Hi,
I'm working on a design which is supplied from an external DC power source. I'm routing the supply (+ and -)via a common mode choke, so there's conceptually a separate DC ground either side of the choke (at least from a CM a.c. perspective).
The board also has a few RS232 ports and digital I/O lines, (each of which is fed through 3 terminal capacitors). These 'external' IO lines are presented on a connector.
My feeling is that any DC ground that I should make available on the external connector should be taken from *before* the common mode choke, since if it was the 'filtered' DC ground that was made available externally, the filter itself would get shunted if 'external' grounds were commoned.
_________ DC in + | | DC in + (Filtered)
----- | CM |----- DC in - |Choke | DC in - (Filtered)
----- | |----- | _________ | | _| Ground connection to ext.connector
I'm curious to know what the perceived wisdom is in this case? - Does this sound reasonable?
Many thanks
David