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Why to use isolated POE, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Recently, some projects need to use POE and Power over Ethernet, so they naturally face a question: whether to use isolated POE or non-isolated POE? (we are talking about standard POE here, but non-standard POE is not under discussion.)

The main difference between isolated POE and non-isolated POE is that isolating POE needs to use transformers and Optocoupler switches and other devices, the circuit is more complex, non-isolated POE can use inductors. Therefore, the isolation POE circuit is more complex and more expensive, as illustrated by the example of SI3402 in the following figure.

Since chip manufacturers have introduced two connection methods, that is, both will be used. Although isolating POE is more complex and costly, it naturally has its own advantages.

Among them, a big problem of non-isolated POE is that it will cause the fault of circuit without power supply under certain circumstances. When the non-isolation module is used with the PoE switch, several PoE switch ports do not have power supply, and it is good and bad. So why is that?

PSE supplied POE with the following electrogram:

According to the POE standard, PSE adopts the way of positive electrode connected with GND, and controls the power supply by controlling the negative switch. When a PD device is detected in a network port on the PSE side, the switch K will be turned on to power the PD device in this port, while the switch will not be turned on if there is no PD device access in other ports.

If the outer shell of the PD is metal and is connected to the GND on the board and the earth, then it may cause the problem of no power supply. The reasons are as follows:

When multiple GND-connected non-isolated PD products are connected, their negative electrodes are all connected together, so that the power supply current does not necessarily flow back from their respective network ports, but may flow back from one port, as shown by the red arrow in the image above, which will cause large currents to be detected at the PSE1 end and disconnect the power supply due to overload.

If it is an isolated POE, the current i1 can only flow back from port 1, the current i2 is flowing back from port 2, and the current in can only flow back from port n. This problem does not exist.

Therefore, if the PD terminal power supply negative grounding (shell grounding) products, it is necessary to use isolated POE. In addition, the isolated POE is certainly better at protection than the non-isolated one. After all, the network cable is very long and easy to be disturbed, especially outdoor products, which will be struck by lightning and so on. Isolation can serve as an extra layer of protection.

So try to use isolated POE.

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