Toroidal inductors and transformers

Toroidal inductors and transformers are inductors and transformers which use magnetic cores with a toroidal (ring or donut) shape. They are passive electronic components, consisting of a circular ring or donut shaped magnetic core of ferromagnetic material such as laminated iron, iron powder, or ferrite, around which wire is wound.

Although in the past closed-core inductors and transformers often used cores with a square shape, because of their superior electrical performance the use of toroidal-shaped 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 low, therefore it is more efficient and thus radiates less electromagnetic interference (EMI).

Toroidal inductors and transformers are used in a wide range of electronic circuits: power supplies, inverters, and amplifiers, which in turn are used in the vast majority of electrical equipment: TVs, radios, computers, and audio systems.

In general, a toroidal inductor/transformer is more compact and lighter than other shaped cores. This is especially the case for power devices.

Because the toroid is a closed-loop core it will have a higher magnetic field and thus higher inductance and Q factor than an inductor of the same value with a straight core (solenoid coils). This is because most of the magnetic field is contained within the core. By comparison, with an inductor with a straight core, the magnetic field emerging from one end of the core have a long path through air to enter the other end.

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