Abstract:
A charging circuit and method for charging a power storage device in a power over Ethernet environment are necessary to prevent unnecessary power consumption. Power sourcing equipment continuously supplies power to a connected device after determining that the device is compatible. In order to prevent supply of power after a power storage device attains full charge, a charging circuit may include an interface for supplying electric power; a sensing circuit including a switch in series with a resistor; and a voltage detection circuit. The voltage detection circuit may communicate with the sensing circuit and may output a first signal that turns the switch OFF when the voltage of the power storage device is greater than or equal to a first voltage and may output a second signal that turns the switch ON when the voltage of the power storage device is less than or equal to a second voltage.

Description:
BACKGROUND 
     Many modern network-connectable, electronic devices require data connectivity as well as connection to power supplies. IP telephones, wireless LAN access points, Bluetooth access points, web cameras, digital still and video cameras, computers, tablets, liquid crystal displays, point-of-sale kiosks, network intercom systems, cellular telephones, security systems, gaming systems, etc. are examples of devices that require both data connectivity as well as connection to power supplies. Traditionally, each of these electronic devices had separate cables for data connectivity and power supply. With the advent of implementation of IEEE 802.3.af and IEEE 802.3.at standards, which are extensions of the existing Ethernet standard, power over Ethernet capability (i.e., supplying power over Ethernet cables) has become more common. 
     There are many advantages to supplying power over Ethernet. For example, power over Ethernet may result in more flexible network design because the powered devices can be situated in areas without access to power outlets. This may also result in cost savings because it removes the need to install additional power outlets. In addition, power over Ethernet may be safer because there is no need to deploy AC main power throughout the network. Thus, additional electronic devices will be designed to receive power over Ethernet for the reasons above, as well as because of higher power supply capabilities permitted under the standards. This is especially the case because the cost of adding power supplies to Ethernet switches is relatively low. 
     According to the existing standards, power sourcing equipment (PSE) executes a discovery process to determine whether a compatible device is connected to it before supplying power in order to prevent damage to the connected device. The PSE makes this determination by applying a relatively low voltage to the network cable and checking for the presence of a sensing resistor in the connected device. The PSE only supplies the full voltage after detecting the sensing resistor in the connected device. However, if the connected device includes a chargeable power storage device, the PSE continues to supply the full voltage so long as the PSE senses the sensing resistor, even after the power storage device attains full charge. This results in unnecessary power consumption. 
     SUMMARY 
     Disclosed herein are apparatuses and methods for charging a power storage device. A charging circuit for charging a power storage device in a power over Ethernet environment according to one implementation may include an interface for supplying electric power to the power storage device; a sensing circuit including a resistor and a switch that is disposed in series with the resistor; and a voltage detection circuit that detects a voltage of the power storage device. The voltage detection circuit may communicate with the sensing circuit and may output a first signal that turns the switch OFF when the voltage of the power storage device is greater than or equal to a first voltage and may output a second signal that turns the switch ON when the voltage of the power storage device is less than or equal to a second voltage. 
     In one example implementation, the supply of the electric power to the power storage device may be interrupted when the switch is OFF and uninterrupted when the switch is ON. 
     In another example implementation, the supply of the electric power to the power storage device may be interrupted by preventing current from flowing through the resistor. 
     Optionally, the first voltage may be approximately equal to the voltage of the power storage device when fully charged and the second voltage may be approximately equal to the voltage of the power storage device when drained. Alternatively or additionally, the first voltage and the second voltage may be variable. 
     The charging circuit may optionally include a resistor having a value between 19 and 26.5 kΩ. Further, the switch may optionally be a MOSFET. 
     In another example implementation, an electronic device may include the charging circuit discussed above. For example, the electronic device may be an IP telephone, a wireless LAN access point, a Bluetooth access point, a web camera, a digital camera, a cellular telephone, a computer, a tablet, a PDA, etc., or any other portable electronic device. 
     A charging circuit according to another example implementation may include an interface for supplying electric power to the power storage device; a sensing circuit including a resistor with a value between 19 and 26.5 kΩ and a switch that is disposed in series with the resistor; and a voltage detection circuit that detects a voltage of the power storage device. The voltage detection circuit may communicate with the sensing circuit and may output a first signal that turns the switch OFF when the voltage of the power storage device is greater than or equal to a first voltage and may output a second signal that turns the switch ON when the voltage of the power storage device is less than or equal to a second voltage. 
     In one example implementation, the supply of the electric power to the power storage device may be interrupted when the switch is OFF and uninterrupted when the switch is ON. 
     In another example implementation, the supply of the electric power to the power storage device may be interrupted by preventing current from flowing through the resistor. 
     Optionally, the first voltage may be approximately equal to the voltage of the power storage device when fully charged and the second voltage may be approximately equal to the voltage of the power storage device when drained. Alternatively or additionally, the first voltage and the second voltage may be variable. 
     The charging circuit may optionally include a MOSFET as the switch. 
     In another example implementation, an electronic device may include the charging circuit discussed above. For example, the electronic device may be an IP telephone, a wireless LAN access point, a Bluetooth access point, a web camera, a digital camera, a cellular telephone, a computer, a tablet, a PDA, etc., or any other portable electronic device. 
     A method for charging a power storage device in a power over Ethernet environment including a power source device and a powered device having a sensing resistor and a switch in series with the sensing resistor according to another example implementation may include monitoring voltage of the power storage device; preventing power from being supplied to the power storage device when the monitored voltage is greater than or equal to a first voltage by turning the switch OFF; and receiving power at the power storage device when the monitored voltage is less than or equal to a second voltage by turning the switch ON. 
     The method may optionally include outputting a first signal when the monitored voltage is greater than or equal to the first voltage, the first signal turning the switch OFF; and outputting a second signal when the monitored voltage is less than or equal to the second voltage, the second signal turning the switch ON. Alternatively or additionally, preventing power from being supplied to the power storage device may include preventing current from flowing through the sensing resistor. 
     Other apparatuses, methods, features and/or advantages will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional apparatuses, methods, features and/or advantages be included within this description and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views. 
         FIGS. 1A and 1B  illustrates example block diagrams of systems for supplying power in a power over Ethernet environment; 
         FIGS. 2A and 2B  illustrates example circuit diagrams of power transmission in a power over Ethernet environment; 
         FIG. 3  illustrates an example circuit diagram of a charging circuit according to one example implementation of the invention; and 
         FIG. 4  illustrates an example flow diagram of a method for charging a power storage device in a power over Ethernet environment according to one example implementation of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. While implementations will be described for a charging power storage device in a power over Ethernet environment, it will become evident to those skilled in the art that the implementations are not limited thereto. 
     Referring to  FIGS. 1A and 1B , simplified block diagrams of systems for supplying power in a power over Ethernet environment are illustrated. The systems comprise a data transmission/reception device  102 , a PSE  104  and a powered device  106 . The data transmission/reception device  102  may be an Ethernet switch, for example. In addition, the powered device  106  may be connected to the data transmission/reception device  102  and/or the PSE  104  using a network cable, such as CAT 3, CAT 5 or CAT 5e cable, for example. In a power over Ethernet environment, both data and power may be supplied over the same network cable. 
       FIG. 1A  illustrates a system including a midspan power source. In this implementation, the PSE  104  injects power between the data transmission/reception device  102  and the powered device  106 . In other words, the PSE  104  is separate and distinct from the data transmission/reception device  102 . Typically, a midspan power source is utilized when the data transmission/reception device  102  does not include a power source. On the other hand,  FIG. 1B  illustrates a system including an endspan power source. In this implementation, the PSE  104  is included within the data transmission/reception device  102 . As discussed above, the cost of adding the PSE  104  to the data transmission/reception device  102  is relatively low. 
     The powered device  106  may include a charging circuit  107  having a sensing circuit  108 , a voltage detection circuit  110 , an interface circuit  112 , a DC/DC converter  113  and a power storage device  114 , for example. The charging circuit may also include a rectifier circuit such as a bridge rectifier, for example, for converting AC current into DC current. The sensing circuit  108 , the voltage detection circuit  110  and the interface circuit  112  are discussed in detail with regard to  FIG. 3 . The DC/DC converter  113  may be utilized to convert the voltage output by the PSE  102  to a lower voltage required by the powered device  106 . For example, if the PSE  104  outputs a voltage in a range between 44 and 57 V, the DC/DC converter  113  may convert this voltage to a lower voltage such as 3, 5 or 12 V, as required by the powered device  106 . 
     The powered device  106  may be any electronic device that requires electrical power during operation. Additionally, the powered device  106  may also require data connectivity during operation. IP telephones, wireless LAN access points, Bluetooth access points, web cameras, digital still and video cameras, computers, tablets, liquid crystal displays, point-of-sale kiosks, network intercom systems, cellular telephones, security systems, gaming systems, etc. are examples of a powered device  106 . One skilled in the art, however, would understand that the powered device  106  is not limited to these devices, and may also include any portable electronic device that requires electrical power and/or data connectivity during operation. 
       FIGS. 2A and 2B  illustrate example circuit diagrams of power transmission in a power over Ethernet environment. These circuits may include a data transmission/reception circuit  202  having a PSE  204  and a powered device  206 . As discussed above, in some implementations, the PSE  204  may not be included in the data transmission/reception circuit  202 , and instead may be disposed in between the data transmission/reception circuit  202  and the powered device  206 . In addition, the powered device  206  may include a charging circuit  207  and a power storage device  214  as well as the additional circuits discussed with regard to  FIGS. 1A ,  1 B and  3 . The data transmission/reception circuit  202  may be connected to the powered device  206  with a network cable  220 . The network cable  220  may be an Ethernet cable such as CAT3, CAT5 or CAT5e cable, for example. 
     The network cable  220  may be implemented using Ethernet over twisted pair technology. For example, the network cable  220  may include four pairs of twisted wires. In systems complying with the 10BASE-T and 100BASE-TX Ethernet standards, only two of the four pairs of twisted wires are utilized for data transmission. Thus, power may be transmitted over the data transmission/reception twisted pairs  222  or the spare twisted pairs  224 . On the other hand, although not illustrated, in systems complying with the 1000BASE-T Ethernet standard, all four pairs of twisted wires are utilized for data transmission. Thus, power must be transmitted over the data transmission/reception twisted pairs. 
       FIG. 2A  illustrates one example circuit diagram of power transmission in a power over Ethernet environment. As discussed above, the data transmission/reception circuit  202  may be connected to the powered device  206  using the network cable  220 . In  FIG. 2A , the data may be transmitted over the data transmission/reception twisted pairs  222 . For example, the data may be transferred/received over the pair on pins  1  and  2  and the pair on pins  3  and  6  of a CAT 5 or CAT 5e cable, respectively. Alternatively or additionally, power may be supplied over the data transmission/reception twisted pairs  222 . It is possible to transfer power over the data transmission/reception twisted pairs  222  by using the center taps of the data transmission transformer  226  and the data reception transformer  228  because the pairs are transformer coupled at each end, i.e., it is possible to apply DC power to the center tap of the isolation transformer without interfering with the data transfer. Optionally, a voltage of either positive or negative polarity may be applied to the center tap of either the data transmission transformer  226  or the data reception transformer  228 . 
       FIG. 2B  illustrates another example circuit diagram of power transmission and a power over Ethernet environment. Similarly to  FIG. 2A , the data transmission/reception circuit  202  may be connected to the powered device  206  using the network cable  220 . However, in  FIG. 2B , power is transferred over the spare twisted pairs  224 . For example, power may be transferred over the pair on pins  4  and  5  and the pair on pins  7  and  8  of a CAT 5 or CAT 5e cable. Optionally, a voltage of either positive or negative polarity may be applied to either of the spare twisted pairs  224 . 
     Referring to  FIG. 3 , an example circuit diagram of a charging circuit according to an example implementation is illustrated. The charging circuit  307  may include a rectifier circuit  301 , a sensing circuit  308 , an interface circuit  312 , a voltage detection circuit  310  and a power storage device  314 . Power is received from the PSE through the twisted pairs  330 . 
     According to existing Ethernet standards, in order to prevent damage to the powered devices connected to the PSE, the PSE executes a sensing process. Particularly, the PSE searches for powered devices that comply with the existing standards. For example, the PSE applies a relatively low voltage to the network cable and checks for the presence of a sensing resistor in the connected device. In preferred implementations, the sensing resistor may have a value in a range between 19 and 26.5 kΩ. For example, in some implementations, the sensing resistor may be 25 kΩ. Optionally, the value of the resistor may vary from the above range by 10%. In addition, the relatively small voltage may be approximately 2.7 to 10.1 V, for example. The PSE applies the full voltage (i.e., supplies power to the connected device) only after detecting the sensing resistor. The full voltage may be in a range between 44 and 57 V, for example. In other words, if the PSE does not detect the sensing resistor, the PSE does not supply power to the powered device. As discussed above, the PSE will continue to supply power to the powered device so long as it detects the sensing resistor, even after the power storage device attains full charge. This may result in unnecessary power consumption. 
     As shown in  FIG. 3 , a charging circuit  307  includes a sensing circuit  308  having a sensing resistor  309  in series with a switch  311 . In some implementations, the value of the sensing resistor may preferably have a value between 19 and 26.5 kΩ for example, 25 kΩ. In addition, the switch  311  may be a MOSFET. Alternatively, the switch may be another semiconductor device, transistor, logic gate, etc., or combination thereof. 
     In order to prevent unnecessary power consumption, the sensing resistor  309  is “removed” from the charging circuit  307 , which causes the PSE to cease supplying power to the powered device because it no longer detects the sensing resistor. Accordingly, the PSE believes that the powered device has been removed from the port when it does not detect the sensing resistor. However, in actuality, the powered device remains connected to the port, and the powered device may continue to transmit/receive data, but the powered device will no longer receive power from the PSE. Thus, the charging circuit  307  is controlled such that the PSE stops supplying power to the powered device when the power storage device attains full charge. 
     Referring to  FIG. 3 , a voltage detection circuit  310  detects the voltage of the power storage device  314 . When the voltage of the power storage device  314  is greater than or equal to a predetermined voltage, the voltage detection circuit  310  outputs a signal that causes the switch  311  to turn off (i.e., to open). This prevents current from flowing through the sensing resistor  309 , which prevents the PSE from detecting the sensing resistor  309  and causes the PSE to interrupt the supply of power to the powered device. The predetermined voltage may be approximately equal to the voltage of the power storage device  314  when fully charged. Optionally, the predetermined voltage may be variable because it depends on the specific operating characteristics of the power storage device. 
     In addition, when the voltage of the power storage device  314  is less than or equal to a predetermined voltage, the voltage detection circuit  310  outputs a signal that causes the switch  311  to turn on (i.e., to close). This allows current to flow through the sensing resistor  309 , which allows the PSE to detect the sensing resistor  309  and causes the PSE to supply power to the powered device. The predetermined voltage may be approximately equal to the voltage of the power storage device  314  when drained. Optionally, the predetermined voltage may be variable because it depends on the specific operating characteristics of the power storage device. 
     Referring to  FIG. 4 , an example flow diagram of a method for charging a power storage device in a power over Ethernet environment according to one example implementation is illustrated. At  402 , the sensing resistor is detected. For example, the PSE may execute a process to detect the sensing resistor. As discussed above, the PSE may apply a relatively small voltage to the network cable and check for the sensing resistor. The PSE will only supply power to the powered device after detecting the sensing resistor. 
     At  404 , the voltage of the power storage device is monitored. When the voltage of the power storage device is greater than or equal to a predetermined voltage, a control signal is output at  406  in order to open the sensing circuit and prevent the PSE from detecting the sensing resistor, which causes the PSE to cease supplying power to the powered device. When the voltage of the power storage device is less than or equal to a predetermined voltage, a control signal is output at  406  in order to close the sensing circuit and allow the PSE to detect the sensing resistor, which causes the PSE to supply power to the powered device. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.