Abstract:
A peripheral device has a bus-controlled switching arrangement for operating a power supply. A device comprises a bus interface adapted for communicating with a remote device via a bus. A switch circuit is connected between the bus interface and a power supply. The switch circuit is operative, when the power supply is in an inactive state, for sensing bus activity and for generating a signal for activating the power supply in response to the sensed bus activity, wherein the switch circuit has no power dissipation when no activity is sensed on the bus.

Description:
RELATED APPLICATIONS 
   This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/IB03/05478, filed Oct. 16, 2003, which was published in accordance with PCT Article 21(2) on Apr. 29, 2004 in English and which claims the benefit of U.S. provisional patent application No. 60/419,632, filed Oct. 18, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates generally to power supplies, and more particularly, to techniques for turning on and off power supplies. 
   BACKGROUND OF THE INVENTION 
   Peripheral devices such as routers, hubs, printers, scanners and the like, are often connected to a computer and/or to one another via one or more bus systems. In relatively small networks like SOHO (Small Office and Home Office) and DHT (Digital Home networks), most of the peripheral devices are turned on via a central power switch, or by turning on each of the devices individually. However, this activation operation becomes more inconvenient when the peripheral device is not in the same room as the computer. The power control problem is exacerbated when multiple peripheral devices are located remote from one another and/or from the computer(s) in the network. Consequently, such devices are often not turned off, but rather left in standby mode, thereby constantly consuming power. A peripheral device that senses bus inactivity, while maintaining the device without dissipating power in the sensing circuitry when there is no activity on the bus, is highly desired. 
   SUMMARY 
   A peripheral device has a bus-controlled switching arrangement for operating a power supply. The device comprises a bus interface adapted for communicating with a remote device via a bus. A switch circuit is connected between the bus interface and a power supply. The switch circuit is operative, when the power supply is in an inactive state, for sensing bus activity and for generating a signal for activating the power supply in response to the sensed bus activity, wherein the switch circuit has no power dissipation when no activity is sensed on the bus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exemplary illustration of a peripheral device having a bus-controlled switching arrangement useful for understanding the principles of the present invention. 
       FIG. 2  is another exemplary illustration of a peripheral device having a bus-controlled switching arrangement useful for embodying the principles of the present invention. 
       FIG. 3  is another exemplary illustration of a peripheral device having a bus-controlled switching arrangement useful for embodying the principles of the present invention. 
       FIG. 4  is another exemplary illustration of a peripheral device having a bus-controlled switching arrangement useful for embodying the principles of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a peripheral device  10 , such as a printer, connected to another electronic device  20  such as a computer, via bus  25  connected to bus interface  30 . Note that device  10  may be connected directly to external device  20  via bus  25  and bus interface  30 , or may be coupled through a computer network, such as an Ethernet network. As shown in  FIG. 1 , bus interface  30  comprises a universal synchronous bus (USB) connector for communicating power and/or data signals to and/or from printer  10 . In the embodiment shown in  FIG. 1 , a pair of input lines  34  convey data signals to USB controller  12  from computer  20 . Power lines  32  convey power signals from the computer  20  via connector  30  to a power switch  40 . Power switch  40  may comprise a simple relay, a solid state switch, or any other switching device capable of switchably connecting the mains power connection  50  with power supply  60 . In operation, when computer  20  is powered on, the USB power line  32  becomes active, causing switch  40  to close, thereby activating power supply  60  and enabling power to be provided to controller  12  for processing the data received from the external device. It is understood that, upon activation, the device may enter either a standby mode or a run mode of operation. When computer  20  is turned off or the USB connection is removed, the signal on power lines  32  causes switch  40  to change state or “open”, thereby disabling connection of power supply  60  from mains connection  50 , and hence automatically turning printer  10  “off”. 
     FIG. 2  illustrates an exemplary system useful for embodying an aspect of the present invention. As shown in  FIG. 2 , bus interface  30 ′ comprises an Ethernet connector for connecting peripheral device  10 ′ to an external device (not shown) via bus  25 ′. In this embodiment, a bus system is implemented without a power distribution from an external device. A pair of input lines  34 ′ from connector  30 ′ convey data signals to ethernet controller  12 ′. A pair of output lines  36  carry output signals from controller  12 ′ to ethernet connector  30 ′ for transfer onto bus  25  for routing to an external device on the network. In networks such as Ethernet networks (e.g. Ethernet 10/100base-T networks), a master device (such as a PC) periodically scans bus  25  by providing periodic scanning pulses on input lines  34 ′. These scanning pulses are detected by passive signal detector  38 . The small amount of scanning energy in the scanning pulses detected by detector  38  causes the detector to generate a signal  39  to activate or turn “on” power supply  60  to provide power to controller  12 ′. 
   When the power supply  60  is activated, the controller or microcomputer  12 ′ is operable to detect at its input terminals RX+, RX−, whether or not bus  25  is used or disconnected from the system. In the event that controller  12 ′ senses the absence of bus activity over a predetermined time interval, or a disconnection of the bus interface from the system, the controller generates a command signal  62  to turn “off” the power supply  60 . 
   It is understood that a network such as an Ethernet network does not carry power. However, as previously mentioned, bus activity is characterized by pulse packages traveling on the network. These pulse packages can be detected and used for turning on the peripheral.  FIG. 3  illustrates an exemplary detailed circuit operable for sensing bus inactivity without consuming power when the peripheral device is in the inactive state. As shown in  FIG. 3 , the peripheral device includes a circuit  300  for providing this functionality. Pulse packages  23  carried on bus  25 ′ are received at ethernet bus connector  30 ′ and input to circuit  300  over signal lines  34 ′ from ports RD+, RD−. The signal lines carry the data signals indicative of bus activity to the input ports of ethernet controller/receiver  12 ′. Signal lines  34  are also connected to transformer T 1 , which isolates the bus from the power supply. The output V 1   a  of transformer T 1  is connected to the base b 1  of pnp transistor Q 1  by resistor R 3 , which provides an input impedance for the network  25 . The output V 1   b  of transformer T 1  is connected to emitter e 1  of Q 1  at node  300   b . The collector c 1  of transistor Q 1  is connected at node  300   a  to capacitor C 3 . Zener diode D 5  and resistor R 4  are connected in parallel with one another and with capacitor C 3 . Metal Oxide Semiconductor Field Effect Transistor (MOSFET) Q 2  has a gate terminal g 2  connected at node  300   a . Drain Terminal d 2  of Q 2  is connected via resistor R 2  to node  300   b  while source terminal s 2  is connected to charge capacitor C 2  at node  300   c . The value of resistor R 2  is chosen to have a relatively large value so as not to dissipate a significant amount of power during the active mode of the power supply, while still providing for sufficient current to capacitor C 2  for providing power for the switched mode power supply control circuit  74 . Switched mode power supply (SMPS)  70  is connected to node  300   c  at a first input  72  for receiving in control circuit  74  a supply voltage Vcc. SMPS  70  further includes a switch  76  responsive to the output of the control circuit  74  for periodically energizing the primary winding w 1  of transformer T 2 . 
   According to an inventive aspect, the peripheral device is arranged such that its sensing circuitry for sensing bus inactivity does not dissipate any power when in the inactive state. More particularly, when the device is inactive and there is an absence of bus activity on lines  34 ′, transistor Q 1  is off and no power is dissipated by the sensing circuitry. Because Q 1  is off, capacitor C 3  is not charged. Hence, Q 2  is also off, so that no power is dissipated in Q 2 . When no pulses are present on input lines  34 ′ transistors Q 1  and Q 2  do not dissipate energy. 
   However, as shown in  FIG. 3 , transistor Q 1  is responsive to bus activity on input lines  34 ′ for charging capacitor C 3  to cause Q 2  to be biased on. This in turn causes C 2  to charge to supply a voltage Vcc to activate the control circuit  74  of SMPS  70  to provide an output power supply voltage Vs. In particular, as shown in  FIG. 3 , pulse signals  23  indicative of bus activity are received over lines  34 ′ and isolated by step down transformer T 1 . The pulse signals input at base terminal b 1  serve to bias transistor Q 1  on so that Q 1  rectifies the isolated pulse signals and charges capacitor C 3 . The voltage across C 3  controls the operation of MOSFET Q 2 , which charges C 2 . More particularly, when the voltage across C 3  reaches a predetermined threshold level of transistor Q 2 , MOSFET transistor Q 2  is biased on to provide a current to charge capacitor C 2 . When the voltage V on C 2  reaches the threshold startup voltage Vcc, the power supply control circuit  74  is activated to generate a periodic switching signal  39  to activate switch  76  to periodically connect transformer T 2  with GND to generate a switched mode output supply voltage Vs for the peripheral device. The power supply remains active or “on” until the absence of bus activity is detected by circuit  300 , and the additional delay caused by the time constants of the R 4 , C 3 , and R 2 , C 2  circuit components. Note that the time constants provide additional noise immunity for the circuit  300 . When no pulses are present on the bus interface, C 2  eventually discharges to below a minimum operating value (Vop), causing the control circuit to be inactivated and turning off the power supply. It is understood that the minimum operating voltage value for inactivating the supply may be the same as, or, more preferably, less than, the threshold startup voltage Vcc. This is because the startup voltage is typically greater than the normal or average voltage level for operating the power supply. In any event, it is understood that a minimum operating voltage level at C 2  exists such that, when C 2  is discharged below that level, the control circuit becomes inactivated and the power supply is turned off. 
   It is understood that bypass switch S 1  provides a bypass for the above described bus-controlled mode of operation. More particularly, bypass switch S 1  enables the user to bypass Q 1 , Q 2  and associated circuitry for sensing input pulses from bus  25 ′ and activating the power supply, and instead provides current through R 2  to and S 1  to directly charge capacitor C 2 . In this configuration, when S 1  is closed, the power supply is activated upon connection with the mains voltage V mains, independent of the activity on the bus. When switch S 1  is open, the peripheral device is in remote start-up mode, wherein data signals from the bus are used to activate the power supply. Of course, as discussed above, when switch S 1  is open and no input pulse signals  23  are present on the bus, the circuitry for sensing bus inactivity does not consume any power when in the inactive state, including transistors Q 1  and Q 2 . 
   As discussed herein, the circuit of  FIG. 3  is operable such that when pulses  23  are no longer present on the input lines, the power supply is turned off after bus inactivity results in shutoff of Q 1  and Q 2 , and subsequent discharge of C 2  according to the time delays of the circuit. However, the above described shutdown method may be undesirable in certain applications, such as when a printer receives instructions from a computer to perform certain print operations, and initiates processing to execute its tasks. In this case, the peripheral device should remain active to complete print operations even when there is no bus activity on the network.  FIG. 4  illustrates an exemplary embodiment for maintaining the power supply in an active state despite an absence of bus activity. 
   As shown in  FIG. 4 , power supply  70 ′ includes additional winding w 3  connected to diode D 2 , which is coupled to capacitor C 2  through (normally closed) switch  78 . When Q 2  is on, current passes through R 2  and Q 2  to charge capacitor C 2 . When the threshold startup voltage level Vcc is reached, the control circuit  74  is activated to cause periodic switching of switch  76  to GND. This causes transformer T 2  to be periodically energized so as to transfer power to the secondary side through w 2 . In this case, the winding w 3  coupled to the primary side of T 2  and connected by diode D 2  to capacitor C 2  through switch  78  provides an additional source of power to capacitor C 2  to the control circuit  74  to effectively latch the voltage at the input of the power supply  70 ′. This ensures that C 2  is charged to the appropriate level to maintain activation of the power supply, independent of any subsequent cessation of pulse signals  23  on the bus. Therefore, the power supply of  FIG. 4  is operable such that after the power supply is initially activated (e.g. by sensing of bus activity), the device can continue operating despite a later absence of bus activity. 
   The power supply may be turned off via a control signal CI at control input  75  of power supply  70 ′. The control signal CI may be input from a microprocessor in controller/receiver  12 ′ which, after detecting the absence of signal activity on the bus over a predetermined time interval, and upon completion of its tasks (e.g. completion of printing operations), generates a control signal CI to open switch  78 . This causes C 2  to be discharged, inactivating the control circuit  74  and turning off power supply  70 ′. It is understood that the control input and shutoff functionality associated with the microprocessor receiver, as well as the latching and shutdown processes associated with the power supply, may be implemented as executable instructions in software, as circuit elements and/or components in hardware, as programmable memory in firmware, and combinations thereof. 
   Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. The appended claims should be construed broadly to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.