Abstract:
A USB apparatus or a USB hub apparatus having a USB port to be used for transmitting and receiving information to and from a host computer according to the USB protocol is provided with a power supplying means for supplying power to each internal section of the USB apparatus or the USB hub apparatus, a power supply voltage detecting means for detecting presence/absence of a power supply voltage to be supplied from the host computer to the USB port, and a supply power control means for controlling the power that is supplied by the power supplying means in accordance with a detection result of the power supply voltage detecting means. The power supply voltage detecting means detects a power supply voltage that is supplied from the host computer to the USB port and informs the supply power control means of the detection result. The supply power control means causes the power supplying means to stop supplying power to each internal section of the USB apparatus or the USB hub apparatus if no power is supplied from the host computer to the USB port (i.e., the power of the host computer is off), and controls the power supplying means to have it supply ordinary power to each internal section of the USB apparatus or the USB hub apparatus if power is supplied from the host computer to the USB apparatus or the USB hub apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a USB apparatus and a USB hub apparatus. In particular, the invention relates to a USB apparatus which is connected to a host computer and transmits and receives information to and from it according to a protocol that complies with the USB standard, as well as to a USB hub apparatus which interconnects a host computer and one or more USB apparatuses and allows transmission and reception of information to be performed between them according to a protocol that complies with the USB standard. 
     2. Description of the Prior Art 
     In recent years, the reduction in the power consumption of electronic equipment has been promoted as part of various measures against the earth warming problem. 
     For example, personal computers or the like are constructed in such a manner that if a state that input devices (e.g., a keyboard, a mouse, etc.) are not manipulated has continued for a predetermined time or more, the personal computer automatically detects its unused state and renders a CRT (cathode-ray tube) monitor, for example, in a sleep mode to thereby reduce the power consumption. 
     Incidentally, in recent years, the USB (universal serial bus) has come into being as an interface for easily connecting a plurality of peripheral devices to a personal computer and now attracts much attention. Further, peripheral devices having a port for USB (hereinafter referred to as a USB port) have come to be used increasingly. 
     The employment of the USB enables commonization of interfaces of mice, keyboards, printers, modems, speakers, joy sticks, etc. that are separate from each other conventionally. Further, equipping a personal computer main body with only one USB port enables up to 127 peripheral devices of the above kinds to be connected to each other in star-like form if a USB hub apparatus is used. 
     Such an apparatus having a USB port (hereinafter abbreviated as a USB apparatus) and a hub apparatus that has a USB port and serves to connect a plurality of USB apparatuses (hereinafter abbreviated as a USB hub apparatus) are also constructed in such a manner that if they have not communicated with the host computer for a predetermined time or more, a sleep mode as mentioned above is established. 
     However, in such USB apparatuses and USB hub apparatuses, a USB control section, internal circuits, a preheating circuit, etc. are always supplied with power in case the personal computer restarts a transmission. This results in a problem that even if, for example, the power of the personal computer is off, a certain amount of power continues to be consumed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above circumstances, and an object of the invention is therefore to provide a USB apparatus and a USB hub apparatus which can reduce power that is consumed by the USB apparatus or the USB hub apparatus in a state that the power of a personal computer is off. 
     To attain the above object, the invention provides a USB apparatus which is connected to a host computer and transmits and receive information to and from it according to a protocol that complies with a USB standard, comprising power supplying means for supplying power to each section of the USB apparatus; power supply voltage detecting means for detecting presence/absence of a power supply voltage to be supplied from the host computer; and supply power control means for controlling the power that is supplied by the power supplying means in accordance with a detection result of the power supply voltage detecting means. 
     The power supplying means supplies power to each section of the USB apparatus. The power supply voltage detecting means detects presence/absence of a power supply voltage to be supplied from the host computer. The supply power control means controls the power that is supplied by the power supplying means in accordance with a detection result of the power supply voltage detecting means. 
     For example, the power supplying means supplies power to each section of the USB apparatus. The power supply voltage detecting means detects presence/absence of a power supply voltage to be supplied from the host computer via a “V bus +5 V” terminal of a USB port. Referring to a detection result of the power supply voltage detecting means, the supply power control means allows the supply of power to internal circuits if the power supply voltage is supplied to the “V bus +5 V” terminal, and stops the supply of power to the internal circuits if the power supply voltage is not supplied to the “V bus +5 V” terminal. 
     Further, to attain the above object, the invention provides a USB hub apparatus which interconnects a host computer to one or more USB apparatuses and allows transmission and reception of information to be performed between the host computer and the USB apparatuses according to a protocol that complies with a USB standard, comprising power supplying means for supplying power to each section of the USB hub apparatus; power supply voltage detecting means for detecting presence/absence of a power supply voltage to be supplied from the host computer; and supply power control means for controlling the power that is supplied by the power supplying means in accordance with a detection result of the power supply voltage detecting means. 
     The power supplying means supplies power to each section of the USB hub apparatus. The power supply voltage detecting means detects presence/absence of a power supply voltage to be supplied from the host computer. The supply power control means controls the power that is supplied by the power supplying means in accordance with a detection result of the power supply voltage detecting means. 
     For example, the power supplying means supplies power to each section of the USB hub apparatus. The power supply voltage detecting means detects presence/absence of a power supply voltage to be supplied from the host computer via a “V bus +5 V” terminal of a USB port. Referring to a detection result of the power supply voltage detecting means, the supply power control means allows the supply of power to internal circuits if the power supply voltage is supplied to the “V bus +5 V” terminal, and stops the supply of power to the internal circuits if the power supply voltage is not supplied to the “V bus +5 V” terminal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the principle of the present invention; 
     FIG. 2 is a block diagram showing an example configuration of a system according to an embodiment of the invention; 
     FIG. 3 is a block diagram showing a detailed configuration example of part of a USB hub apparatus shown in FIG. 2; 
     FIG. 4 is a block diagram showing a detailed configuration example of a series power supply shown in FIG. 3; 
     FIG. 5 is a block diagram showing a detailed configuration example of part of a USB apparatus  30  shown in FIG. 2; 
     FIG. 6 is a block diagram showing a detailed configuration example of a switching power supply shown in FIG. 5; and 
     FIG. 7 is a block diagram showing a detailed configuration example of part of a USB apparatus  31  shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be hereinafter described with reference to the accompanying drawings. 
     FIG. 1 shows the principle of the invention. As shown in FIG. 1, a USB apparatus (or a USB hub apparatus)  1  is USB-connected to a personal computer  2  serving as a host computer to enable transmission and reception of data. 
     The USB apparatus  1  is composed of a USB port  1   a , a power supply voltage detecting means  1   b , a supply power control means  1   c , and a power supplying means  1   d . The USB apparatus  1  is a printer, a modem, a scanner, or the like. 
     The USB port  1   a  is a serial interface, and transmits and receives data to and from the personal computer  2 . The power supply voltage detecting means  1   b  detects whether a power supply voltage “+5 V” is supplied from a “V bus +5 V” terminal of the USB port  1   a . The supply power control means  1   c  controls, in accordance with a detection result of the power supply voltage detecting means  1   b , the power that is supplied by the power supplying means  1   d . The power supplying means  1   d  supplies power to each section of the USB apparatus  1 . 
     Next, the operation of the system of FIG. 1 will be described. 
     Now, assume that the power switch of the USB apparatus  1  has been turned on in a state that the power switch of the personal computer  2  is off. In response, the power supplying means  1   d  tries to start supplying power to each section of the apparatus. 
     Since in this state the power of the personal computer  2  is off, no voltage is applied to the “V bus +5 V” terminal of the USB port  1   a . The power supply voltage detecting means  1   b  detects that no power supply voltage is applied to the “V bus +5 V” terminal and informs the supply power control means  1   c  of that fact. 
     The supply power control means  1   c  controls the power supplying means  1   d  to establish a state that the supply of power is stopped or low power is supplied. As a result, the USB apparatus  1  is rendered in a state that each section of the apparatus is not supplied with power though the power switch is on. 
     If the power switch of the personal computer  2  is turned on in this state, a power supply voltage “+5 V” is applied to the “V bus +5 V” terminal of the USB port  1   a.    
     As a result, the power supply voltage detecting means  1   b  detects that the power supply voltage is applied to the “V bus +5 V” terminal and informs the supply power control means  1   c  of that fact. 
     The supply power control means  1   c  controls the power supplying means  1   d  to have it start supplying power to each section of the apparatus. As a result, the USB apparatus  1  is rendered operational. 
     If the power switch of the personal computer  2  is again turned off in this state, a state is established that the power supplying means  1   d  of the USB apparatus  1  to each section of the apparatus does not supply power or supplies low power to each section, in the same manner as in the above case. 
     A USB hub apparatus has a configuration and operation similar to the above, and hence descriptions therefor are omitted. 
     As described above, according to the USB apparatus and the USB hub apparatus of the invention, the supply of power to each section of the apparatus is stopped or low power is supplied to each section in a case where the power of the personal computer  2  is off. This makes it possible to reduce the power consumption. 
     Next, an example configuration of a system according to the embodiment of the invention will be described with reference to FIG.  2 . 
     As shown in FIG. 2, a personal computer  10  is equipped with a USB port  10   a  and hence can transmit and receive data to and from a USB apparatus  30  and a USB hub apparatus  20 . 
     The USB hub apparatus  20  connects the personal computer  10  to USB apparatuses  31  and  32  via a USB port  20   a  and thereby enables data transmission and reception between them. 
     The USB apparatuses  30 - 32  are equipped with respective USB ports  30   a - 32   a , and transmit and receive data to and from the personal computer  10 . 
     Symbol “Up” in each USB port means “up stream” and indicates that a signal is input thereto. Symbol “Down” means “down stream” and indicates that a signal is output therefrom. 
     FIG. 3 shows a detailed configuration example of part of the USB hub apparatus  20  shown in FIG.  2 . 
     As shown in FIG. 3, the USB port  20   a  is composed of a “V bus +5 V” terminal at which a power supply voltage is supplied from the personal computer  10  to the USB port  20   a , “D+” and “D−” terminals for data input/output, and a “GND” terminal that is connected to the chassis. 
     An amplification circuit  20   b  amplifies a voltage that is applied to the “V bus +5 V” terminal at a predetermined gain and outputs a resulting voltage. A series power supply  20   c , which is a power supply circuit, supplies DC power to the internal circuits of the USB hub apparatus  20 . A supply power control section  20   d , which is incorporated in the series power supply  20   c , controls the power that is supplied from the series power supply  20   c  to the internal circuits. 
     Next, a detailed configuration example of the series power supply  20   c  shown in FIG. 3 will be described with reference to FIG.  4 . 
     As shown in FIG. 4, the series power supply  20   c  is composed of a control section  40 , a comparison section  41 , a reference voltage section  42 , and a control switch  43 . 
     The control section  40  converts a DC voltage that includes a variable component and is supplied from a rectification circuit (not shown; circuit for lowering and rectifying a commercial power supply voltage) to a constant DC voltage and outputs it. 
     The comparison section  41  compares a voltage Vout that is output from the control section  40  with a reference voltage Vref that is output from the reference voltage section  42 , and controls the control section  40  so that the ratio of Vout to Vref is kept constant. That is, Vout is Vref multiplied by a predetermined value. 
     The reference voltage section  42  is formed by a Zener diode, for example, and generates the reference voltage Vref. 
     The control switch  43 , which corresponds to the supply power control section  20   d  shown in FIG. 3, is connected to the output terminal of the amplifying circuit  20   b . The control switch  43  is rendered in an on-state (conductive state) when the power supply voltage is not applied to the “V bus +5 V” terminal, and is rendered in an off-state (open state) when “+5 V” is applied to the “V bus +5 V” terminal. 
     As a result, the reference voltage Vref that is the predetermined voltage is output from the reference voltage section  42  when the power supply voltage is applied to the “V bus +5 V” terminal, and the output level of the reference voltage section  42  becomes the ground level (=0 V) when the power supply voltage is not applied to the “V bus +5 V” terminal. 
     Now, a description will be made of correspondence (just an example) between the principle diagram of FIG.  1  and the embodiment of FIGS. 3 and 4. 
     The USB port  1   a  corresponds to the USB port  20   a . The power supply voltage detecting means  1   b  corresponds to the amplification circuit  20   b . The supply power control means  1   c  corresponds to the control switch  43 . The power supplying means  1   d  corresponds to the control section  40 . 
     Next, a detailed configuration example of the USB apparatus  30  shown in FIG. 2 will be described with reference to FIG.  5 . 
     As shown in FIG. 5, the USB apparatus  30  is composed of a USB port  30   a , a protective resistor  30   b , a photocoupler  30   c , and a switching power supply  30   d . The switching power supply  30   d  has a supply power control section  30   e.    
     The USB port  30   a  is composed of a “V bus +5 V” terminal at which a power supply voltage is supplied from the personal computer  10 , “D+” and “D−” terminals for data input/output, and a “GND” terminal that is connected to the chassis. 
     The protective resistor  30   b  prevents an LED (light-emitting diode) incorporated in the photocoupler  30   c  from being damaged by an excess current flowing through it. 
     The photocoupler  30   c  supplies a voltage corresponding to the voltage at the “V bus +5 V” terminal of the USB port  30   a  to the supply power control section  30   e  of the switching power supply  30   d  while isolating those from each other electrically. 
     The switching power supply  30   d  generates a predetermined voltage by lowering, through switching, a voltage of about 100 V that is supplied from a commercial power supply, and supplies the generated voltage to the internal circuits. 
     The supply power control section  30   e , which is incorporated in the switching power supply  30   d , controls the power that is supplied from the switching power supply  30   d  to the internal circuits. 
     Next, a detailed configuration example of the switching power supply  30   d  shown in FIG. 5 will be described with reference to FIG.  6 . 
     As shown in FIG. 6, the switching power supply  30   d  is composed of a switching section  50 , a smoothing coil  51 , a comparison section  52 , a reference voltage section  53 , a PWM control section  54 , and a control switch  55 . 
     The switching section  50  lowers a DC voltage of about 100 V that is supplied from a rectification circuit (not shown; circuit for lowering and rectifying a commercial power supply voltage) to a predetermined voltage through switching and outputs it. 
     The smoothing coil  51  generates a DC voltage by smoothing a rectangular wave that is output from the switching section  50 , and outputs it. 
     The comparison section  52  compares an output voltage Vout of the smoothing coil  51  with a reference voltage Vref that is supplied from the reference voltage section  53 , and outputs a comparison result to the PWM control section  54 . 
     The PWM (pulse width modulation) control section  54  controls the switching section  50  in accordance with the comparison result of the comparison section  52 . 
     The control switch  55  is connected to the output terminal of the photocoupler  30   c . The control switch  55  is rendered in an on-state (conductive state) when the power supply voltage is not applied to the “V bus +5 V” terminal, and is rendered in an off-state (open state) when “+5 V” is applied to the “V bus +5 V” terminal. 
     As a result, the reference voltage Vref that is the predetermined voltage is output from the reference voltage section  53  when the power supply voltage is applied to the “V bus +5 V” terminal, and the output level of the reference voltage section  53  becomes the ground level (=0 V) when the power supply voltage is not applied to the “V bus +5 V” terminal. 
     Next, a detailed configuration example of the USB apparatus  31  shown in FIG. 2 will be described with reference to FIG.  7 . The USB apparatus  31  is one having a preheating circuit as in the case of a printer, for example. 
     As shown in FIG. 7, the USB apparatus  31  is composed of a USB port  31   a , a protective resistor  31   b , and a series power supply  31   c . The series power supply  31   c  has a supply power control section  31   d.    
     The USB port  31   a  is composed of a “V bus +5 V” terminal at which a power supply voltage is supplied from the personal computer  10  via the USB hub apparatus  20 , “D+” and “D−” terminals for data input/output, and a “GND” terminal that is connected to the chassis. 
     The protective resistor  31   b  prevents the supply power control section  31   d  from being damaged by an excess current flowing through it. 
     The series power supply  31   c  is a power supply circuit and supplies DC power to the internal circuits of the USB apparatus  31 . 
     The supply power control section  31   d , which is incorporated in the series power supply  31   c , controls the power that is supplied from the series power supply  31   c  to the internal circuits. 
     Since the series power supply  31   c  has the same configuration as shown in FIG. 4, it is not described any further. 
     Next, the operation of the above-configured system according to embodiment will be described. 
     Now, it is assumed that the power switches of all of the apparatuses are off in the system shown in FIG.  2 . If the power switch of the USB hub apparatus  20 , for example, is turned on in this state, a voltage is applied to the control section  40  shown in FIG. 4 from the rectification circuit (not shown). 
     Since the personal computer  10  is not powered in this state, the voltage at the “V bus +5 V” terminal is 0 V. Therefore, the control switch  43  is on and hence the output of the reference voltage section  42  is 0 V. 
     The comparison section  41  and the control section  40  perform a control so that the output voltage Vout has a value that is the reference voltage Vref multiplied by a predetermined value. Since Vref is 0 V, Vout becomes 0 V. 
     As a result, the internal circuits of the USB hub apparatus  20  are not supplied with power even though the power switch is turned on. 
     Since the power supply voltage is not supplied to the “V bus +5 V” terminal of the USB  30   a  of the USB apparatus  30  either, the output voltage of the photocoupler  30   c  becomes 0 V. 
     As a result, the control switch  55  of the switching power supply  30   d  is on as in the case of the control switch  43  and hence the reference voltage Vref of 0 V is supplied from the reference voltage section  53 . 
     For example, the comparison section  52  controls the PWM control section  54  so that the output voltage Vout of the smoothing coil  51  is kept equal to the reference voltage Vref. Therefore, the output voltage Vout becomes 0 V when the reference voltage Vref is 0 V. 
     As a result, even if the power switch is turned on, no power is supplied to the internal circuits of the USB apparatus  30 . 
     Further, the series power supply  31   c  of the USB apparatus  31  performs the same operation as the above-described operation in the USB hub apparatus  20 , to establish a state that no power is supplied to the preheating circuit. 
     Next, if the power switch of the personal computer  10  is turned on in a state that the power switches of all the apparatuses other than the personal computer  10  are on, the voltage at the “V bus +5 V” terminal of the personal computer becomes +5 V. 
     As a result, the power supply voltage +5 V is also applied to the “V bus +5 V” terminal of the USB hub apparatus  20 , whereby the amplification circuit  20   b  outputs the predetermined voltage. 
     Receiving the voltage from the amplification circuit  20   b , the control switch  43  is turned off, whereupon the reference voltage section  42  outputs the reference voltage Vref that is the predetermined voltage. As a result, the control section  40  outputs the predetermined DC voltage, which is supplied to the internal circuits. The USB hub apparatus  20  is thus rendered operational. 
     Since the power supply voltage +5 V is applied from the personal computer  10  to the “V bus +5 V” terminal of the USB apparatus  30 , the predetermined voltage is output from the photocoupler  30   c.    
     Receiving the output voltage of the photocoupler  30   c , the control switch  55  of the switching power supply  30   d  is turned off, whereupon the reference voltage section  53  outputs the reference voltage Vref that is the predetermined voltage (≠0 V). Since the comparison section  52  controls the PWM control section  54  so that the output voltage Vout is kept equal to the reference voltage Vref, the output voltage Vout becomes the predetermined voltage. 
     As a result, the predetermined DC voltage is supplied to the internal circuits of the USB apparatus  30 . 
     Further, the power supply voltage +5 V is also supplied from the personal computer  10  to the “V bus +5 V” terminal of the USB apparatus  31  via the USB hub apparatus  20 . As a result, the same operation in the USB hub apparatus  20  shown in FIG. 4 is performed, whereby the DC voltage is supplied to the preheating circuit. The USB apparatus  31  is thus rendered operational. 
     Next, assume that the power switch of the USB hub apparatus  20 , for example, has been turned off in the above state (the power switches of all of the apparatuses are on). In this case, the supply of the voltage from the rectification circuit (not shown) to the control section  40  is stopped, and hence the supply of the voltage to the internal circuits is stopped irrespective of the state of the “V bus +5 V” terminal. The voltages of the “V bus +5 V” terminals of the USB apparatuses  31  and  32  become 0 V. 
     If the power switch of the personal computer  10  is turned off subsequently, the voltages of the “V bus +5 V” terminals of the USB ports of all the apparatuses become 0 V. 
     Therefore, for example, the control switch  55  of the switching power supply  30   d  of the USB apparatus  30  is turned on, and hence the reference voltage Vref that is output from the reference voltage section  53  becomes 0 V. As a result, the output voltage Vout also becomes 0 V. That is, a state is established that no power is supplied to the internal circuits of the USB apparatus  30 . 
     Similarly, in the series power supply  31   c  of the USB apparatus  31 , the reference voltage Vref becomes 0 V and hence the output voltage Vout becomes 0 V. As a result, a state is established that no power is supplied to the preheating circuit of the USB apparatus  31 . 
     As described above, according to the embodiment, the supply of power to the internal circuits or the preheating circuit is stopped when one of the power switch of the USB hub apparatus  20  and the USB apparatuses  30 - 32  is turned on in a state that the power switch of the personal computer  10  is off, whereby useless power consumption can be prevented. 
     In the above embodiment, the supply of power from the series power supply  20   c , the switching power supply  30   d , and the series power supply  31   c  is stopped (i.e., their output voltages are made 0 V) in a state that the power switch of the personal computer  10  is off. Alternatively, for example, the output voltages may be set at a voltage (e.g., 1 V) that is lower than in ordinary operation. 
     As described above, according to the invention, the supply of a power supply voltage to the internal circuits of a USB apparatus is stopped in a state that the USB apparatus is not supplied with a power supply voltage from the host side. Therefore, useless power consumption can be prevented with a simple circuit configuration.