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

📅 19^th - 21^st 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!

​

​