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  • POE power supply principle and procedure details

        POE (Power Over Ethernet) refers to the existing Ethernet cabling infrastructure Cat.5 do not make any changes to the case for a number of IP-based terminal ( such as IP telephones, wireless LAN access point AP, POE IP camera , etc. ) transmit data signals at the same time , but also for providing DC power supply such equipment technology. POE technology to ensure the safety of the existing structured cabling while ensuring the normal operation of the existing network , minimizing costs.
        I. Introduction
        PoE is also known as the power supply system based on LAN (PoL, Power over LAN) or Active Ethernet (Active Ethernet), sometimes referred to as Power over Ethernet , which is the use of existing transmission standard Ethernet cable to transmit both data and electric power of the latest standards, and maintained with existing ethernet system and user compatibility. IEEE 802.3af Power over Ethernet standard is based on the new standard POE system , it is based on the IEEE 802.3 an increase of power through the network cable directly to the relevant standards, the expansion of the existing Ethernet standard , is the first international on power distribution standards. [ 1 ]
        IEEE in 1999 began to develop the standards , the earliest participating manufacturers have 3Com, Intel, PowerDsine, Nortel, Mitel , and National Semiconductor. However, the shortcomings of the standard has been restricting the expansion of the market . Until June 2003 , IEEE approved the 802. 3af standard, which clearly defines the remote system power detection and control issues , and the routers, switches and hubs via Ethernet cable to IP phones, security systems and wireless LAN access point -powered devices such as a prescribed manner . IEEE 802.3af contains many development efforts of the company experts , which also makes this standard can be tested in all respects .
        A typical Ethernet power supply system. Retained in the wiring closet Ethernet switch equipment, with a hub with a power supply (Midspan HUB) to provide power to the LAN UTP . In the twisted end of the power used to drive phones, wireless access points, cameras and other devices. To avoid power outages , you can use a UPS.
        Second, the principle
        Standard UTP cable has four twisted pairs , but l0M BASE-T and 100M BASE-T uses only one of the two pair. IEEE80 2.3af allows two kinds of usage, the application is idle foot powered, 4,5 pin connector is positive , 7,8 pin connection is the negative. When application data pin power supply , the DC power applied to the transmit transformer the midpoint does not affect the data transmission. In this way downline pair of 1,2 and 3,6 can be any polarity.
        Standard does not allow application of the above two cases simultaneously . PSE power supply devices offer only one usage, but the power PD applications must be able to adapt to both. The standard requires that the power supply is typically 48V, 13W ´s . PD device provides 48V to low voltage conversion is relatively easy, but at the same time should be insulated 1500V safety voltage .
        Third, the parameters
        A complete system consists of POE power supply terminal equipment (PSE, Power Sourcing Equipment) and the receiving end device (PD, Powered Device) in two parts. PSE device is an Ethernet client device powered devices , but also the entire process of POE Power over Ethernet managers . The PD device is receiving power PSE load , ie POE system client devices such as IP phones , network surveillance camera, AP and Pocket PC (PDA) or mobile phone chargers and many other Ethernet devices ( Actually, any power no more than 13W of equipment can be obtained from the corresponding RJ45 socket electricity ) . Both established based on the IEEE 802.3af standard equipment on the PD receiving end connectivity , device type, power level and other information links and on this basis PSE via Ethernet to the PD.
        POE standard power supply system of the main parameters are:
        1 between 44 ~ 57V voltage , typically 48V.
        (2) to allow maximum current of 550mA, the maximum starting current of 500mA.
        3 Typical operating current is 10 ~ 350mA, overload detection current 350 ~ 500mA.
        4 in the no-load conditions, the maximum required current 5mA.
        5 for PD devices 3.84 ~ 12.95W three levels of electric power request , the maximum does not exceed 13W. ( Note that 0 PD classification and grading of 4 does not show up and should not be used . )
        Fourth, the work process
        When arranged in a network PSE power supply terminal devices , POE Power over Ethernet working process is as follows.
        1 detects a start , PSE small device in the port output voltage until it detects a connection to a cable terminal supports standard IEEE 802.3af Powered Device .
        2. PD terminal equipment classification
        When the device detects the receiving end after PD , PSE device may be classified as PD devices , and equipment required for evaluating this PD power loss .
        3 Begin supply
        In a configurable time ( generally less than 15μs) startup period , PSE device starts from a low voltage power supply to the PD device up to provide 48V DC power supply.
        4 Power supply
        Equipment for the PD to provide a stable and reliable 48V DC , to meet the PD device does not cross 15.4W power consumption.
        5 off
        If the PD is disconnected from the network , PSE will quickly ( generally within 300 ~ 400ms ) stopping power for the PD device and repeat the detection process to detect the cable terminal is connected PD devices .
        Fifth, the power supply method
        Ethernet PoE standard for the use of DC power transmission cable to the POE compatible transport equipment defines two methods :
        Midspan France (Mid-Span)
        Use an Ethernet cable is not being used spare pairs to transmit direct current, used in general between the switch and the network terminal equipment , through the network cable to the network terminal equipment supply , Midspan PSE ( midspan power supply equipment ) is a dedicated power management equipment, and switches are usually put together. It corresponds to each port has two RJ45 jacks , one with a short connection to the switch , and the other to connect the remote device.
        End of the cross- connection (End-Span)
        Is used for the transmission of data transmit both the core current, the Ethernet data transmission using the different frequency signals . Corresponding Endpoint PSE ( end -powered devices ) that support POE function of Ethernet switches, routers, hubs , or other network switching equipment . Can foresee End-Span will quickly be promoted , which is due to Ethernet data transmission using common line pairs, thus eliminating the need to set up a dedicated independent power transmission line , which is only 8-core cables and matching standard RJ- 45 jack is of particular significance .

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