What is a PoE controller?Power Over Ethernet controllers (PoE controller) are a device for controlling the power supply of equipment over Ethernet cables while still maintaining Ethernet capability in accord with IEEE 802.3af-2003 and IEEE 802at-2009. IEEE 802.3af provides 15.4W of DC power and IEEE 802.3at delivers 25.5W. PoE systems have two types of equipment to consider. Power sourcing equipment (PSE) refers to the devices that obtain their power supply from a source other than the Ethernet. Powered devices (PDs) get their power from the Ethernet interface. There are other proprietary standards that can support 90W or more.Ethernet cable contains two pairs of wires for differential signaling of data. Ethernet is a differential signaling standard with an encoding scheme that eliminates DC offsets. This allows DC power to be sent on each pair. PoE controllers provide switch-mode power supply capability to PDs by using a DC voltage input derived from the Ethernet (which can be 37-57V).Power Over Ethernet DesignThe PoE controllers can usually detect what type of supply is present on the Ethernet cable, and go through a power up sequence. The PSE detects the signature resistance of a PD load on the cable of 19-25.5kOhm. The PoE controller can switch this load into the circuit with a dedicated port. It signals IEEE 802.3at capable by the PD presenting a 0.25-4mA load under 7-10V (for Mark 1) or 14.5-20.5V (for Mark 2) from the PSE. The PSE outputs a start-up voltage higher than 42V, which causes the PoE controller to start up the PD power supply. It does this by signaling on its power good dedicated output signal port.PoE controllers are used in applications like access points, VoIP phones, RFID reader systems and security cameras. They usually have high ESD protection, thermal protection and may have capability to control or indicate for the use of an auxiliary power supply for when the Ethernet is not powering the device. 더 읽기 읽기 안 함