Abstract:
A terminal for a power supply system is disclosed. The terminal may have a connection portion, a battery that receives power from an external device via the connection portion, and a detector that detects a data signal from the external device. The terminal may also have a determination unit, a current converter that selectively converts an amount of charging current from a first current to a second current larger than the first current, and a controller that controls charging of the battery on the basis of a determination result. The controller is configured to control the current converter to charge the battery with the first current when the determination unit determines the external device is not a dedicated power supply, and to control the current converter to charge the battery with the second current when the determination unit determines the external device is a dedicated power supply.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention contains subject matter related to Japanese Patent Application JP 2005-251543 filed in the Japanese Patent Office on Aug. 31, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to dedicated power supply apparatuses, terminals, power supply systems, and power supply methods, and in particular, to a power supply technique applicable to mobile devices that can be carried around. 
     2. Description of the Related Art 
     A rapidly increasing number of mobile devices, such as digital audio players, that are small and can be carried around are being widely used. Many of these mobile devices are capable of performing high-speed data communication with computers by establishing universal serial bus (USB) connections. There are various methods for charging a battery in such a mobile device. For example, one method uses an alternating current (AC) jack for power supply, another method uses a cradle, and yet another method uses a USB. When a mobile device is provided with a USB terminal for data communication and an AC jack for power supply, the device becomes larger in size and is thus not attractive in appearance, and wiring connections become complicated. There are some mobile devices that are provided with cradles serving as dedicated chargers for holding and charging the mobile devices. Because it is necessary to have such large cradles at all times, it is difficult to make full use of the convenience of small mobile devices. 
     In view of the above-described points, it is preferable that USB-connectable mobile devices be charged by establishing USB connections. When charging is done by establishing USB connections, mobile devices can be charged by simply connecting them to computers. Therefore, many mobile devices that can be charged by establishing USB connections are not provided with an AC jack for power supply but are provided with only a USB jack for data communication and charging in order to reduce the size of the mobile devices, to not ruin the appearance of the mobile devices, and to enhance the simplicity of wiring connections. 
     In the case of mobile devices that are not provided with AC jacks for power supply, it is difficult to charge such a mobile device when there is no computer. In normal usage, such a mobile device is convenient since it can be charged by connecting it via USB to a computer. However, if a user of such a mobile device is on a trip and has no computer on hand, it is difficult to charge such a mobile device. In order to prevent this problem, adapters that can be connected to a home power supply, convert this power to predetermined power, and supply the predetermined power to mobile devices by establishing USB connections have been developed. Such adapters are referred to as “USB adapters” (for example, see Japanese Unexamined Patent Application Publication No. 2005-6497). 
     SUMMARY OF THE INVENTION 
     Known USB adapters described above employ a standard four-pin USB connector provided with a total of four terminals. The four terminals include a +5 power supply terminal for power supply, a ground terminal, a D+ terminal for data transmission, and a D− terminal for data transmission. According to the power supply specification of such USB adapters, an output voltage of 5 V±0.25 V and an output current of 500 mA are necessary, and the power supply terminal is designed to satisfy the specification. In contrast, the D+ and D− terminals for data transmission are open, and nothing has been done in this regard. Thus, the operation of the D+ and D− terminals is unstable. 
     When establishing a connection between a mobile device and a USB adapter, it is necessary for the mobile device not to mistakenly recognize that the USB adapter has been suspended. When the mobile device mistakenly recognizes that the USB adapter has been suspended, the mobile device can only receive power of 500 μA or less from the USB adapter. In known USB adapters, however, nothing has been done for the D+ and D− terminals for data transmission, and hence the mobile device may mistakenly recognize that the USB adapter has been suspended. 
     In view of the above-described problems, it is desirable to provide a dedicated power supply apparatus, a terminal, a power supply system, and a power supply method capable of providing a safe charging system and suppressing malfunction or unstable operation of the terminal while the dedicated power supply apparatus is being connected. 
     According to an embodiment of the present invention, there is provided a dedicated power supply apparatus for supplying power to a rechargeable power source or the like in a mobile device. The dedicated power supply apparatus includes a regulator that receives power from an external power source, two signal lines to which the regulator is connected, and two resistors, each placed between the regulator and an associated one of the signal lines. 
     With this structure, the two signal lines can be pulled up to a predetermined voltage by placing each of the two resistors between the regulator and an associated one of the two signal lines. Accordingly, a device connected to the dedicated power supply apparatus is prevented from mistakenly recognizing that the dedicated power supply apparatus has been suspended, and this device is thereby prevented from being suspended. Thus, malfunction or unstable operation of the device can be suppressed, and a safe charging system can be provided. 
     Each of the two resistors may not necessarily be placed between the regulator and an associated one of the two signal lines. For example, there are some cases where a resistor is placed between the regulator and at least one of the signal lines. That is, there are two types of USB devices. One is low-speed devices, such as a mouse, and the other is full-speed devices, such as a hard disk. By connecting the two resistors to the associated two signal lines, both types of USB devices can be handled. In order to handle only one type of USB device, such as low-speed devices or full-speed devices, a resistor may be connected to only one signal line. This point will be described subsequently. 
     According to another embodiment of the present invention, there is provided a terminal including a rechargeable power source or the like and receiving power from an external device. The terminal includes a connection portion to be connected to an external device, a battery that receives power from the external device via the connection portion, a detector that detects a data signal from the external device when the connection portion is connected to the external device, a determination unit that determines whether the external device is a dedicated power supply apparatus on the basis of a detection result obtained by the detector, and a controller that controls charging of the battery on the basis of a determination result obtained by the determination unit. 
     The data signal from the external device may be a signal indicating that the external device performs data communication. 
     The terminal may further include a current converter that converts, on the basis of determination performed by the determination unit, the amount of charging current from a first current prior to the determination to a second current larger than the first current. 
     The terminal can perform appropriate charging by determining whether a connection destination at the time of charging is a computer or a dedicated power supply apparatus such as a USB adapter. With this structure, the terminal determines whether a signal, such as start of frame (SOF), indicating that data transmission is performed is transmitted. When the terminal determines that the connection destination is a dedicated power supply apparatus, the terminal can perform appropriate charging. 
     According to a further embodiment of the present invention, there is provided a terminal including a connection portion to be connected to an external device, a battery that receives power from the external device via the connection portion, a detector that detects whether signal lines included in the connector are maintained at predetermined logical states, such as logical high states, a determination unit that determines whether the external device is a dedicated power supply apparatus on the basis of a detection result obtained by the detector, and a controller that controls charging of the battery on the basis of a determination result obtained by the determination unit. 
     With this structure, appropriate charging can be performed when it is determined, by determining the logical states of the two signal lines, that the communication destination is a dedicated power supply apparatus. For example, appropriate charging can be performed when it is determined, by determining whether both the signal lines are maintained at logical high states, that the communication destination is a dedicated power supply apparatus. 
     The terminal may further include a current converter that converts, on the basis of determination performed by the determination unit, the amount of charging current from a first current prior to the determination to a second current larger than the first current. The first and second currents are, for example, 100 mA and 500 mA, respectively. With this structure, the amount of current can be increased subsequent to determining that the communication destination is a dedicated power supply apparatus. For example, the amount of current can be increased from 100 mA to 500 mA. 
     According to still a further embodiment of the present invention, there is provided a power supply system including a dedicated power supply apparatus and a terminal, to which power is supplied from the dedicated power supply apparatus. The dedicated power supply apparatus includes a regulator that receives power from an external power source, two signal lines to which the regulator is connected, and two resistors, each placed between the regulator and an associated one of the two signal lines. The terminal includes a connection portion to be connected to an external device, a battery that receives power from the external device via the connection portion, a detector that detects data from the external device when the connection portion is connected to the external device, a determination unit that determines whether the external device is the dedicated power supply apparatus on the basis of a detection result obtained by the detector, and a controller that controls charging of the battery on the basis of a determination result obtained by the determination unit. 
     With this system, in the dedicated power supply apparatus, the two signal lines can be pulled up to a predetermined voltage by placing each of the two resistors between the regulator and an associated one of the two signal lines. Accordingly, a device connected to the dedicated power supply apparatus is prevented from being suspended. The terminal determines whether a signal, such as SOF, indicating that data transmission is performed is transmitted. On the basis of the determination result, the terminal determines whether the connection destination device is the dedicated power supply apparatus, such as a USB adapter. Accordingly, the terminal can perform appropriate charging. In this manner, malfunction or unstable operation of the terminal can be suppressed, and a safe charging system can be provided. 
     According to yet another embodiment of the present invention, there is provided a power supply method for supplying power to a terminal. The power supply method includes the steps of: detecting whether an external device is connected; receiving power from a detected external device and starting charging; detecting a data signal from the external device after starting charging; and controlling the amount of power received from the external device on the basis of a result of detecting the data signal from the external device after starting charging. 
     With this method, after starting charging, the terminal detects a signal, such as SOF, indicating that the external device performs data transmission. On the basis of the detection result, the terminal controls charging. In this manner, malfunction or unstable operation of the terminal connected to a dedicated power supply apparatus can be suppressed, and a safe charging system can be provided. 
     According to the embodiments of the present invention, the dedicated power supply apparatus includes the two resistors, each placed between the regulator and an associated one of the two signal lines. Thus, the two signal lines can be pulled up to a predetermined voltage. Also, a device connected to the dedicated power supply apparatus is prevented from being suspended. The terminal determines whether a signal, such as SOF, indicating that data transmission is performed is transmitted. The terminal can perform appropriate charging when it is determined that the communication destination device is the dedicated power supply apparatus, such as a USB adapter. In this manner, malfunction or unstable operation of the terminal can be suppressed, and a safe charging system can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example of a connection state when a USB connection is established between a USB adapter and a device; 
         FIG. 2A  is a diagram of the overall structure of data to be transferred, including SOF; 
         FIG. 2B  is a diagram of the frame structure of data to be transferred, including SOF; 
         FIG. 2C  is a diagram of the transaction structure of data to be transferred; 
         FIG. 3  is a diagram of a verification method of verifying transitions to a suspended state; 
         FIG. 4  is a table of the verification results of verifying the transitions to the suspended state; 
         FIG. 5  is a diagram of a power supply system according to an embodiment of the present invention; 
         FIG. 6  is a flowchart of a first USB adapter detection method; 
         FIG. 7  is a flowchart of a second USB adapter detection method; 
         FIG. 8  is a flowchart of a third USB adapter detection method; 
         FIG. 9  is a diagram of a power supply system according to another embodiment of the present invention; and 
         FIG. 10  is a flowchart of another example of a USB adapter detection method. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the accompanying drawings, a dedicated power supply apparatus, a terminal, a power supply system, and a power supply method according to preferred embodiments of the present invention will be described in detail. In the specification and the drawings, elements that have substantially the same functions are denoted by the same reference numerals, and repeated descriptions thereof will be omitted. 
     According to an embodiment of the present invention, a dedicated power supply apparatus for charging a battery that is included in a device and can be recharged by establishing a USB connection (hereinafter referred to as a “USB adapter”) will be described. In this embodiment, the term “device” refers to a device that can receive power from a computer, which is a USB host, or from the USB adapter by establishing a connection via USB. The device in the embodiment mainly assumes a mobile device that can be carried around. However, the device is not limited to that suitable for being carried around and includes all terminals that can receive power from a USB-connection destination. 
     In this embodiment, it is desirable to prevent the device from being suspended while connected to the USB adapter. When the computer is suspended while the device is being connected to the computer, the device is also suspended. At this time, the device can only receive a current of about 500 μA, and it is difficult for the device to actually request the computer to supply power to the device. 
     When the device is connected to the USB adapter, it is not necessary to suspend the device. However, it is difficult for the device to determine whether a connection destination device is a USB device or a computer. Thus, the device may mistakenly recognize a state where the device is being connected to the USB adapter as a state where the device is being connected to the suspended computer. In this embodiment, it is desirable to prevent such erroneous recognition. 
       FIG. 1  is a diagram of an example of a power supply system. A USB adapter  110 , which is an example of the dedicated power supply apparatus, and a device  120 , which is an example of the terminal, are connected to each other via USB. The USB adapter  110  is connected via a power plug  118  to an external power source  140 .  FIG. 1  only shows elements that are necessary for the description below. 
     USB Adapter  110   
     The USB adapter  110  includes, as shown in  FIG. 1 , a regulator  111 , (a signal generator  112 ), and a USB connector  113 . The regulator  111  receives a voltage from the external power source  140  and converts the voltage to a voltage that can be used as a charging voltage. The external power source  140  supplies, for example, an AC voltage ranging from 100 V to 240 V for home power supply, and the regulator  111  converts this voltage to, for example, a DC voltage of 5 V. (The signal generator  112  generates a signal for data transmission. It is not necessary to provide the signal generator  112 .) 
     The USB connector  113  is a standard four-pin USB connector and includes a +5V terminal  114 , a GND terminal  115 , a D+ terminal  116 , and a D− terminal  117 . The +5V terminal  114  and the GND terminal  115  are power supply terminals to be connected to the regulator  111 . The D+ terminal  116  and the D− terminal  117  are data transmission terminals to be connected to the signal generator  112 . The D+ terminal  116  is grounded via, for example, a resistor R 12  of 15 kΩ. The D− terminal  117  is grounded via, for example, a resistor R 22  of 15 kΩ. 
     Device  120   
     The device  120  includes, as shown in  FIG. 1 , a USB port  121  and a battery  122 . The USB port  121  is a port to which the USB connector  113  of the USB adapter  110  is connected. The USB port  121  includes a Vusb terminal  123 , a GND terminal  124 , a D+ terminal  125 , and a D− terminal  126 . The battery  122  is a rechargeable power source and is, for example, a lithium-ion battery. 
     Upon connection of the device  120  to the USB adapter  110 , the Vusb terminal  123  is connected to the +5V terminal  114  of the USB adapter  110 , the GND terminal  124  is connected to the GND terminal  115  of the USB adapter  110 , the D+ terminal  125  is connected to the D+ terminal  116  of the USB adapter  110 , and the D− terminal  126  is connected to the D− terminal  117  of the USB adapter  110 . 
     The D+ terminal  125  is connected via, for example, a resistor  31  of 1.5 kΩ to a 3.3 V power source and is thereby pulled up. The device  120  shown in  FIG. 1  assumes a device, such as a hard disk, that performs full-speed communication. When the device  120  is a device, such as a mouse, that performs low-speed communication, the D− terminal  126  is to be pulled up. 
     The device  120  recognizes a connection with the USB adapter  110  when +5 V power is supplied from the +5V terminal  114  of the USB adapter  110  to the Vusb terminal  123 . In contrast, the USB adapter  110  recognizes a connection with the device  120  when the device  120  pulls up the D+ terminal  116  using the resistor  31 . 
     The case of transition to a suspended state of a device that establishes a USB connection, such as that shown in FIG.  1 , will be described. A device that establishes a USB connection, such as that shown in  FIG. 1 , determines whether a connection destination electronic device, such as a computer, has been suspended. If it is determined that the connection destination electronic device has been suspended, the device is also suspended. When the USB-connection destination is idle for 3 ms or longer and when no SOF or no other signals are sent from the USB-connection destination, the device  120  is suspended. The idle state is a state where, in the case of a low-speed device, the D+ terminal  125  is low and the D− terminal  126  is high, and, in the case of a full-speed device, the D+ terminal  125  is high and the D− terminal  126  is low. In this specification, the logical high state is simply expressed as “high”, and the logical low state is simply expressed as “low”. 
     The SOF will now be described.  FIGS. 2A to 2C  are diagrams of the structure of data to be transferred, including SOF. The actual data flowing on a USB line is communicated in units referred to as “frames”. A frame is repeatedly transferred with a 1 ms period, as shown in  FIG. 2A . All data is exchanged in frames. The frame structure includes, as shown in  FIG. 2B , a plurality of “transactions” starting with a “packet” referred to as a “start of frame (SOF)”. A packet is a minimum unit communicated in USB communication, and there are a few types of packets. When a few packets are communicated to form a unit of meaningful data transmission, this unit is referred to as a “transaction”. As shown in  FIG. 2C , there are three types of transactions including SETUP, OUT, and IN. The length of data to be transferred depends on the setting. 
     As has been described above, by preventing the USB adapter  110  from being idle while the device  120  is being USB-connected to the USB adapter  110 , it can be regarded that it is possible to prevent the device  120  from being suspended. As shown in  FIG. 3 , in a USB adapter  210 , it is assumed that resistors R 11  and R 12  of 15 kΩ are connected to a D+ terminal  211 , and resistors R 21  and R 22  of 15 kΩ are connected to a D− terminal  212 . The resistors R 11 , R 12 , R 21 , and R 22  are connected and disconnected to verify whether the device  220  becomes suspended. 
       FIG. 4  is a table of the results of verification performed in  FIG. 3 . Which resistors are connected to the D+ terminal  211  and the D− terminal  212  is determined by various viewpoints, such as preventing the USB adapter  210  from being suspended, preventing the D+ terminal  211  and the D− terminal  212  from presenting high impedance, and preventing unnecessary leakage current. In the states of the D+ terminal  211  and the D− terminal  212  indicated by rows A, B, C, D, and E of the table shown in  FIG. 4 , it is difficult to prevent the D+ terminal  211  and the D− terminal  212  from presenting high impedance. In the states of the D+ terminal  211  and the D− terminal  212  indicated by rows G, H, and I, the device  220  mistakenly recognizes that the USB adapter  210  is idle. It is thus difficult to prevent the device  220  from being suspended. For example, row H indicates the case where the D+ terminal  211  is low and the D− terminal  212  is high. In this case, the device  220  mistakenly determines that the connection destination USB adapter  210  is a low-speed device and is idle. However, in the states of the D+ terminal  211  and the D− terminal  212  indicated by row F, the D+ terminal  211  and the D− terminal  212  do not present high impedance, and the device  220  is not suspended. Therefore, it has been verified that it is optimal to connect the resistors R 11  and R 12  to the D+ terminal  211  and the D− terminal  212 , respectively, to pull up both the D+ terminal  211  and the D− terminal  212 . The pull-up voltage is, for example, 3.3 V. By pulling up both the D+ terminal  211  and the D− terminal  212 , the device  220  connected to the USB adapter  210  is prevented from being suspended. 
       FIG. 5  is a diagram of a power supply system according to an embodiment of the present invention and shows a USB connection between a USB adapter  310 , which is an example of the dedicated power supply apparatus, and a device  320 , which is an example of the terminal. The USB adapter  310  is connected via a power plug  319  to an external power source  340 .  FIG. 5  only shows elements that are necessary for the description below. 
     USB Adapter  310   
     The USB adapter  310  includes, as shown in  FIG. 5 , a regulator  311  and a USB connector  313 . The regulator  311  receives a voltage from the external power source  340  and converts the voltage to a voltage that can be used as a charging voltage. The external power source  340  supplies, for example, an AC voltage ranging from 100 V to 240 V for home power supply, and the regulator  311  converts this voltage to, for example, a DC voltage of 5 V. 
     The USB connector  313  is a standard four-pin USB connector and includes a +5V terminal  314 , a GND terminal  315 , a D+ terminal  316 , and a D− terminal  317 . The +5V terminal  314  and the GND terminal  315  are power supply terminals to be connected to the regulator  311 . The D+ terminal  316  and the D− terminal  317  are data transmission terminals, which will be described subsequently. 
     The USB adapter  310  shown in  FIG. 5  is different from the USB adapter  110  shown in  FIG. 1  in that, for example, the D+ terminal  316  is connected to a regulator  318  via, for example, the resistor R 11  of 15 kΩ, and the D− terminal  317  is connected to the regulator  318  via, for example, the resistor R 21  of 15 kΩ. The regulator  318  receives a voltage from the +5 terminal  314  and the GND terminal  315 , which are power supply terminals, and converts this voltage to, for example, 3.3 V. Thus, the D+ terminal  316  and the D− terminal  317 , which are data transmission terminals, can be pulled up to 3.3 V. The USB adapter  310  includes no signal generator  112  shown in  FIG. 1 , and the resistors R 11  and R 12  are connected to the D+ terminal  316  and the  317 , respectively. 
     In this embodiment, the case where the D+ terminal  316  and the D− terminal  317  are pulled up to 3.3 V is described by way of example. However, the present invention is not limited to this case. Alternatively, the D+ terminal  316  and the D− terminal  317  may be pulled up to an arbitrary voltage, such as 1.5 V or 15 V. 
     In this embodiment, the case where both the D+ terminal  316  and the D− terminal  317  are pulled up is described by way of example. However, the present invention is not limited to this case. Alternatively, a low-speed device can be handled by pulling up the D+ terminal  316  of the USB adapter  310 , and a full-speed device can be handled by pulling up the D− terminal  317  of the USB adapter  310 . At present, most USB devices are full-speed devices, and it is expected that this trend will continue in the future. In the case where a full-speed device is to be handled and no low-speed device is taken into consideration, only the D− terminal  317  of the USB adapter  310  may be pulled up. 
     As has been described above, according to the USB adapter  310  according to the embodiment, the D+ terminal  316  and the D− terminal  317  of the USB adapter  310  are pulled up. Thus, the device  320  is prevented from being suspended, which may be caused by the device  320  mistakenly recognizing that the USB adapter  310  has been suspended. 
     Next, the device will be described. The structure of the device  120  shown in  FIG. 1  does not enable the device  120  to determine whether the USB connection destination is a computer or a USB adapter. Basically, the USB standard does not allow the current supply to the device  120  to be increased from 100 mA to 500 mA unless permission is obtained from a computer serving as the connection destination. However, when the connection destination is a USB adapter, it is not necessary for the device  120  to obtain permission from the USB adapter. Thus, when it is necessary to quickly charge the device  120  by receiving a current of 500 mA, it is necessary for the device  120  to detect whether the USB connection destination is a USB adapter or a computer. Hereinafter, how this point can be accomplished will be described. 
     It is only necessary for the device  320  to determine whether the USB connection destination is a computer or a USB adapter. When the USB connection destination is a computer, the device  320  can receive a current of 500 mA after obtaining permission from the computer. When the USB connection destination is a USB adapter, the device  320  can receive a current of 500 mA without obtaining permission from the USB adapter. Hereinafter, the structure of the device based on this viewpoint will be described. 
     Device  320   
     The device  320  includes, as shown in  FIG. 5 , a USB port  321  and a battery  322 . The USB port  321  is a port to which the USB connector  313  of the USB adapter  310  is connected. The USB port  321  includes a Vusb terminal  323 , a GND terminal  324 , a D+ terminal  325 , and a D− terminal  326 . The battery  322  is a rechargeable power source and is, for example, a lithium-ion battery. 
     Upon connection of the device  320  to the USB adapter  310 , the Vusb terminal  323  is connected to the +5V terminal  314  of the USB adapter  310 , the GND terminal  324  is connected to the GND terminal  315  of the USB adapter  310 , the D+ terminal  325  is connected to the D+ terminal  316  of the USB adapter  310 , and the D− terminal  326  is connected to the D− terminal  317  of the USB adapter  310 . 
     The D+ terminal  325  is connected via, for example, the resistor  31  of 1.5 kΩ to the 3.3 V power source and is thereby pulled up. The device  320  shown in  FIG. 5  assumes a full-speed device, such as a hard disk. When the device  320  is a low-speed device, such as a mouse, the D− terminal  326  is to be pulled up. 
     The device  320  recognizes a connection with the USB adapter  310  when +5 V power is supplied from the +5V terminal  314  of the USB adapter  310  to the Vusb terminal  323 . In contrast, the USB adapter  310  recognizes a connection with the device  320  when the device  320  pulls up the D+ terminal  316  using the resistor  31 . 
     The device  320  shown in  FIG. 5  further includes a detector  327 , a determination unit  328 , a controller  329 , a playback controller  330 , a playback unit  331 , a storage medium  332 , and an operation unit  333 . The detector  327  is connected to the D+ terminal  325  and the D− terminal  326  for data transmission. When the USB port  321  is connected to an external device such as the USB adapter  310  or a computer, the detector  327  detects a signal indicating that the external device performs data transmission. The determination unit  328  is connected to the detector  327  and determines whether the external device is the USB adapter  310  on the basis of the detection result obtained by the detector  327 . 
     The controller  329  is connected to the determination unit  328 , the Vusb terminal  323  and the GND terminal  324  for power supply, and the battery  322 . The controller  329  controls the charging of the battery  322  on the basis of the determination result obtained by the determination unit  328 . 
     The playback controller  330  receives a command from the operation unit  333  and controls the playback unit  331 . The playback unit  331  plays back an audio file, such as an MP3 file, stored on the storage medium  332 . Also, the playback unit  331  may be capable of playing back, in addition to audio files, files including images, moving images, and text. An output unit  335  outputs the audio file or the like played back by the playback unit  331 . The output unit  335  may be placed inside or outside the device  320 . 
     The detector  327 , the determination unit  328 , the controller  329 , the playback controller  330 , and the playback unit  331  may be implemented as functions of a central processing unit (CPU)  334 . Each function of the CPU  334  mainly consumes power charged in the battery  322  when executing processing. 
     There are three methods of the detector  327  of the device  320  determining whether the USB connection destination is a computer or a USB adapter, which will be described subsequently. 
     (1) SOF Signal Detection 
     When a device connected via USB to the device is a computer, the computer sends SOF to the device once in every predetermined period of time. The predetermined period of time is, for example, 1 ms. In contrast, because the USB adapter will not be in a suspended mode, the USB adapter sends no SOF to the device. Thus, when no SOF is sent from the USB connection destination within the predetermined period of time or longer, the device can determine that the connection destination is a USB adapter. 
     The flow of USB adapter detection will now be described with reference to  FIG. 6 . The USB connection destination will be referred to as the “external device”, which is, for example, a USB adapter or a computer. 
     In step S 102 , the device  320  is connected to the external device. In step S 104 , the device  320  recognizes a connection with the external device when the external device supplies +5 power to the Vusb terminal  323 . In step S 106 , the device  320  starts charging at 100 mA. In step S 108 , the device  320  starts an SOF queue timer. In step S 110 , the device  320  determines whether SOF is detected within the predetermined period of time. 
     If no SOF was detected and time ran out in step S 110 , in step S 112 , the device  320  recognizes that the USB connection destination is a USB adapter and starts charging at 500 mA. In step S 114 , after starting charging at 500 mA, the device  320  again determines whether SOF is detected within the predetermined period of time. If SOF is detected, in step S 116 , the device  320  determines that there was a mistake in recognition of the USB connection destination, and the device  320  returns to charging at 100 mA. 
     If SOF is detected in step S 110 , in step S 118 , the device  320  recognizes that the USB connection destination is a computer. The device  320  stops the SOF timer upon reception of even one command from the computer. In step S 120 , the computer executes the “Chapter 9 Protocol” handling to recognize a terminal connected thereto. In step S 122 , the device  320  sets whether to receive a current of 100 mA or a current of 500 mA after obtaining permission from the computer. In step S 124 , the device  320  performs the normal USB processing. 
     (2) Signal Line D+/D− Logical State Detection 
     A second method of the detector  327  of the device  320  determining whether the USB connection destination is a computer or a USB adapter will now be described. 
     According to the second method, the detector  327  of the device  320 , which is connected to the D+ terminal  325  and the D− terminal  326  for data transmission, has a function of determining whether the signal lines D+ and D− are maintained at predetermined logical states. The remaining portions are the same as those shown in  FIG. 5 . 
     The flow of USB adapter detection will now be described with reference to  FIG. 7 . 
     In step S 202 , the device  320  is connected to the external device. In step S 204 , the device  320  recognizes a connection with the external device when the external device supplies +5 power to the Vusb terminal  323 . In step S 206 , the device  320  starts charging at 100 mA. 
     In step S 208 , the device  320  detects the states of the signal lines D+ and D− using the detector  327 . The device  320  determines whether the signal lines D+ and D− are maintained at high/high states on the basis of the detection result. 
     If it is determined in step S 208  that the signal lines D+ and D− are maintained at high/high states, in step S 210 , the device  320  recognizes that the USB connection destination is a USB adapter and starts charging at 500 mA. 
     In contrast, if it is determined in step S 208  that the signal lines D+ and D− are not maintained at high/high states, in step S 212 , the device  320  recognizes that the USB connection destination is a computer. The computer executes the “Chapter 9 Protocol” handling to recognize a terminal connected thereto. In step S 214 , the device  320  sets whether to receive a current of 100 mA or a current of 500 mA after obtaining permission from the computer. In step S 216 , the device  320  performs the normal USB processing. 
     (3) SOF Signal Detection and D+/D− Logical State Detection 
     A third method of the detector  327  of the device  320  determining whether the USB connection destination is a computer or a USB adapter will now be described. 
     According to the third method, the detector  327  of the device  320 , which is connected to the D+ terminal  325  and the D− terminal  326  for data transmission, has two functions. One is to detect an SOF signal, and the other is to determine whether the signal lines D+ and D− are maintained at predetermined logical states. The remaining portions are the same as those shown in  FIG. 5 . 
     The flow of USB adapter detection will now be described with reference to  FIG. 8 . 
     In step S 302 , the device  320  is connected to the external device. In step S 304 , the device  320  recognizes a connection with the external device when the external device supplies +5 power to the Vusb terminal  323 . In step S 306 , the device  320  starts charging at 100 mA. 
     In step S 308 , the device  320  starts the SOF queue timer. In step S 310 , the device  320  determines whether SOF is detected within the predetermined period of time. In addition, the device  320  detects the states of the signal lines D+ and D−and determines whether the signal lines D+ and D− are maintained at high/high states. 
     If it is determined in step S 310  that the signal lines D+ and D− are maintained at high/high states, in step S 312 , the device  320  recognizes that the USB connection destination is a USB adapter and starts charging at 500 mA. In step S 314 , after starting charging at 500 mA, the device  320  again determines whether SOF is detected within the predetermined period of time. If SOF is detected, in step S 316 , the device  320  determines that there was a mistake in recognition of the USB connection destination, and the device  320  returns to charging at 100 mA. 
     If SOF is detected in step S 310 , in step S 318 , the device  320  recognizes that the USB connection destination is a computer. The device  320  stops the SOF timer upon reception of even one command from the computer. In step S 320 , the computer executes the “Chapter 9 Protocol” handling to recognize a terminal connected thereto. In step S 322 , the device  320  sets whether to receive a current of 100 mA or a current of 500 mA after obtaining permission from the computer. In step S 324 , the device  320  performs the normal USB processing. 
     According to the third method, the device performs both the SOF signal detection and the D+/D− logical state detection. It thus becomes unnecessary for the device to continue detecting SOF until the time of the SOF timer runs out. In this manner, the period of time for determining whether the USB connection destination is a computer or a USB adapter can be reduced. 
     As has been described above, the device  320  according to this embodiment includes the detector  327 , the determination unit  328 , and the controller  329 . The device  320  can determine whether the USB connection destination is a computer or a USB adapter. Thus, even when it is necessary to quickly charge the device  320 , optimal charging can be performed. 
     The case where the device  320  mistakenly detects a USB adapter when any one of the methods according to this embodiment is used will now be described. When the device  320  mistakenly detects that the USB connection destination is a USB adapter, the device  320  changes the current limit from 100 mA to 500 mA. When the USB connection destination is capable of supplying a current of 500 mA or greater, no significant problems will be caused. For example, when the USB connection destination is a root hub, the root hub is capable of supplying a current of 500 mA or greater. However, when the USB connection destination is a bus-powered hub, the bus-powered hub is capable of only supplying a current of 100 mA. As long as power is supplied to the bus-powered hub, the bus-powered hub outputs SOF regardless of the host state. Thus, the device will not mistakenly detect a USB adapter. Even when the device mistakenly detects a USB adapter, no significant negative impact will be caused. 
     Although the dedicated power supply apparatus, the terminal, the power supply system, and the power supply method according to the preferred embodiment of the present invention have been described with reference to the accompanying drawings, the present invention is not limited thereto. It is anticipated by those skilled in the art that a variety of modifications or changes may be made without departing from the technical scope of the invention set forth in the appended claims, and these modifications or changes may also be embraced in the scope of the present invention. 
     For example, in the above-described embodiment, the USB adapter, which includes no signal generator but includes the D+ terminal  316  and the D− terminal  317  connected to the resistors R 11  and R 21 , has been described. However, the present invention is not limited thereto. For example, as shown in  FIG. 9 , a signal generator  312  for generating a signal for data transmission may be provided. 
     In “(3) SOS Signal Detection and Signal Line D+/D− Logical State Detection” in the above-described embodiment, the case where the SOS signal detection and the D+/D− logical state detection are performed in parallel with each other has been described. However, the present invention is not limited to this case. For example, a process shown in  FIG. 10  may be performed. 
     In the example shown in  FIG. 10 , steps S 302 , S 304 , S 306 , S 308 , S 312 , S 314 , S 316 , S 318 , S 320 , S 322 , and S 324  are such as those described above. Steps S 309  and S 311  will now be described. In step S 309 , the device  320  determines whether SOF is detected within the predetermined period of time. If SOF is detected, the device  320  determines that the USB connection destination is a computer. When no SOF was detected and time ran out, in step S 311 , the device  320  further detects the states of the signal lines D+ and D−and determines whether the logical states of the signal lines D+ and D− are maintained at high/high states. If the logical states of the signal lines D+ and D− are maintained at high/high states, the device  320  determines that the device connected thereto via USB is a USB adapter. If the logical states of the signal lines D+ and D− are not maintained at high/high states, the device  320  determines that the device connected thereto via USB is a computer. 
     The SOF detection in step S 309  and the high/high state detection in step S 311  may be performed in the opposite order. Also, the series of processes may be performed by hardware by implementing the functional blocks shown in  FIGS. 5 and 9  using hardware. 
     Accordingly, the present invention can be employed in a dedicated power supply apparatus, a terminal, a power supply system, and a power supply method. In particular, the present invention can be employed in a dedicated power supply apparatus, a terminal, a power supply system, and a power supply method applicable to a mobile device that can be carried around, such as an audio player, a mobile phone, a digital camera, a camcorder, a portable game console, or a notebook computer. Also, the present invention is applicable to a dedicated power supply apparatus, a terminal, a power supply system, and a power supply method using not only a USB connector but also any type of connector for both data transmission and power supply.