According to the POE power supply workflow (refer to POE Foundation), the PD terminal should have a signature circuit and a PD power consumption grading circuit (optional). Through the detection of PSE power supply equipment, a stable 48V power supply voltage can be obtained. However, in the general circuit, the voltage of 48V is too high, which requires a power converter to convert the voltage of 48V into an appropriate voltage. Therefore, the circuit of PD equipment will be composed of signature circuit, power consumption grading circuit and power conversion circuit.

A conductive loop composed of metal wires and electrical and electronic components is called a circuit.