Cause of conducted common mode noise in an smps?

[grizedale]

Hello,

In an offline SMPS, please can you confirm that conducted common mode noise is ONLY caused by signals which radiate out of the switching stage and return to the neutral wire at a point outside of the mains input connector.?

So, for common mode noise to occur, some signal must actually *radiate* out from the smps.?

...this must be the case, because current ALWAYS travels in loops, and so any noise that doesnt radiate will simply loop back and go back down the neutral wire....and thus NOT produce common mode noise.?

 

[dick_freebird]

Loop current ought to result in differential mode noise, but
not all current returns, some goes out the output, and the
imbalance might appear to have some common mode
component.

To the extent that AC ground current and input current
are in phase (likelier during edges than the quasi-DC
settled conduction periods) the noise will be put to
"common mode" category.

If input ground is your reference point and VIN has
a perturbation, is common mode noise then just half
the differential noise?

 

[yura717]

any electronic device has Johnson–Nyquist noise .....
Johnson