Step One: Detect PD
Firstly, the PSE will send a test voltage to the on-grid device to detect a 24.9k Ω common mode resistor in the receiving device. The test signal starts at 2.5V and then increases to 10V, which will help compensate for the loss of impedance caused by the Cat-5 cable itself, as this type of cable can reach a maximum length of 100m. If the PSE detects an appropriate impedance feature (24.9k Ω) from the PD, it will continue to increase the voltage. If the characteristic impedance is not detected, the PSE will not power up the cable. The Zener diode in the receiving device (PD) circuit ensures that the rest of the system is not affected by the test signal.
Step Two: PD end device classification
After detecting the receiving end device PD, the PSE will apply a voltage of 15-20V to the PD and determine the specific level of PD by measuring the current magnitude. If no other graded circuit is detected except for the first level resistance, the device is defined as zero level. At this stage, the power part of the PD will be maintained in a passive state by the Under Voltage Lockout (UVLO) circuit to isolate the switch stage until the feature and classification stages are completed.
Step Three: Power supply to PD
After the grading is completed, within a configurable time (usually less than 15 μ s) During the startup period, the PSE equipment began to operate from low voltage to PD equipment as follows:
Start power supply
Until a 48V DC power supply is provided.
Stable power supply
Provide stable and reliable 48V DC power for PD equipment.
Power outage
If the PD device is disconnected from the network, the PSE will quickly (usually within 300-400ms) stop supplying power to the PD device and repeat the detection process to detect whether the cable terminal is connected to the PD device.