New power supply - POE power supply

New power supply - POE power supply
POE (Power Over Ethernet) refers to the technology that can provide DC power to some IP-based terminals (such as IP phones, wireless LAN access points AP, network cameras, etc.) while transmitting data signals without making any changes to the existing Ethernet Cat.5 wiring infrastructure. POE technology can ensure the normal operation of the existing network while ensuring the safety of the existing structured wiring, minimizing costs.

POE is also known as the power supply system based on the local area network (POL, Power over LAN) or Active Ethernet (Active Ethernet), sometimes referred to as Ethernet power supply. This is the latest standard specification for transmitting data and electrical power simultaneously using the existing standard Ethernet transmission cable, and maintains compatibility with existing Ethernet systems and users. The IEEE 802.3af standard is a new standard based on the Ethernet power supply system POE. It adds relevant standards for direct power supply through network cables on the basis of IEEE 802.3. It is an extension of the existing Ethernet standard and the first international standard for power distribution.

IEEE started to develop the standard in 1999, and the earliest participating manufacturers were 3Com, Intel, PowerDsine, Nortel, Mitel and National Semiconductor. However, the shortcomings of the standard have been restricting the expansion of the market. It was not until June 2003 that IEEE approved the 802.3af standard, which clearly defines the power detection and control matters in remote systems, and stipulates the way routers, switches and hubs supply power to devices such as IP phones, security systems and wireless LAN access points through Ethernet cables. The development of IEEE 802.3af includes the efforts of many company experts, which also allows the standard to be tested in various aspects.

A typical Ethernet power supply system. Keep the Ethernet switch equipment in the wiring cabinet, and use a powered hub (Midspan HUB) to provide power to the twisted pair of the LAN. At the end of the twisted pair, the power is used to drive phones, wireless access points, cameras and other devices. To avoid power outages, a UPS can be selected.

POE system composition and power supply characteristic parameters

A complete POE system consists of two parts: power supply equipment (PSE) and power receiving equipment (PD). PSE equipment is a device that supplies power to Ethernet client devices and is also the manager of the entire POE Ethernet power supply process. The PD device is the PSE load that receives power, that is, the client device of the POE system, such as IP phones, network security cameras, APs, PDAs or mobile phone chargers and many other Ethernet devices (in fact, any device with a power of no more than 13W can obtain the corresponding power from the RJ45 socket). The two establish information about the connection status, device type, power consumption level, etc. of the power receiving device PD based on the IEEE 802.3af standard, and based on this, the PSE supplies power to the PD through Ethernet. The

main power supply characteristic parameters of the POE standard power supply system are:
1. The voltage is between 44 and 57V, with a typical value of 48V.
2. The maximum allowable current is 550mA and the maximum starting current is 500mA.
3. The typical operating current is 10-350mA, and the overload detection current is 350-500mA.
4. Under no-load conditions, the maximum required current is 5mA.
5. Provide PD devices with five levels of power requests from 3.84 to 12.95W, with a maximum of no more than 13W.
2. Working process of POE power supply

When a PSE power supply device is deployed in a network, the working process of POE Ethernet power supply is as follows.
1. Detection: At the beginning, the PSE device outputs a very small voltage at the port until it detects that the connection at the cable terminal is a powered device that supports the IEEE 802.3af standard.
2. PD device classification: After detecting the powered device PD, the PSE device may classify the PD device and evaluate the power loss required by the PD device.
3. Start power supply: During a configurable startup period (generally less than 15μs), the PSE device starts to supply power to the PD device from a low voltage until a 48V DC power supply is provided.
4. Power supply: Provide PD devices with stable and reliable 48V DC power to meet the power consumption of PD devices not exceeding 15.4W.
5. Power off: If the PD device is disconnected from the network, the PSE will quickly (generally within 300-400ms) stop powering the PD device and repeat the detection process to detect whether the terminal of the cable is connected to the PD device.

3. The principle of POE power supply through cable The

standard Category 5 network cable has four pairs of twisted pairs, but only two pairs are used in 10M BASE-T and 100M BASE-T. IEEE80 2.3af allows two usages. When the idle pin is used for power supply, pins 4 and 5 are connected as positive poles, and pins 7 and 8 are connected as negative poles. When
the data pin is used for power supply, the DC power supply is added to the midpoint of the transmission transformer, which does not affect the data transmission. In this way, line pairs 1 and 2 and line pairs 3 and 6 can have any polarity.
The standard does not allow the above two situations to be applied at the same time. The power supply equipment PSE can only provide one usage, but the power application equipment PD must be able to adapt to two situations at the same time. The standard stipulates that the power supply is usually 48V, 13W. It is easier for the PD device to provide 48V to low voltage conversion, but at the same time, there should be an insulation safety voltage of 1500V.

Two power supply methods of POE

The POE standard defines two methods for using Ethernet transmission cables to transmit DC power to POE-compatible devices: one is called "Mid-Span", which uses the unused idle wire pairs in the Ethernet cable to transmit DC power, and the corresponding Endpoint PSE supports POE-functional Ethernet switches, routers, hubs or other network switching devices. The other method is "End-Span", which transmits DC power simultaneously on the core wire used for data transmission, and its power transmission uses a frequency different from that of the Ethernet data signal. Midspan PSE is a special power management device, usually placed together with the switch. It has two RJ45 jacks for each port, one connected to the switch with a short line, and the other connected to the remote device. It is foreseeable that End-Span will be rapidly promoted. This is because Ethernet data and power transmission use common wire pairs, thus eliminating the need to set up dedicated wires for independent power transmission, which is particularly important for cables with only 8 cores and matching standard RJ-45 sockets.

Development: PowerDsine, a manufacturer of Ethernet power supply chips, will hold an IEEE meeting to formally submit the "High Power Ethernet Power Supply" standard, which will support power supply for devices such as laptops. PowerDsine will submit a white paper suggesting that the 48v input and 13w available power limit of the 802.3af standard be doubled. In addition to laptops, the new standard may also power LCD monitors and video phones.


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sp; 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 PD devices with five levels of power requests from 3.84 to 12.95W, with a maximum of no more than 13W.
2. POE power supply working process

When a PSE power supply device is deployed in a network, the POE Ethernet power supply working process is as follows.
1. Detection: At the beginning, the PSE device outputs a very small voltage at the port until it detects that the connection at the cable terminal is a powered device that supports the IEEE 802.3af standard.
2. &nData download: [New power supply - POE power supply]