Shielded vs. Unshielded Inductors for SMPS

Welcome back to our blog series on filter design for switched-mode power supply (SMPS)!

In the final installment of our four-part series (read the first three posts here), Lorandt Fölkel M.Eng will explain the difference between shielded and unshielded inductors and provide resources for learning more about SMPS.

The Difference Between Shielded and Unshielded Inductors

So, what is the big difference between shielded and unshielded inductors?

First of all, unshielded inductors have a bobbin core. If you were to cut into it, you would see that the magnetic field goes out with an infinite gap.

However, if you were to add a shielded ring to the inductor, you would see that the magnetic field turns back to the core. There is some magnetic leakage at the top and the bottom, but it is much more manageable than the leakage of unshielded inductors.

For example, we once had a customer who had a small DC/DC converter and was experiencing problems with passing the required conducted emission levels at the EMC lab. By simply changing to a shielded inductor and adding a ground plane to his PCB, the customer’s noise levels dropped drastically. When the guy at the EMC lab saw the change, he actually thought that his machine wasn’t working!

Words of Caution Regarding Magnetic Fields

When dealing with magnetic fields, it’s always better to be safe than sorry.

Be sure to select the right parts for your application. Don’t just look at the cost. In fact, sometimes the best solution is also the easiest — and the most cost-effective.

The Trilogy of Magnetics

At Wurth Electronics, we have plenty of resources available to help you with understanding magnetics for SMPS (and electronics and electromagnetics in general).

Our best resource is the Trilogy of Magnetics, a design guide specifically for EMI filter design, SMPS, and RF circuits. You’ll love this helpful, how-to book!

You can also check out our whole suite of design guides at Wurth Electronics:

Still Have Questions about SMPS?

If you can’t find the answers you’re looking for in any of the above guides — or if, let’s face it, you just want some help pronto — don’t give up. Just give us a call!

Our technical experts are always on hand to answer your questions and provide feedback on your design. While our global headquarters is in Germany, we have offices and factories all around the world, and we’re able to distribute even farther.

You can reach us via any of the following methods:

  • +49 7942-945-0
  • +1 605 886 4385
  • eisos@we-online.de

...Or by contacting your local representative!