Using MAX4891 to switch ethernet without transformers

[zainka]

Hi

Would it be possible to switch Ethernet links using max4891 by connecting each Rj45 directly to the switch without having an transformer inn-between?
I have illustrated it below. Here there is only one max4891, but I might use up to three switches in a path between several rj45's to switch the lines between different equipment.


Look mama, No TRANSFORMERS!

 

[betwixt]

Ethernet links should not have any electrical conduction paths between them, all the signal coupling is magnetic through the transformers. As long as you respect that, you can use the first circuit and maybe even omit the common transformer (on the right side of the schematic) depending on what else is connected to the switch.

The second schematic might work but it violates ethernet rules and would be very prone to voltage differences between the connected devices.

Brian.

 

[zainka]

Thanks, I appreciate your fast response.

I have been informed now that the second schematic works but only in a closed controlled network with no connection to the internet, It has been done earlier, but this network was also limited to just a few nodes. Not in an Ethernet network as we are used to think of it. So will also be the case for where we want to use this device too but we will have more nodes than what was the case for the example I was shown.

Where the suggestion was to avoid transformers for simplicity I found that to be a bit insecure, hence my question, especially since the datasheet specifies the usage of transformers but I do believe that the max4891 can handle it without as long as there are no differences in potentials between the connected devices. I have earlier used it to switch video with great success and off-course ere we used no transformers.

I think your advice is a good one. I will discuss it further with my team and see if there could be any problems.

 

[FlapJack]

In a controlled environment with all equipment plugged in to the same outlet it may work. But even so it would be susceptible to ground loops.