The most obvious difference between toroidal coils and other coils is the shape. Toroidal coils are a donut or ring shape. This is due to the different shape of the core material. A donut shaped core is used and the wire is repeatedly taken through the central hole and wrapped back around the outside.
Other coils tend to be cube or rectangular shaped, with the wire wrapped around a bobbin that then has a set of cores fitted through the centre and around the outside of the bobbin. Due to the different shape of the coil, a specialised manufacturing process is required.
Toroidal coils do not have standard mounting, like other coils. Their connections tend to be by flying leads, although smaller coils can be mounted on bases that allow easy insertion into PCBs.
The main advantage of toroidal coils is that the shape of the core minimises the escape of magnetic flux. The core is a closed loop. The core does not have ends or corners from where the flux can escape. These reduced losses lead to greater efficiency and less electromagnetic interference (EMI).
The windings can be distributed around the whole of the core, which gives better utilisation of the core material, better coupling between separate windings and further helps the efficiency. The closed loop also gives a higher magnetic field, which leads to higher inductance and Q factor.
This improved efficiency usually means that more power can be obtained pro rata to size from a toroidal transformer. This is utilised in mains power transformer applications.
Traditionally, the audio industry saw great benefit in the use of toroidal coils due to the reduced distortion and fringing effects, which they believed produced a cleaner sound. However, here at AGW, we believe that normal coils can match the quality of toroidal transformers, and this is supported by the work we have undertaken with loudspeaker manufacturer; Russel K.
Two common types of toroidal chokes are Common Mode Chokes and Differential Mode Chokes.
Both are used for the blocking (or “choking”) of unwanted frequencies or interference.
The Common Mode Choke utilises the toroidal shape by putting two windings on one core. The windings can be used to cancel out interference, because they are wound in different directions. They provide suppression without saturating.
AGW has the design and manufacturing facilities for the production of toroidal coils. Please see –