The main difference is that the cross-section of the O-type iron core is "round", while the cross-section of the ring-type iron core is "square".
Ring-type transformer: the use of high-quality cold-rolled silicon steel sheet (sheet thickness is generally 0.35mm or less), seamlessly rolled into, which makes its core performance is better than the traditional stacked-sheet core. Toroidal transformer high efficiency, because of its core without air gap, stacking coefficient can be as high as 95% or more, core permeability can be taken 1.5-1.8T (stacked chip core can only be taken 1.2-1.4T), the electrical efficiency of up to 95% or more, and no-load current is only stacked type 10%. Its windings are evenly wound on the toroidal core, and this structure results in small magnetic leakage and electromagnetic radiation, which can be used on high-sensitivity electronic devices, low-level amplifiers and medical equipment.
O-type transformer: the use of the core structure is stacked, can effectively reduce the eddy current, the same can reduce the temperature rise of the transformer, because the eddy current is actually another form of energy loss, this is similar to the square transformer. Because of its advantage of no folded corners, will make the distribution of the magnetic field more uniform.