powered device (PoE) (PD)
A Powered Device(PD) is an end device that is supplied with power via the Ethernet. In these technologies, which are dealt with in the IEEE 802.3af, 802 .3at and 802.3bt working groups and are listed under Power over Ethernet( PoE), PoE+ and PoE++, the powered devices are connected in a star configuration to a power sourcing equipment( PSE). The powered devices (PD) can be VoIP phones, webcams, or wireless access points( WAP).
Depending on the connector used, there are four or eight connection lines between the power sourcing equipment and the powered device (PD) for the data and power supply. For 802.3af, the standardization groups have standardized extraction powers of 4.0 W, 7.0 W and 15.4 W, for 802.3at it is 25.5 W, and for 802.3bt it is 45 W, 60 W, 75 W and 90 W. The supply voltages, which can range from 36 V to 57 V, are regulated down to the corresponding operating voltages in the powered devices via DC/DC converters.
A power sourcing equipment identifies a Powered Device by a certain signature resistance specified by IEEE. This process is called resistive power discovery. Only when the resistive conditions are met does the line connection between the two components take place. The Powered Device must classify itself to the Power Sourcing Equipment (PSE) with the PD classification. If a PSE unit has detected a Powered Device, then it performs a power classification so that the power limits are not exceeded.
The PD classification was made by IEEE 802.3bt and includes eight classes with the class division PD class 1 to 8. For the supply, there are two modes of operation: phantom supply and spare pair supply. Powered devices must support both supply modes.