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The principle of POE power supply and its power supply process
Sep 05, 2017

Initially, the PSE device outputs a very small voltage at the port until it detects that the cable terminal is connected to a receiving terminal that supports the IEEE 802.3af standard.

2. PD device classification

When the receiving terminal device PD is detected, 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 time (typically less than 15μs), the PSE device begins to supply power from the low voltage to the PD device until a 48V DC power supply is provided.

4. Power supply

For the PD device to provide a stable and reliable 48V DC power to meet the PD device does not exceed 15.4W power consumption.

5. Power off

If the PD is disconnected from the network, the PSE will quickly power the PD device (typically within 300 to 400 ms) and repeat the detection process to detect if the terminal of the cable is connected to the PD.

6. Power supply method

The POE standard defines two methods for transmitting direct current to a POE-compliant device using an Ethernet transmission cable:

Mid -Span

The use of idle cable pairs that are not used in the Ethernet cable to transmit DC power between the switch and the network terminal equipment can be used to power the network terminal equipment through the network cable. The Midspan PSE is a dedicated power management Equipment, usually put together with the switch. It corresponds to each port has two RJ45 jack, one with a short-term connection to the switch, the other connected to the remote device.

power over ethernet.png


It is the transmission of data used in the core line at the same time transmission of direct current, the transmission and Ethernet data using a different frequency. The corresponding Endpoint PSE (end-powered device) has POE-enabled Ethernet switches, routers, hubs, or other network switching devices. It is envisioned that End-Span will be rapidly promoted, due to the fact that Ethernet data and transmission use common line pairs, thus eliminating the need for independent transmission of dedicated lines, which only 8-core cable and matching standard RJ- 45 socket significance is particularly important.

power over ethernet poe.png

6. Development

PowerDsine, an Ethernet-powered chip maker, will convene an IEEE conference to formally submit a "high-power Ethernet power" standard that will support powering equipment such as laptops. PowerDsine will submit a white paper, it is recommended to 802.3af standard 48v input, 13w available power limit increased by 1 times. In addition to notebook computers, the new standard is also possible for LCD monitors and video phones and other power supply.

October 30, 2009 IEEE out of a new 802.3at standard, which provides the POE can provide higher power, more than 13W, can reach 30W!