On the other hand, setup A (secondary and primary grounds connected) should be avoided as that would eliminate the galvanic isolation provided by the transformer
Thanks, i apologise for my poor drawing......that link in "A" doesnt connect pri and sec gnds...it connects earth to secondary GND.
Unless there is a compelling reason I usually go with one connection only at the mains connector and everything tied there.
Thanks,
So by this do you mean you prefer “A”?
Or do you literally mean that you would take a wire from secondary ground right back to the earth place at the mains input connector , where earth connects to chassis?
As you know, a lot of comms lines connect to devices which use Earth as ground, and so you often need to earth your secondary because of this. As you know, connecting the secondary of an offline SMPS to earth always means poorer EMC performance, though it just needs to be tolerated for various reasons.
As you know, when the secondary ground of an offline SMPS is connected to earth ground, then we have earthed one side of the “common mode antenna”….which makes radiated emissions far worse.
As you know, its common to earth the secondary of an offline SMPS, otherwise if left floating it may float up to some random potential…often mains peak.
But which of "A" and "B" in the top post gives worse EMC performance?