Switched Mode Power Supply - EMI will catch you when you least expect it!
It's always about them: Common-mode current!
They always find a way to sneak in and catch you off guard.
Unless you are prepared, of course.
See, the thing about common-mode currents is that if you give them the choice to close the current loop, even if this is through parasitics, they will take it.
That's why preparing your PCB design for the Conductive Emissions test is one of the toughest parts of being a PCB Designer.
Yes, I said PCB designer because this is actually one of our duties.
Not sure if you didn't know, but your design will dictate the majority of the chance of passing the test.
The reason?
Well, the reason is always about the electromagnetic fields, in particular, the uncontained ones.
Especially those coming from the Switching transistor in your SMPS, or the rectifying diodes, or from any other devices which handle the conversion of energy.
Not just any conversion of energy, but the sharpest one.
The one that has the highest energy harmonic content.
So what is the tip here?
When you are preparing your PCB design, remember that PCB Design is not just about connections from point A to B, but is all about the fields, more in particular, the energy in the fields!
So what always helps me (and my clients) is to think in terms of fundamentals.
Fields, Currents, Impedance.
You will notice that things will change quite a bit when you start seeing PCB Design in this way, and you will start to see things that you couldn't see before.
Such is the case of the parasitic effects...
I hope this helps,
Dario
