Poe Power Supply Application Research _ Network

Study on the application of Poe power supply (I.)

Introduction to Guan Jinssong PMP 2010-4-2 Poe

POE refers to the transmission of data signals to some ip-based terminals (such as IP telephones, wireless LAN access point APS, network cameras, etc.) while the existing Ethernet CAT.5 cabling infrastructure is not changed Ethernet It can also provide DC-powered technology for such equipment. Poe technology can ensure the existing structure wiring security while ensuring the normal operation of the existing network, to minimize costs.

Poe is also known as a LAN based power supply (POL) or active Ethernet, sometimes referred to as Ethernet power, which is the latest standard specification for transmitting data and power while using existing standard Ethernet transmission cables, and maintains compatibility with existing Ethernet systems and users. The IEEE 802.3AF standard is the new standard for Poe based on the Ethernet power supply system, which, based on IEEE 802.3, adds the relevant standards for direct power through the network cable, is an extension of existing Ethernet standards and is the first international standard on power distribution.

IEEE began setting up the standard in 1999, with the earliest participants being 3Com, Intel, Powerdsine, Nortel, Mitel and National Semiconductor. However, the shortcomings of the standard have been restricting the expansion of the market. Until June 2003, IEEE approved the 802. 3AF Standard, it clearly stipulates the power detection and control matters in the remote system, and provides the way for the routers, switches and hubs to power the IP phone, the security system and the wireless LAN access point through the ethernet cable. The development of the IEEE 802.3AF encompasses the efforts of many corporate experts, which makes it possible to test the standards in all respects. By 2009 IEEE had a new 802.3AT standard, which stipulated that Poe could provide a higher power, a single output power exceeding 13W, and a theory of 50W. System composition and power supply characteristic parameters of Poe Poe Power system

A complete Poe system consists of a supply-side device (PSE, power Sourcing equipment) and a two-part device (PD, Power Device). The PSE device is the device that supplies the Ethernet client device and is also the manager of the entire Poe Ethernet power supply process. While PD devices are powered by the PSE load, the client devices of the Poe system, such as IP telephony, network security cameras, AP and Handheld computers (PDAs) or mobile phone chargers, and many other Ethernet devices (in fact, any device with a power not exceeding 13W can obtain the corresponding power from the RJ45 socket). Both are based on the IEEE 802.3AF standard to establish information about the connection, type of equipment, power level and so on of PD of the electric terminal device, and use this as the PSE to power the PD through Ethernet.

The main functions of PSE are as follows:

² Search Link node for PD.

² is powered by a link node for the detected PD.

² Monitor power Status through link nodes.

² when PD is not requested, power off and return to the search state.

The main power supply characteristic parameters of Poe standard power supply system are:

1. Voltage between 44~57v, the typical value is 48V.

2. Each pair of lines allows maximum current of 600mA.

3. Typical working current is 10~350ma, overload detection current is 350~500ma.

4. Under no-load conditions, the maximum required current is 5mA.

5. Provide 4~25.5w five-level electrical power requests for PD equipment, up to 30W max.

But theoretically, one of the important improvements in the 802.3AT specification is to set the upper limit of a pair of wire currents to 600mA. Now, PSE must be able to provide at least 600mA of current, a 50V minimum output voltage and 57V maximum output voltage. This translates to a 34.2W of PSE output power. The model design value of the cable resistor is not greater than 12.5 Ω, according to the 4.5W loss, thus generating the available power of 34.2w-4.5w= 29.7W on the PD connector. It is necessary to take into account the 48V conversion efficiency, there is 0.9W loss, so that the final transmission to the PD load of the available power of about 29.7 w-0.9w = 28.8W.

If the voltage is applied at the same time on two pairs of wires, and the two groups of 600mA currents are passed, the theoretical output power can reach 28.8W * 2 = 57.6W. Working process of Poe Power supply

When the PSE power supply device is deployed in a network, the Poe power supply operation process is shown below.

1. Detection: Initially, the PSE device outputs a very small voltage on the port until it detects a connection to the cable terminal as an electrically supported device that supports the IEEE 802.3at standard.

2. PD Terminal Equipment Classification: When the electrical terminal device PD is detected, the PSE device may classify PD devices and assess the power loss required for this PD device.

3. Start power: In a configurable time (typically less than 15μs), the PSE device starts to power the PD device from a low voltage until it provides a 48V DC power supply.

4. Power supply: For PD equipment to provide stable and reliable 48V DC power, to meet the PD equipment does not cross 15.4W power consumption.

5. Power off: If the PD device is disconnected from the network, PSE will quickly (generally within 300~400ms) stop powering the PD device and repeat the detection process to detect if the cable terminal is connected to the PD device.

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