Toroidal inductors are passive electronic components, typically consisting of a circular ring-shaped magnetic core of high magnetic permeability material such as iron powder or ferrite, around which wire is coiled to make an inductor. Toroidal coils are used in a broad range of applications in AC electronic circuits, such as high-frequency coils and transformers.
They could be Round, Square & Flat Shapes
They could be Round, Square & Flat Shapes
An inductor with a closed-loop core can have a higher magnetic field and thus higher inductance and Q factor than similarly constructed coils with a straight core (solenoid coils). This is because the entire path of the magnetic field lines is within the high permeability core, while in an inductor with a straight core the magnetic field lines emerging from one end of the core have a long air path to enter the other end. In recent years, the use of toroidal (donut) shape cores has increased greatly. The advantage of the toroidal shape is that due to its symmetry the amount of magnetic flux that escapes outside the core (leakage flux) is minimum, therefore it radiates less electromagnetic interference (EMI) to nearby circuits or equipment. EMI is of increasing importance in modern low power, high frequency electronics.
A side effect in torus-shaped inductors is that, because the winding surrounds the central hole and the current traverses the winding in a circular direction, there is a weak poloidal magnetic flux that threads the "donut hole" in the center of the torus, in addition to the main toroidal flux direction parallel to the core of the torus.
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Ferrite toroids offer high magnetic efficiency as there is no air gap and the cross-sectional area is uniform. Magnetic toroids are available in many sizes (outside diameters ranging from 2 mm to 140 mm) and materials (permeabilities ranging from 900µ to 10,000µ). Different coatings can be applied to ferrite toroids to increase winding ease and improve voltage breakdown. Hardware, such as toroid mounts and headers, is available.
Typical applications for high permeability ferrite toroids, 5,000µ J material and 10,000µ W material, include common mode chokes, EMI filters, broadband transformers, pulse transformers and current transformers. Special sizes of ferrite toroids are available in 5,000 J material for Ground Fault Interrupter (GFCI) applications. 900µ L material, 2,300µ R material, 2,500µ P material, and 3,000µ F material toroids are excellent choices for high frequency transformers.
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