Now, on a switching supply, you're supposed to have a Y-type cap between input and output commons, to shunt the RFI coupled across the transformer's interwinding capacitance (and maybe a common mode choke on input and/or output to improve that isolation with respect to the surroundings). But what should you do if the output side is also bouncing (different frequency, out of phase)?
Specifically, imagine a high side gate drive circuit powered by a DC-DC converter. The driver's "common" is bouncing at, let's say 320Vp-p, so it's not really "common" in any useful sense. What then? Should there be CM chokes anywhere, or would those only make things worse (e.g., resonating with the parasitic capacitances)?
Tim