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.