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In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents). Because of their comparatively low losses at high frequencies, they are extensively used in the cores of RF transformers and inductors in applications such as switched-mode power supplies, and ferrite loopstick antennas for AM radio receivers.
Ferrites are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but nonconductive. Ferrites that are used in transformer or electromagnetic cores contain nickel, zinc, and/or manganese compounds. They have a low coercivity and are called "soft ferrites" to distinguish them from "hard ferrites", which have a high coercivity and are used to make ferrite magnets. The low coercivity means the material's magnetization can easily reverse direction without dissipating much energy (hysteresis losses), while the material's high resistivity prevents eddy currents in the core, another source of energy loss. The most common soft ferrites are:
There are two broad applications for ferrite cores which differ in size and frequency of operation: signal transformers are of small size and higher frequencies, power transformers are of large size and lower frequencies. Cores can also be classified by shape: there are toroidal cores, shell cores, cylindrical cores, and so on.
The ferrite cores used for power transformers are working in the range of low frequencies (1 to 200 kHz usually) and are quite big in size, can be toroidal, or shell or C shape and are useful in all kinds of switching electronic devices (especially power supplies from 1 watt to 1000 watts maximum, since more powerful applications are usually out of range of ferritic single core and require grain oriented laminations cores).
The ferrite cores used for signals have a range of applications from 1 kHz to many MHz, perhaps as much as 300 MHz, and have found their main application in electronics.