Electronics > Beginners

RS485 Ground isolation

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T3sl4co1l:
Even Ethernet is not perfectly free, as it has a 1.5kV limit and the isolation is galvanic, not RF (there's a 1nF to ground to knock down peak ESD voltage).  Obviously, a far sight better than RS-485, still. :)  The most truly differential is propagating EM waves, I suppose (confined to a fiber or waveguide, or otherwise)?

Yeah, RF bypass caps can help. :-+

Tim

Brutte:
The RS-485 signal is differential but only within common mode range. Typically +12V down to -7V with respect to GND pin of transceiver. If you exceed this range then it stops being differential. Just keep A and B within these limits. Of course the idea with third wire is ok.

What about a latched comparator that senses for +12V and -7V violations? That could be helpful in your development.

mikeselectricstuff:
For one-way comms, you can use passive-input isolators like IL610, which are truly differential and don't care about the common-mode voltage. Loading is quite high so only viable for niche applications, but can be very useful.

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