Toroids have the best possible shape from the magnetic point of view. The flux path is completely closed so the capabilities of the ferrite are fully exploited. Especially for high permeability ferrites
the effect of even a minor airgap in the magnetic circuit
can spoil up to 50% of the effective permeability. A further
advantage is the very low leakage fi eld which makes it a
suitable shape for power and pulse transformers.
Ring cores are mainly used for pulse- and wide band transformers and interference suppression coils but also in
special power supplies.