EMC Basics: Clamp-on Ferrites

Welcome to the fifth and final installment of our comprehensive blog series on EMC basics!

In the previous posts, we walked you through an overview of EMC, chip bead ferrites, losses, and common mode vs. differential noise.

Today, we will talk about using clamp-on ferrites to combat unwanted noise. We’ll finish with a discussion about why it’s so important to design with EMC in mind.

Common Mode Chokes and Clamp-on Ferrites

Taking what we learned about common mode chokes in the previous post, let's apply that to clamp-on ferrites.

Clamp-on ferrites are typically used for common mode filters. A single cable goes through the ferrite, but the cable includes two wires (Vcc and ground).

You can also use clamp-on ferrites for a differential mode noise, but now you have to separate the two lines in the cable so that you have a single wire going through the ferrite. So the type of clamp-on ferrite you choose will depend upon your intended use (whether for a common mode or a differential mode filter).

Adding Turns Through the Ferrite

Our clamp-on ferrites from Wurth Electronics Midcom are made from two different materials: manganese zinc and nickel zinc. The blue lines that you see here represent the nickel zinc part.

Now, we're going to discuss adding turns through the ferrite. By adding multiple turns through the ferrite, you increase the impedance. You see the peaks going up, but you're also shifting the frequency range because you're adding capacitance.

So the thicker lines represent the second and third turns. Again, you're seeing the impedances increasing — however, the frequency is shifting.

The red lines represent the same example but with manganese zinc. Notice now that when we add the turns with manganese zinc, the impedance does increase, but the frequency does not shift dramatically. That's because manganese zinc is a much narrower bandwidth material.

Types of Clamp-on Ferrites from Wurth Electronics Midcom

This image shows three different types of clamp-on ferrites we offer at Wurth Electronics Midcom.

The STAR-FIX-LFS, or low-frequency suppression, is made of manganese zinc. Thus, it is used for low-frequency noise attenuation.

The STAR-TEC, the STAR-RING, and the STAR-FIX are all made of nickel zinc. These are used to attenuate noise at the higher frequencies.

And then there’s the STAR-GAP, which is aimed at noise above 100MHz and up to 2.5GHz.

The Importance of Designing with EMC in Mind

Hopefully, by this point of the blog series, you've gained an appreciation for designing your products with EMI in mind.

If you don't design your product with EMI in mind, you can find yourself spending thousands of dollars per visit to the EMC Lab trying to fix your problem. Even worse, you can find yourself being fined hundreds of thousands of dollars because you're not complying with the EMC regulations required by your industry.

The point we're trying to drive home with this blog series is that by using relatively inexpensive EMC components at the beginning of your design, you can reap major cost savings by the time you ultimately get your product to production.

It’s a small concept to learn, but the benefits are huge.

And that wraps up our blog series on EMC basics!

Beyond what we have shown you in this EMC blog series, we also have several tools on our website and in our catalog to help you choose the proper component for your application. We also have direct salespeople and FAEs located all over the world who would be happy to come visit you in person.

If you have any questions — about our EMC products or anything else — feel free to contact us!