This type of curve is typical for many ferrites. frequency for these materials to determine shielding effectiveness. However, make sure to check the value of μ vs. They also provide suppression of radiated EMI, acting as a standard shielding material. These materials can provide shielding against inductively coupled noise originating from a high dI/dt source, such as you would get in a high current switching power regulator. A common application is in power electronics to counteract switching noise without adding a filter circuit to a layout. These components are literally plates or disks of a ferrimagnetic material, and they are placed in an enclosure near an offending component. Common-mode and differential-mode noise impedance values in a two-terminal ferrite chip. The common-mode impedance shows the typical behavior of a single-ended inductor, but the differential-mode component still has high impedance, limiting the use of this type of component as a differential-mode filter unless you’re worried about filtering up to ~GHz frequencies. For example, take a look at the impedance curve for a chip ferrite bead below. It’s important to note that the impedance values will be different for differential-mode noise vs. Cutoff frequencies for these components can reach hundreds of MHz. This chip is the SMD version of a ferrite core you’ll find on a DC power cord.Ĭhip ferrites can also come packaged as low-profile chip components that provide common-mode or differential-mode noise filtering. The point of these components is to provide high inductance in a physically small package, much smaller than what you would see for a typical air-core inductor coil. These are also often called “chip ferrite beads”, so there is an important distinction with a standard ferrite core found on a power cord. These components are basically meant to be inductors with a ferrite core in a small SMD package with standardized land pattern. If you’re reading this on your laptop, there’s probably a ferrite core on the power cord. You’ll sometimes see this as a toroidal core wrapping around the output cord from your DC power plug. No matter the term used to refer to this component, it is intended to be placed on a power cord coming into the system with the idea of suppressing conducted common-mode noise coming from the grid. Be mindful of this when considering the use of toroidal ferrites for clamping power cords, and when looking at products on a manufacturer’s website. Some ferrite manufacturers will call this a ferrite choke or ferrite clamp rather than a ferrite core, and it gets confusing because some manufacturers will interchangeably use these terms for something else (either common-mode or differential-mode chokes, or chip ferrites). We often do a bad job of differentiating this from an inductor, board-mounted ferrite chip bead, and common-mode choke for reasons we’ll see momentarily. This is the most common reference to a ferrite bead you’ll find on forums, in guides, and elsewhere. To break through all the confusion, let’s look at each of these ferrite options to see which is the best option for your system. When used as inductors, the high μ value is what gives you a large inductance for a physically small package. These materials have a high μ value in the standard inductance equation. The point of using a ferrite is to take advantage of the high magnetic susceptibility of ferrimagnetic materials to suppress noise and radiation. Some EMI guidelines will also refer to the blanket “ferrite bead” when stating which component is your magic EMI solution, and typically without stating how or where to put the component. Then there are ferrite plates, which are not provided by every ferrite bead manufacturer. Some companies will use the correct name of a product when describing ferrites, while other product guides will just call everything a ferrite bead. Start looking at some component manufacturer websites, and you’ll find some mixed terminology around ferrite beads. Different Ferrites, Different Applications In particular, there are some problems an alternative ferrite can solve that can’t be approached with a ferrite bead. While they all obey the same laws of physics, they can provide different functions in your design depending on their form factor and placement. There are several types of ferrites to consider using in your design. But what about other types of ferrites? How does their electrical functionality compare to a simple ferrite bead? Very simply, ferrite beads, no matter their form factor, are intended to be a simple low-pass circuit. These components are usually put into a design with a simple intent: block everything except for DC current. Mention the word ferrite around some circuit designers, and the mind probably jumps to “ferrite bead”.
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