PoE switch power supply process
PoE switch power supply process
Detection: first PSE will send a test voltage to the network device to detect a 24.9k common mode resistance in the receiving device. The test signal starts at 2.5V and then increases to 10V, which will help compensate for the loss caused by the self impedance of the Cat-5 cable. Because the cable up to 100m. If the PSE detects an appropriate impedance characteristic (24.9k) from the PD, it will continue to raise the voltage. If the characteristic impedance is not detected, the PSE will not power the cable. Will ensure the rest of the system is not affected by the interference test signal of electric equipment in the circuit of Zener diode.
PD device classification: when the PD is detected, the PSE will be applied to the PD 15 to 20V voltage, and by measuring the current size to determine the specific level of PD. If the first level of resistance is detected, no other grading circuit is found, which is defined as a zero level. In this phase, the power supply section of the PD will be held in a passive state by the undervoltage lockout (UVLO) circuit in order to isolate the switch level until the characteristics and stages are completed.
Starting power supply: after the completion of the grading, in a configurable time (typically less than 15 s) during the start-up period, PSE devices start from low voltage to PD devices
A) power supply until the supply of 48V DC power supply.
B power supply: PD equipment to provide a stable and reliable 48V DC, to meet the PD equipment does not exceed the power consumption of 12.95W.
C (power off): if the PD device is disconnected from the network, PSE will quickly (usually within 300 ~ 400ms) to stop the supply of PD equipment, and repeat the detection process to detect whether the cable terminal is connected to the PD device.
When connecting any network device to the PSE, the PSE must first check whether the device is PD, so as not to give the PoE standard does not meet the Ethernet device to provide current, because it may cause damage. This check is performed by providing a small current limited voltage to the cable to check whether the far end has a desired characteristic resistance. The full 48V voltage is provided only when the resistor is detected, but the current is still limited, so that the terminal device is in the wrong state.
As an extension of the discovery process, the PD can also be used to classify the power supply requirements of PSE, which will help PSE to provide power in an efficient manner. Once the PSE starts to provide power, it will continuously monitor the PD current input, when PD current consumption dropped to the lowest value, such as in unplug or encountered PD equipment power consumption power supply load, overload and short circuit over PSE, PSE will disconnect the power and start the test again.
Poe switch professional manufacturer - Hong Ruiguangxiang