More expensive magnetic materials are also available, based on metallic lamination, even amorphous, or nano-crystalline materials. Those laminated materials have much higher values of saturation flux density, that allows to reduce dimensions especially for applications switching at low frequency values, and a much more stable behaviour with temperature, so they are preferred in case of critical environment conditions.
From the construction’s point of view, there are many different ways to arrange windings, but we can consider basically two main kinds of winding layout with complementary characteristics, the multifilar style and the separated sectors style. The aim of the multifilar winding process is to achieve low leakage inductance values, in order to get very short rise times but, on the other hand, the coupling capacity gets very high values; it is used mainly for low working voltage applications as the isolation is guaranteed entirely by the isolating covering material of the wires. You can get very similar characteristics, even by placing the windings one above the other and not all together in parallel. The separated sectors winding style is preferable for high working voltage applications, as the isolation is guaranteed not only by the wires but also by other insulating materials between the windings. This style is characterized by low coupling capacity and high leakage inductance. They are tipically used in IGBTs, power MOSFETs and BJTs high frequency firing or in lower frequency applications with Thyristors and Triacs. Standard versions are available with one or two secondary windings.
Toroidal components generally have very good technical features but the production process is by nature a one-by-one building style, that cannot be made automatically. This is the reason why the final cost is much higher if compared with the components based on linear winding process.