83#🚀 How to Design a Differential Mode Inductor for an EMI filter

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👋 Hello, friends! Dr. Molina here 👨‍🔧

Welcome to Dr.Molina Newsletter, where I break down Magnetic design for you every week, in 4 minutes the time needed.

Back in 2012, I was designing a Differential Mode Inductor (DM) for a three stages EMI filter. Actually, we did a publication about it.

Power distribution in a 13 kW Three-Phase Rectifier system: Impact on weight, volume, and efficiency

To design an EMI filter, the first step is to calculate the attenuation required to comply with your standard. An L-C filter (second-order filter) provides 40 dB/decade of attenuation; however, the Lab measurements will show you the attenuation limits due to component parasitics. Once the frequency grows, the attenuation decreases until one moment, when it will increase. This is why we need several stages of L-C filters because, with one single stage, we couldn´t achieve the attenuation required due to the parasitics.

In the design of this filter, I need three stages to get 120 dBuV of attenuation. With a capacitor of C=0,22uF, the inductor needed is L=120 uH.

I have to design the DM inductor with the following specs:

• Current: 5,8 Arms and 8 Apeak

• Grid Frequency 400 Hz

• Inductance at nominal power =120 uH

At that moment, I had an Excel file to help me in the iterative process. It took me some time to adjust the Excel every time. To be honest, if there is a mistake in the calculations, it could not be easy to detect.

Now, I have Frenetic Online. It took me 5 min (literally, to get the same result).

First, I add the waveform and the inductance.

I asked the system which is the best core; in this case, I just went to a specific one and asked. How many turns and which wire do I need? And the system provides the answer to me. As you can see, I can see the saturation curve :).

And I assure you these calculations are correct (unlike my Excel).

But the most important part is coming. You can ORDER A SAMPLE! Yeah!! You can receive a sample of your custom design.

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Mag & Mad 2023 Update

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Dates Confirmed

13th and 14th of September

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