The newly approved IEEE802.3af standard enables the simultaneous transmission of DC power and data over Ethernet networks. With an available power supply of approximately 13W, many devices can now be powered directly through their Ethernet connections, eliminating the need for wall AC adapters. Devices that can be powered via Ethernet include digital VoIP phones, network wireless access points, PDA charging stations, HVAC thermostats, and other low-power data devices connected to Ethernet outlets.
As Ethernet power delivery continues to evolve, security measures are becoming increasingly important to protect regular PCs and laptops from potential damage caused by the 48V voltage levels involved in PoE (Power over Ethernet).
Ethernet cable power supply involves the use of a PSE (Power Sourcing Equipment) to deliver a regulated 48V through either the signal pair or an alternate pair of wires. This power is transmitted as a common-mode voltage difference between the two pairs. The power supply is coupled to the cable through the center tap of the isolation transformer, which allows differential signals to pass through without affecting data transmission. The 48V potential difference between the transmitting and receiving pairs does not interfere with the data flow at the receiving end.
A PSE can also act as a current-limiting device, ensuring safe operation. Meanwhile, PD (Powered Device) detection, precise PD classification, current limiting, and disconnection detection typically require a separate circuit independent of the 48V power switching mechanism. Therefore, specialized circuits have been developed to meet the stringent demands and robustness required for high-voltage power switching applications.
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