App note: PoE Powered Device (PD) rectifier bridge circuits

App note from ON Semiconductors regarding different bridge rectifier topologies and how to reduce power losses in these stages. Link here (PDF)

Power over Ethernet (PoE) is a technology which allows power sourcing equipment (PSE) to safely transfer power to a powered device (PD) through an Ethernet cable.

The majority of the power transferred to the PD normally goes to a DC−DC converter to supply loads such as a camera or an IP phone. However, not all the power delivered at the PSE output will be available to this load, due to a number of reasons. First of all, power loss occurs due to the resistance of the Ethernet cable. Additionally, the combined efficiency of the PD’s bridge rectifier and DC−DC converter is typically around 90%. It is important to keep in mind that the power is limited in a PoE system. When designing a powered device, reducing the power loss in the rectification and conversion stage means more power is available to the loads.

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