POE+ SERIES SWITCHESTECHNICAL WHITE PAPER
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PoE Advantages:
Reliability: centralized power supply, convenient backup.
Simple connection: the network terminal does not need external power supply, only needs a network cable.
Standard: it conforms to IEEE 802.3af standard and IEEE 802.3at standard, and uses a global unified power interface, which can ensure the
interaction with PD of different manufacturers.
1.2 Power Supply Process on PoE Equipment
The steps to achieve PoE power supply are as follows:
1. Detection of PD: the small voltage limited by the periodic output current of PSE at the port is used to detect the presence of PD equipment. If
a resistance with a specific resistance value is detected, the cable terminal is connected to the receiving terminal equipment supporting IEEE
802.3af standard or IEEE 802.3at standard.
2. Power Supply Capacity Negotiation: PSE classifies PD and negotiates power supply. There are two ways to negotiate the power supply
capacity: analyzing the specific resistance detected and negotiating the power supply capacity through lldp protocol.
3. Start Power Supply: during the start-up period (generally less than 15 μs), PSE equipment starts to supply power from low voltage to PD
equipment until providing 48V DC voltage.
4. Normal Power Supply: after the voltage reaches 48V, PSE provides stable and reliable 48V DC power for PD equipment. When PSE equipment
only supports PoE and PoE+, the power consumption of PD equipment shall not exceed 30W.
5. Power Off: during the power supply process, PSE will continuously monitor the PD current input. When the PD current consumption drops
below the minimum value, or the current surges, such as unplugging the equipment or encountering PD equipment power consumption
overload, short circuit, power supply load exceeding PSE, PSE will disconnect the power supply and repeat the test process.
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