I am usually glued to my notebook when working from home. It is often plugged into an electrical source, however, at times I need to be more mobile or seek a change of venue from my chair and desk. Often when reconnecting to the power source, I have to make adjustments to ensure that the little ball near the end of my power cable wire doesn’t get caught between the end of the sofa and a table that are close to the electrical receptacle that the power cable is plugged into.
Many times I’ve wondered what that little ball is for? On the surface it certainly didn’t appear to have any useful purpose other than as an annoyance that temporarily restricted me from extending the power cable’s electrical cord its full length. Recently, while web surfing. I stumbled upon a Brightside post, Ten things whose purpose we could never have guessed, that referred to my daily annoyance – the cylinder on my laptop’s power cable.
As it turned out, that cylinder has a name – ferrite bead. Is it possible that it has a useful purpose other than to annoy me? According to the folks at Brightside, the answer is yes! Ferrite beads suppress high-frequency noise in electronic circuits. The design is incredibly simple: it has an insert made from ferrite that the cable is wrapped around.
“Tell me more,” I say to myself. I googled ferrite beads for more info. According to my first source [Ref 1], a ferrite bead or ferrite choke is a simple hollow cylinder or bead that is made of ferrite material. It is used to suppress or filter the amount of high frequency electromagnetic interference (EMI) noise found in electronic circuits. Ferrite is a black semi-magnetic substance that is shaped like a cylinder and that consists of iron oxide along with a mixture of other metals. Ferrites are encased in rubber or plastic material to protect and keep the ferrite bead in place.
My second source [Ref 2] states that the simplest form of a ferrite bead is a conducting wire inserted through a hollow piece of ceramic material known as ferrite.
The electromagnetic properties of ferrite allow the material to influence the current flowing through the conductor. The way the material-current influence depends on the type of ferrite (e.g., manganese-zinc vs. nickel-zinc), and properties of the particular ferrite material being used. In many surface-mount ferrite beads, the conductor is formed into a coil structure, with individual windings layered between ferrite sheets. Therefore, the electrical characteristics depend also on the details of the winding construction.
Ferrite beads can be divided into two general categories: High-Q or resonant beads, and low-Q or non-resonant beads. High-Q beads are intended for applications that require high levels of resonance, such as oscillators and specialized filters. However, for power-supply filtering, the resonance needs to be minimized, therefore only low-Q beads are used for these applications.
Ferrite beads can be used for the removal of power line noises in cellular phones, PCs, TV tuners, audio players, DVDs, game machines, digital photo frames and several other electronic circuits.
So-o-o, the next time I get the ferrite ball of my computer’s power supply caught between the table and the end of the sofa, I’ll remember that it is performing a necessary function.
- Filters: Ferrite Beads, Future Electronics, http://www.futureelectronics.com/en/filters/ferrite-beads.aspx
- Clean Power for Every IC, Part 3: Understanding Ferrite Beads, by Robert Keim for All About Circuits, September 30, 2015, http://www.allaboutcircuits.com/technical-articles/clean-power-for-every-ic-part-3-understanding-ferrite-beads/