014]    A power system including an electronic device and an adaptor is provided. The electronic device includes a host, a state generator. The host has a plurality of states and generates a plurality of state signals corresponding the plurality of states. The state generator is electrically connected to the host, receives the state signals and generates a control signal according to the state signals. The adaptor is connected to an AC voltage and has a state receiving terminal to receive the control signal. The adaptor generates a DC voltage to the electronic device according to the control signal. 
         [0015]    Since the power system includes the adaptor and the state generator, the state generator adjusts the voltage supplied to an electronic device according to whether the electronic device has a battery, the operation state of the electronic device and whether the battery is fully charged or not, which saves power. 
         [0016]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram showing that a conventional adaptor supplies power to an electronic device. 
           [0018]      FIG. 2  is a schematic diagram showing that a charger of a conventional adaptor charges a battery. 
           [0019]      FIG. 3  is a schematic diagram showing that an adaptor is applied to an electronic device without a battery installed in an embodiment of the invention. 
           [0020]      FIG. 4  a schematic diagram showing that an adaptor is applied to an electronic device with a battery installed in an embodiment of the invention. 
           [0021]      FIG. 5  is a chart showing control signals Va outputted by a state generator and corresponding voltages DC_in outputted by an adaptor when an electronic device operates at different states in an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0022]    The electronic device further includes a state generator. The state generator adjusts the power supplied to an electronic device according to whether the electronic device has a battery, an operation state of the electronic device and whether the battery is fully charged or not, which saves power. 
         [0023]      FIG. 3  is a schematic diagram showing that an adaptor is applied to an electronic device without a battery installed. An electronic device  30  includes a host  302  and a state generator  34 . An input end of the adaptor  32  is connected to an input AC AC_in, and an output end of the adaptor  32  is connected to the electronic device  30  to supply a DC voltage DC_in to the electronic device  30 . Furthermore, the adaptor  32  includes a state receiving terminal SS for receiving a control signal Va. According to an embodiment of the invention, the state generator  34  outputs the control signal Va to the state receiving terminal SS of the adaptor according to the operation state of the host  302 , and the adaptor  32  adjusts the DC voltage DC_in supplied to the host  302  according to the received control signal Va. 
         [0024]    For example, when the state generator  34  detects that the host  302  is at a SO state (such a power off state), since the electronic device  30  is not configured with a battery, it does not need to supply power to the battery. The state generator  34  outputs the control signal Va (which equals to V 0 ) to the state receiving terminal SS of the adaptor  32  to cut the power of the adaptor  32  off, which means that the DC voltage DC_in supplied by the adaptor  32  to the electronic device  30  is 0V. Thus, when the electronic device  30  is not configured with the battery and the host  302  is at the S 0  state (such as the power off state S 0 ), the power of the adaptor  32  is cut off completely, and the adaptor  32  consumes no power at the moment. 
         [0025]    Moreover, when the state generator  34  detects that the host  302  operates at a S 1  state (such as a hibernation state), the state generator  34  outputs the control signal Va (which equals to V 1 ) to the state receiving terminal SS of the adaptor  32  to make the DC voltage (DC_in) outputted by the adaptor  32  to the electronic device  30  be the first voltage DC 1 . The first voltage DC 1  is the minimum voltage needed by the electronic device  30  when it operates at the S 1  state (such as the hibernation state). Consequently, the adaptor  32  saves power. 
         [0026]    Similarly, when the state generator  34  detects that the host  302  operates at other states (S 2  to Sn, such as a standby state, a sleep state, and an operation state), the state generator  34  outputs the corresponding control signal Va (which is one of V 2  to Vn) to the state receiving terminal SS of the adaptor  32  to make the DC voltage DC_in outputted by the adaptor  32  to the electronic device  30  be the corresponding voltage DC 2  to DCn. Thus, the adaptor  32  generates the corresponding voltage to the electronic device according to the state of the host  302  of the electronic device  30 , and the power saving function of the adaptor  32  is achieved. 
         [0027]      FIG. 4  a schematic diagram showing that an adaptor is applied to an electronic device with a battery installed. When the state generator  34  detects that the electronic device  30  is configured with a battery, and the state generator  34  detects that the electronic device  30  operates at the battery state Sb, the state generator  34  outputs the control signal Va (which equals to Vb) to the state receiving terminal SS of the adaptor  32  to make the DC voltage DC_in outputted to the electronic device by the adaptor  32  be a charging voltage DC_IN (which equals to DC). Generally, the charging voltage DC is the maximum voltage outputted by the adaptor  32  to make the battery  304  fully charged under the charging voltage DC in the shortest time. 
         [0028]    Once the battery  304  is fully charged, the state generator  34  acts according to the other state signals S 0  to Sn outputted by the host  302 . For example, when the electronic device  30  is at the power off state, but the battery  304  is not fully charged, the host  302  outputs the battery state Sb, the state generator  34  outputs the control signal Va (which equals to Vb) to allow the adaptor  32  to output the maximum voltage DC. When the battery  304  is fully charged, the host  302  outputs the SO state (such as the power off state) immediately, and the state generator  34  outputs the shutdown control signal Va (which equals to V 0 ) to the adaptor  32  to cut the power of the adaptor  32  off completely, and that is, the adaptor  32  does not supply power to the electronic device  30  (DC_in is 0V) at the moment. 
         [0029]      FIG. 5  is a chart showing that control signals Va outputted by a state generator and corresponding voltages DC_in outputted by an adaptor when an electronic device operates at different states. As shown in  FIG. 5 , when the host  302  operates at different states, the host  302  generates different state signals (S 0  to Sn, or Sb) to the state generator  34  to allow the state generator  34  to output the control signal Va to the state receiving terminal SS of the adaptor  32 . The adaptor  32  outputs the corresponding output DC voltage DC_in to the electronic device  30  according to the control signal Va. 
         [0030]    In sum, in the embodiment, the adaptor adjusts the voltage supplied to the electronic device according to whether the electronic device has a battery, the operation state of the electronic device, and whether the battery is fully charged or not, which saves power. 
         [0031]    Furthermore, in the embodiment, the electronic device operates at the power off state, the hibernation state or the sleep state, which is not for limiting the invention, the adaptor may also be applied to the electronic device operating at other states. 
         [0032]    In the embodiment, the adaptor is applied to an electronic device such as, but not limited to, a notebook computer, a mobile phone or a digital camera. It may also be applied to a charger, and the operating principle is the same as that of the adaptor applied to the electronic device, which is omitted herein. 
         [0033]    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. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments described above.
A power system includes an electronic device having a host and a state generator and an adaptor. The host is capable of presenting a plurality of states and generating a plurality of state signals corresponding to the states, and the state generator is electrically connected to the host, receives the state signals and generates a control signal accordingly. The adaptor is connected to an AC voltage and has a state receiving terminal to receive the control signal. The adaptor is capable of generating a DC voltage to the electronic device according to the control signal.