ethernet transformers really needed ??

[evilheart]

i am working on an ethernet project , and the cost must be minimized as possible , i have seen circuits schematics for the chip i am using :
microchip ENC624J600

i have found schematics using magnetics and others without magnetics , magnetics chips are usually expensive , and in term of production i can't just add 2$ or 3 $ to the cost/unit , also cheaper alternative integrated magnetic connectors are not available that much in my country ,

can i neglect using the magnetics at all ?? i know it's important for filtering and isolation , but my application doesn't need high speed , and won't communicate that much , so i don't want to add to the cost just to increase the connection reliability from 90% to 99.99% , i may accept a bit lower reliability to decrease the cost

so according to your experiences , are the magentics really that essential ???

 

[BradtheRad]

This may not specifically apply to your question, but I seem to remember trying to use a plain inexpensive 8-line telephone coupler to connect two ethernet cables. It didn't work. I had to use the special ethernet coupler.

 

[pbernardi]

They are needed because there are no ground on Ethernet cables, just 4 diff pairs.

If you do not use a Ethernet transformer, the GND level of the signals may be in a different reference than your board and burn your system. If you ensure the signals are referenced on the same level (for example, in a backplane Ethernet), you may drop the transformer.

Google for transformerless Ethernet for more Info.