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Iron Powder Cores
Iron powder cores are made from finely defined particles of iron.
The particles are insulated from each other but bound together with
binding compound. The mixture is pressed to the finished shape under
heavy pressure and a system of distributed air gap is thereby created.
The finished iron powder core has a maximum permeability of about
110, which is lower than the raw material used, iron.
Iron
powder cores may come in numerous sizes and configurations, each
of which is available in different materials. However, the toroidal
cores are the most efficient configuration due to its highly shelf-shielding
characteristic. It is seldom necessary to shield a toroidal inductor
as most of the flux lines are contained within the core.
Iron
powder cores can be divided into two basic categories according
to its permeabilities, namely the RF material range and the power
material range.
The
RF material cores, with permeabilities range from 3 to 35, are especially
noted for their high core temperature stability, good flux characteristics
and low loss. They are ideally suited for RF transformers and broadband
inductors. The RF material cores are in high demand for applications
in the communications industry. Some radar applications use iron
powder cores at frequencies well above 1 GHz.
The
power material cores have higher permeabilities ranging from 50
to 110. Unlike ferrite cores, the high permeability iron powder
cores are capable of handling higher flux densities and higher power
levels without saturating. Typical applications for cores with permeabilities
above 60 include the EMI filters, DC chokes, and line filters. For
cores with permeabilities in the 40 to 60 ranges, they are widely
used as RF transformers, pure inductors, and filters for switch
mode power supplies.
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