PoE mechanism of an S series switch

PoE mechanism of S series switches:

Power over Ethernet (PoE) is a remote power supply function. With this function, a device can provide power to powered devices (PDs) connected to its Ethernet electrical interfaces over twisted pair cables. PoE is reliable and standard and requires simple connections.

Note: A PC connected to a PoE-enabled interface will not be affected or burned because the following PoE detection process is performed:

1. Detect PDs. A power sourcing equipment (PSE) periodically transmits a low voltage with limited current through its ports to detect PDs. If the PSE detects a resistance with a specified value, PDs that comply with IEEE 802.3af or IEEE 802.3at are connected to the other ends of cables.
2. Negotiate power supply. A PSE classifies PDs and negotiates the power with PDs. Power supply capabilities can be negotiated by resolving detected resistances or the LLDP protocol.
3. Start to provide power. During the startup period (less than 15 ?s generally), the PSE starts to provide power to PDs from a low voltage and increases the voltage until the voltage reaches 48 V DC.
4. Provide power normally. Finally, the output voltage provided to PDs is stabilized at 48 V DC, and the power consumption of each PD does not exceed 30 W.
5. Stop providing power. The PSE keeps detecting the input current of PDs while supplying power. When detecting that the current of a PD falls below the minimum value or increases sharply, the PSE stops supplying power to the PD and repeats PD detection. This situation occurs when a PD is disconnected from the PSE or encounters a power overload or short circuit, or its power consumption exceeds the power supply capacity of the PSE.

For details, see Tell You About PoE.

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