Inductor Construction - UC Santa Barbara（感应式建筑加州大学圣芭芭拉分校）.pdf

Inductor Construction Toroidal Cores. There are many different types of magnetic material used for fabricating inductors. The purpose of the material is to provide permittivity greater than µ so that the inductors can be O made more compactly and with fewer turns of wire. This can reduce skin effect losses in the wire and reduce coupling to other inductive components in the circuit, but the circuit losses then may be limited by the magnetic material itself. There are charts of typical unloaded Q’s that can be obtained from various materials. There are correct and incorrect ways of winding the wire around the core. Each pass 1 through the center of the core counts as one turn. See Fig. 1-28 from Bowick (attached) for details on winding. The idea is to minimize capacitive coupling between the turns while still getting enough turns on the core to obtain the needed inductance. 2 The toroids are designated by a code : T-xxx-yy or FT-xxx-yy. T stands for iron powder materials and FT for ferrite. The first 3 digits (xxx) indicates the core outer diameter in units of 0.01” (10 mils). The last number (yy) designates the code for material type. The iron cores are color coded. The ferrite materials have much higher permeability and so require fewer turns to obtain a given inductance. They are also essential to use for wideband applications like untuned transformers. The iron powder cores simply do not work for this purpose. For narrowband, tuned applications, either type can be used in the frequency ranges in which they provide high unloaded Q. This would include matching networks such as the L or Pi network. Note that the powdered iron generally has lower losses than the ferri