Core Types Used by Butler Winding: Ferrites (ceramic structures)
Modern electronic designs demand magnetic devices to operate at ever increasing high frequencies. Higher frequencies permit smaller magnetic devices up to a point; that point being excessive heat loss and its associated temperature rise. Of course sufficiently high temperatures will cause imminent failures. Even mildly excessive temperatures will shorten insulation life and eventually cause the magnetic device to fail prematurely. This can cause a real problem for product manufacturer’s and especially for their customers if the manufacturer’s products fail within a year or two after delivery. Winding losses are one source of heat. The other source is core loss. Core loss is caused by magnetic hysterisis. The hysterisis produces eddy currents. Eddy currents flow through the resistance of the core material and produce heat. Core materials with high electrical resistivity can be operated at higher frequencies and/or higher flux density levels. Consequently designers sought to discover or develop core materials with high resistivity. Ferrite core materials were a resulting viable solution. Ferrites exhibit high permeability and high resistivity. Ferrites are also reasonably stable (repeatable properties) over time and temperature. Three basic categories of ferrites are discussed below. The manganese zinc and manganese nicker categories can be divided into various grades of ferrites.