EMC filters that look right but don’t work
Hi Reader,
Have you ever built something that looked great in theory but failed in real testing?
EMC filters look easy. They are not.
Seeing them all around the Internet does not make them easy.
Today, you will learn how to avoid the common traps when building EMC filters
1️⃣ Designing them only for one kind of noise
There are two types of noise: common-mode noise and differential-mode noise. During the EMC tests, you measure the mix of both. The total amount of noise must be below a limit. Then, filters need to be effective for both types of noise.
2️⃣ Considering only nominal values
Filters are made of components like inductors (L) and capacitors (C). When we start designing them, we use the nominal values to get a rough idea. Once the functionality is validated, we need to consider the real behaviour of components:
Temperature derating
Voltage and current derating
Saturation
Tolerances
Start with one effect and add the rest, one at a time.
3️⃣ Ignoring the grounding
Filters need a connection to the metallic case, to remove common-mode noise. It is easy to make the connection in a careless manner and ignore the consequences of having too much extra inductance there.
To design effective EMC filters:
1️⃣ Design filters for common-mode and differential-mode noise
2️⃣ Consider component non-ideal behaviours
3️⃣ Take care of the grounding
EMC Academy in Oxford
If you like discounts like I do, here is a 30% discount for the EMC and CI in Oxford
EMCCI25
📍St Anne’s College, Oxford
📅 19th - 21st May 2025
What will you get?
Learn from the best of the best in the EMC Academy:
Daniel Beeker, Billion Dollar Mistake: wrong perspective on designing systems
Rod Macpherson, PCB Design considerations for optimal EMC Considerations
Dr Marco Klingler, Mastering EMC Through Hands-On Numerical Simulation
James Pawson, Radiated Emissions Essentials
Keith Armstrong, PCB and Cable Shield Grounding
Dr Min Zhang, The art of EMI troubleshooting
I am flattered to have the chance to give a talk this year!
From the block diagram to the laboratory: How to prepare for a successful EMC test campaign
Will you attend? Hit reply and let’s have a coffee together!