EMI Bites: How to Use Ground Earth Connection to Improve EMC/EMI
Just don't.
When I inquired about the presence of this earth safety wire on this power supply, the manufacturer responded with:
"Oh, no, this is not really for safety; this is actually to improve EMI. Without this, we could not pass EMC tests."
This tells me that many things in this design are not well understood, in particular parasitics.
The difficult part in understanding parasitics is that they are not designed in the schematics.
You need to have a 3D physics picture of your design in order to understand stray coupling of electromagnetic fields.
In the case of this picture, the wire here is simply a patch—perhaps even a dangerous one—that has been implemented simply because the principles of EMC/EMI design are not well integrated from the start of the design.
This is more common than we would like to think, and even for most renowned companies.
If we want to master EMI and design for first-pass EMC, we need to think fields, not electrons.
And despite what some people in the industry say, thinking in terms of fields becomes easier once you have the right fundamentals. And most importantly, many of the things that did not make sense when thinking in terms of electrons start to finally come together.
Avoid these types of quick-and-dirty engineering. Design from first principles and design products to last and outperform.
To electromagnetic enlightenment,
–Dario
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