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Introduction to Magnetic Characteristics


General Information: The magnetic characteristics shown result from testing toroidal cores. The magnetization curves shown have a typical tolerance of +20%, -10%. Other configurations such as E Cores and U Cores will produce slightly different results due to the effects of leakage associated with the geometry.

These characteristics were measured at room temperature. The temperature coefficient of initial permeability for each material is listed in General Material Properties. The temperature coefficient of percent permeability versus both DC magnetizing force and peak AC flux density ranges from -100 to -400 ppm/C°. The combination of these coefficients will generally result in an increase in inductance with increasing temperature even under biased conditions.

The percent change in permeability is directly proportional to the percent change in AL value. The cores are manufactured to the AL value rather than to the referenced permeability.

Since iron powder cores are normally used in inductor applications the magnetization curves shown are in relation to permeability.

DC Magnetization: The curves illustrate the effect of DC Magnetizing force on percent initial permeability for the materials shown. As the level of DC magnetizing force increases, the materials gradually experience a reduction in permeability. This “soft” saturation characteristic results from the distributed air-gap in the iron powder core materials.

The formula in the body of the graph is used to calculate the DC Magnetizing Force in oersteds. The mean magnetic path (l) for each core is included in the part number listing.

These curves are based on a peak AC flux density of 10 gauss (1 mT). The response to DC magnetizing force is affected by the level of peak AC flux density present.

AC Magnetization: The curves illustrate the effect of Peak AC Flux Density on percent initial permeability. As the level of peak AC flux density increases, the materials experience an increase in permeability up to an AC flux density of between 3000 and 6000 gauss. Beyond this level, the material begins to saturate. These curves are the result of tests performed from 60 Hz to 10 kHz.

The formula in the body of the graph is used to calculate the peak AC flux density in gauss. The Cross-Sectional Area (A) for each core is included in the part number listing.

The AL values listed are based on a peak AC flux density of 10 gauss (1 mT). Testing cores at a higher flux density can have a significant effect on measured results.

The curves, Effective Permeability vs Frequency, - show how the permeability of each material is affected by frequency.

A typical coil wound with multiple turns will have a measurable amount of interwinding capacitance which acts in parallel with the coil. This interwinding capacitance will cause the coil to become self-resonant. In order to avoid this effect, the data at the highest frequencies was taken with a single turn.


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