Abstract:
An electronic device, comprising a USB connector through which another electronic device is connected to the electronic device; and a power supply circuit that supplies power from a power source to the other electronic device via a specified pin other than a power supply pin of the USB connector.

Description:
INCORPORATION BY REFERENCE 
       [0001]    The disclosure of the following-priority application is herein incorporated by reference:
   Japanese Patent Application No. 2006-328228 filed Dec. 5, 2006   
 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to an electronic device connected through a USB (universal serial bus) interface. 
         [0005]    2. Description of Related Art 
         [0006]    The USB is known widely as an interface through which a personal computer and its peripheral devices are connected. A first device equipped with a USB host controller and a second device equipped with a USB device controller are typically connected through the USB interface. While the power is normally supplied from the first device to the second device via the USB connection, there are technologies known in the related art that allow power to be supplied from the second device to the first device as well (see, for instance, Japanese Laid Open Patent Publication No. 2005-25405). 
       SUMMARY OF THE INVENTION 
       [0007]    In a USB system adopting a technology in the related art that allows power to be supplied from the second device functioning as a USB device to the first device functioning as a USB host, the power supply is carried out via a supply line at the USB interface. This gives rise to a concern that if the first device has a power supply function as well, interference may occur with the power sources of both devices connected to the supply line. 
         [0008]    An electronic device according to the present invention comprises: a USB connector through which another electronic device is connected to the electronic device; and a power supply circuit that supplies power from a power source to the other electronic device via a specified pin other than a power supply pin of the USB connector. 
         [0009]    An electronic device according to another invention comprises: a USB device controller; a USB connector through which an electronic device equipped with a USB host controller is connected to the electronic device; and a power supply circuit that supplies power from a power source to the electronic device equipped with the USB host controller via a specified pin other than a power supply pin of the USB connector. 
         [0010]    In the electronic device according to the another invention, the specified pin is an identifier pin of the USB connector and the power supply circuit supplies power to the electronic device equipped with the USB host controller via the identifier pin. It is preferred that the power supply circuit includes a switching device that connects the power source with the identifier pin and disconnects the power supply from the identifier pin. 
         [0011]    A control unit that issues a switch instruction to the switching device can control the switching device to connect the power source with the identifier pin and disconnect the power supply from the identifier pin. The electronic device further comprises: an operation member that enables a menu operation to be performed to select a use/nonuse setting for the electronic device equipped with the USB host controller connected via the USB connector. The control unit issues the switch instruction to the switching device once use of the electronic device equipped with the USB host controller is allowed through the menu operation performed via the operation member. 
         [0012]    An electronic device according to yet another invention comprises: a USB host controller; a USB connector through which an electronic device equipped with a USB device controller is connected to the electronic device; and a power supply circuit to which power is supplied from the electronic device equipped with the USB device controller via a specified pin other than a power supply pin of the USB connector. 
         [0013]    In the electronic device according to the yet another invention, the specified pin is an identifier pin of the USB connector; and power is supplied to the power supply circuit via the identifier pin. The identifier pin and the power supply pin are connected with each other. 
         [0014]    In the electronic device according to the yet another invention, the power supply circuit includes a voltage converter that lowers or boosts a voltage supplied via the identifier pin and the voltage resulting from conversion at the voltage converter is applied to the power supply pin. 
         [0015]    An interface system according to the present invention comprises a first electronic device and a second electronic device. The first electronic device comprises a USB device controller; a USB connector through which the second electronic device equipped with a USB host controller is connected to the first electronic device; and a power supply circuit that supplies power from a power source to the second electronic device equipped with the USB host controller via a specified pin other than a power supply pin of the USB connector. The second electronic device comprises a USB host controller; a USB connector through which the first electronic device is connected to the second electronic device; and a power supply circuit that supplies power from the first electronic device equipped with the USB device controller via a specified pin other than a power supply pin of the USB connector. The first electronic device can be an electronic camera, equipped with blocks engaged in photographing processing such as an imaging optical system, an imaging sensor that captures an image of a subject, an image processing unit that executes image processing on an imaging signal output from the imaging sensor, a memory, an operation member and a recording medium; and the second electronic device can be a wireless LAN module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  illustrates the interface system achieved in a first embodiment of the present invention; 
           [0017]      FIG. 2  shows a USB device and a USB host that supplies power to the USB device, connected with each other via a USB cable; and 
           [0018]      FIG. 3  shows the USB host achieved in a second embodiment. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  illustrates the interface system achieved in the first embodiment of the present invention. The interface system shown in  FIG. 1  includes a plurality of electronic devices each equipped with a USB connector in compliance with the USB (universal serial bus) specification which is set forth by the USB Implementers Forum (USB-IF). In the embodiment, a USB device  10  and a USB host  50  are directly connected with each other through the USB connectors without using a cable and power is supplied from the USB device  10  to the USB host  50 . 
         [0020]    The USB device  10  may be, for instance, an electronic camera, whereas the USB host  50  may be a wireless LAN module. By directly connecting the wireless LAN module  50  to the electronic camera  10  via the USB connectors, image data accumulated in the electronic camera  10  can be directly transferred to a server or the like on a network without having to transmit the image data via a personal computer or the like. 
         [0021]    A USB connector comprises a power source VBUS line, a data D+ line and a data D− line, a reference potential GND line and an ID line. The ID line is used to identify a dual role device as a “USB host” or a “USB device”. A dual role device is a device that operates in compliance with the USB-OTG specification (On-The-Go Supplement to the USB 2.0 Specification) and may be determined to be operating as a “USB host” or as a “USB device” depending upon the voltage level detected in the ID line. 
         [0022]    Power supply between devices connected through a USB connection is normally executed through the VBUS line. In addition, the devices connected through the USB connection communicate with each other through serial communication via a pair of data lines, i.e. the D+ line and the D− line. 
         [0023]    The USB device  10  in  FIG. 1  includes a control unit  12 , a device controller  13 , a transistor  14 , a resistor  15 , a diode  16  and a connector RC  11 , with a battery  11  loaded therein. It is to be noted that an explanation of the structural blocks in the USB device  10  engaged in photographing processing executed in the camera (the imaging optical system, the imaging sensor, the image processing unit, the memory, the operation member, the recording medium and the like) is not provided in this specification. 
         [0024]    Power is supplied from the battery  11  to the various blocks constituting the USB device  10 , such as the control unit  12  and the device controller  13 . The control unit  12  includes a microcomputer and controls the operations of the various blocks in the USB device  10  (an electronic camera in this example). In response to an instruction from the control unit  12 , the device controller  13  executes control so as to enable the USB device  10  to operate as the “USB device”. Data communication between the USB device  10  and the USB host  50  is controlled by a host controller  51  to be detailed later. The USB device  10  cannot transmit data to the USB host  50  unless the USB host  50  grants a bus utilization authorization to the USB device  10 . 
         [0025]    The ON/OFF state of the transistor  14  is controlled in response to an instruction from the control unit  12 . As the transistor  14  enters an ON state, the power from the battery  11  is supplied to an ID pin of the connector RC  11  via the transistor  14  and the diode  16 . A switching element such as an analogue switch or a relay may be used in place of the transistor  14 . The diode  16  is disposed for purposes of preventing a reverse current flow. The resistor  15  is provided so as to set the potential at the base terminal of the transistor  14  to a predetermined level. 
         [0026]    The USB connectors used in the embodiment include the connector RC  11  at the USB device  10  and a connector PL  21  at the USB host  50 . The connector RC  11  is a mini B-type receptacle (mini-B receptacle). A mini B-type receptacle is a connector dedicated to the “USB device”. A mini B-type plug (mini-B plug) at the “USB host” or a “USB cable” can be plugged into the connector RC  11 . In the embodiment, the mini B-type plug (mini-B plug) at the USB host is connected to the connector RC  11 . The connector RC  11  includes a VBUS pin corresponding to the VBUS line, a D+ pin corresponding to the D+ line, a D− pin corresponding to the D− line, a GND pin corresponding to the GND line and the ID pin corresponding to the ID line. 
         [0027]    The USB host  50  includes a control unit  52 , the host controller  51  and the connector PL  21 . It is to be noted that the figure does not include an illustration of the blocks engaged in wireless communication processing in the USB host  50 . The USB host  50  does not have a power source and instead, it receives power supplied from the USB device  10  and delivers it to the host controller  51  and the control unit  52 . 
         [0028]    The control unit  52  includes a microcomputer and controls the operations of the various blocks in the USB host  50  (a wireless LAN module in this example). In response to an instruction from the control unit  52 , the host controller  51  executes control so as to enable the USB host  50  to operate as the “USB host”. Any processing via the bus is invariably triggered by the USB host  50  under control executed by the host controller  51 . 
         [0029]    The connector PL  21  is a mini B-type plug (mini-B plug) A mini B-type plug is a connector dedicated to the “USB host”. The mini B-type receptacle (mini-B receptacle) at the “USB device” i.e., the connector RC  11  is connected to the connector PL  21 . The connector PL  21  includes a VBUS pin corresponding to the VBUS line, a D+ pin corresponding to the D+ line, a D− pin corresponding to the D− line, a GND pin corresponding to the GND line and an ID pin corresponding to the ID line. It is to be noted that the VBUS pin and the ID pin-are connected with each other within the USB host  50 . 
         [0030]    The USB device  10  and the USB host  50  described above are utilized through the following procedure. 
         [0031]    (Procedural step 1) The USB device  10  and the USB host  50  become connected with each other via the connector RC  11  and the connector PL  21 . 
         [0032]    (Procedural step 2) At the USB device  10 , a wireless LAN module use/nonuse setting is selected through, for instance, a menu operation performed by using the operation member. As the use of the wireless LAN module becomes allowed, the control unit  12  at the USB device  10  turns on the transistor  14  by setting the base terminal at the transistor  14  to L level. As a result, power from the battery  11  is supplied from the USB device  10  to the USB host  50  through the ID line. 
         [0033]    If the wireless LAN module use setting is not selected, i.e., if the use of the wireless LAN module is not allowed, the control unit  12  at the USB device  10  sets the base terminal at the transistor  14  to H level, thereby turning off the transistor  14 . In this situation, the USB device  10  does not supply the power from the battery  11  to the USB host  50 . 
         [0034]    The following advantages are achieved in the first embodiment described above.
   (1) Since the power supply from the USB device  10  to the USB host  50  can be switched on/off, the power supply can be stopped on demand.   (2) Power can be supplied from the USB device  10  to the USB host  50  without having to constitute the USB device  10  as a dual role device, i e., without having to install a controller or software in compliance with the USB-OTG specification (USB On-The-Go Supplement to the USB 2.0 Specification) standard in the USB device. As a result, an inexpensive interface system is realized.   (3) Even if a USB cable in compliance with the USB-OTG is connected to the connector RC  11  of the USB device  10 , the power output from the ID pin of the USB device  10  is never short-circuited through the USB cable. At the standard USB cable in compliance with the USB-OTG, the ID pin of the mini-B plug to the “USB device” is open-circuited (unconnected) and the ID pin of the mini-A plug to the “USB host” is short-circuited (connected) with the GND pin. Accordingly, when the mini-B plug of the USB cable in compliance with the USB-OTG is connected with the connector RC  11  (mini-B receptacle) of the USB device  10 , the power output through the ID pin of the connector RC  11  is never shorted through the USB cable, assuring a safety.   
 
         [0038]      FIG. 2  illustrates another connection example.  FIG. 2  shows a USB device  10  and a USB host  60  connected with each other via a USB cable  65 . The USB host  60  in  FIG. 2  has a function of supplying power to a “USB device”. 
         [0039]    Since the USB device  10  is similar to that shown in  FIG. 1 , its explanation is omitted. It is to be noted that  FIG. 2  does not provide an illustration of the blocks engaged in the photographing processing executed in the camera. The USB cable  65  is a directional cable. A connector PL  42  disposed at one end of the USB cable  65  is a mini B-type plug (mini-B plug). The mini B-type plug is a connector to the “USB device”. The mini B-type receptacle (mini-B receptacle) of the “USB device”, i.e., the connector RC  11 , is connected to the connector PL  42 . 
         [0040]    A connector PL  41 , disposed at the other end of the USB cable  65 , is an A-type plug (A plug). The A-type plug is a connector to the “USB host”. An A-type receptacle (A receptacle) of the “USB host”, i.e., a connector RC  31 , is connected to the connector PL  41 . Since the connectors disposed at the two ends of the USB cable  65  assume different shapes, two “USB hosts” or two “USB devices” are never connected with each other by mistake. 
         [0041]    The connector PL  41  is a full-size connector with four pins. The connector PL  42  is a mini-type connector such as that explained earlier and includes five pins. Since the connector PL  41  does not include an ID pin, the USB cable  65  does not include a wiring for ID pin connection and the ID pin of the connector PL  42  is left open-circuited (unconnected). 
         [0042]    The USB host  60  includes a control unit  62 , a host controller  61  and the connector RC  31  (A-type receptacle), with a battery  63  loaded therein. It is to be noted that an illustration of the structural blocks in the USB host  60  engaged in wireless communication processing is not provided. The USB host  60  supplies power from the battery  63  to the host controller  61  and the control unit  62 . 
         [0043]    The control unit  62  includes a microcomputer and controls the operations of the various blocks in the USB host  60  (a wireless LAN module in this example). In response to an instruction from the control unit  62 , the host controller  61  executes control so as to enable the USB host  60  to operate as the “USB host”. Any processing via the bus is invariably triggered by the USB host  60  under control executed by the host controller  61 . 
         [0044]    The connector RC  31  is an A-type receptacle (A receptacle). An A receptacle is a connector dedicated to the “USB host”. The connector PL  41  (A plug) of the USB cable  65  is connected to the connector RC  31 . The connector RC  31  includes a VBUS pin corresponding to the VBUS line, a D+ pin corresponding to the D+ line, a D− pin corresponding to the D− line and a GND pin corresponding to the GND line. It is to be noted that the VBUS terminal is connected with the power line (the positive pole side of the battery  63 ) within the USB host  60 . 
         [0045]    The structure shown in  FIG. 2  allows the USB device  10  to judge whether or not the USB host  60  is connected to the USB device  10  simply by checking the voltage at the VBUS pin. In addition, the USB device  10  is able to engage in operation on the power provided therein (from the battery  11 ) without having to rely on power supplied from the “USB host” via the VBUS line. 
         [0046]      FIG. 3  shows a USB host  70  achieved in the second embodiment. The USB host  70  includes a control unit  72 , a host controller  71 , a voltage converter  73  and a connector PL  21 . It is to be noted that the figure does not include an illustration of the blocks engaged in wireless communication processing in the USB host  70 . The USB host  70  receives power supplied from the USB device  10  and then delivers the power thus received to the host controller  71  and the control unit  72 . 
         [0047]    The control unit  72  includes a microcomputer and controls the operations of the various blocks in the USB host  70  (a wireless LAN module in this example). In response to an instruction from the control unit  72 , the host controller  71  executes control so as to enable the USB host  70  to operate as the “USB host”. Any processing via the bus is invariably triggered by the USB host  70  under control executed by the host controller  71 . 
         [0048]    The connector PL  21  (mini-B plug) is identical to the connector assigned with the same reference numeral in  FIG. 1  and, accordingly, its explanation is omitted. The voltage converter  73  converts the voltage (e.g., DC 12 V) received via the ID terminal of the connector PL  21  to a voltage at a predetermined level (e.g., DC 5V), and supplies the voltage resulting from the conversion to the VBUS pin of the connector PL  21 . The voltage converter  73  may be constituted with, for instance, a voltage regulator, a transformer, a DC/DC converter or the like. 
         [0049]    In the second embodiment described above, the USB host  70  includes the voltage converter  73  so as to first convert the voltage received from the USB device  10  and then supply the voltage resulting from the conversion to the VBUS pin of the USB device  10 . This structure allows the present invention to be adopted even when the USB device  10  and the USB host  70  operate on different voltages. 
         [0050]    While the voltage is lowered via the converter  73  in the example explained above, the voltage may instead be boosted via the voltage converter for the adoption of the present invention. 
         [0051]    The present invention may be adopted in a structure that includes a voltage converter through which the voltage to be supplied to the host controller  71  (or the control unit  72 ) is converted. 
         [0052]    While an explanation is given above on an example in which the USB device  10  is constituted with an electronic camera, the present invention is not limited to this example and it may be adopted in conjunction with a USB device constituted with a portable electronic device such as a portable telephone or a PDA. 
         [0053]    While the USB host  50  in the description provided above is a wireless LAN module, the present invention may be adopted in conjunction with a USB host constituted with a tuner module, a GPS reception unit module or the like, instead. 
         [0054]    The above described embodiments are examples, and various modifications can be made without departing from the scope of the invention.