What is Ferrite Magnetic core
Ferrite Magnetic core are ceramic compounds of the transition metals with oxygen, which are ferrimagnetic but nonconductive. Ferrites that are used in transformer or electromagnetic cores contain iron oxides combined with 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:
Manganese-zinc ferrite (MnZn, with the formula MnaZn(1-a)Fe2O4). MnZn have higher permeability and saturation levels than NiZn.
Nickel-zinc ferrite (NiZn, with the formula NiaZn(1-a)Fe2O4). NiZn ferrites exhibit higher resistivity than MnZn, and are therefore more suitable for frequencies above 1 MHz.
For applications below 5 MHz, MnZn ferrites are used; above that, NiZn is the usual choice. The exception is with common mode inductors, where the threshold of choice is at 70 MHz.
As any given blend has a trade off of maximum usable frequency, versus a higher mu value, within each of these sub-groups manufacturers produce a wide range materials for different applications blended to give either a high initial (low frequency) inductance, or lower inductance and higher maximum frequency, or for interference suppression ferrites, a very wide frequency range, but often with a very high loss factor (low Q).
It is important to select the right material for the application, as the correct ferrite for a 100 kHz switching supply (high inductance, low loss, low frequency) is quite different to that for an RF transformer or ferrite rod antenna, (high frequency low loss, but lower inductance), and different again from a suppression ferrite (high loss, broadband)
Applications of Ferrite Magnetic core
There are two broad applications for ferrite cores which differ in size and frequency of operation: signal transformers, which are of small size and higher frequencies, and power transformers, which are of large size and lower frequencies. Cores can also be classified by shape, such as toroidal cores, shell cores or cylindrical cores.
The ferrite cores used for power transformers work in the low frequency range (1 to 200 kHz usually) and are fairly large in size, can be toroidal, shell, or shaped like the letters ‘C’, ‘D’, or ‘E’. They are useful in all kinds of electronic switching 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 lamination 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, such as in AM Radios and RFID tags.