Characteristics and applications of commonly used soft magnetic cores

Magnetic powder core is a soft magnetic material made by mixing and pressing ferromagnetic particles with insulating media. Due to the small size of ferromagnetic particles (used at high frequencies ranging from 0.5 to 5 microns) and being separated by non magnetic electrical insulating film materials, on the one hand, they can isolate eddy currents, making the material suitable for higher frequencies; On the other hand, due to the gap effect between particles, the material has low permeability and constant magnetic permeability characteristics; Due to the small particle size, there is basically no skin phenomenon, and the variation of magnetic permeability with frequency is relatively stable. Mainly used for high-frequency inductors. The magnetic and electrical properties of magnetic powder cores mainly depend on the permeability of the powder material, the size and shape of the powder particles, their filling coefficient, the content of insulation medium, forming pressure, and heat treatment process.

The commonly used magnetic powder cores are iron core, permalloy core and iron silicon aluminum core.

The calculation formula for the effective permeability e and inductance of the magnetic core is: e=DL/4N2S 109

Among them: D is the average diameter of the magnetic core (cm), L is the inductance (sharing), N is the number of winding turns, and S is the effective cross-sectional area of the magnetic core (cm2).

(1) Iron powder core

The commonly used iron powder core is composed of carbon based iron magnetic powder and resin based carbon based iron magnetic powder. The price is the lowest among the powder cores. The saturation magnetic induction intensity value is around 1.4T; The magnetic permeability range is from 22 to 100; The initial magnetic permeability i exhibits good stability as a function of frequency; Good DC current superposition performance; But at high frequencies, the loss is high.

The variation of initial magnetic permeability of iron powder core with DC magnetic field strength

The variation of initial magnetic permeability of iron powder core with frequency

(2). Permalloy powder core

Permalloy powder cores mainly include molybdenum permalloy powder cores (MPP) and high flux powder cores.

MPP is composed of 81% Ni, 2% Mo, and Fe powders. The main characteristics are: the saturation magnetic induction intensity value is around 7500Gs; The magnetic permeability range is large, ranging from 14 to 550; Has the lowest loss in powder magnetic cores; Excellent temperature stability, widely used in space equipment, outdoor equipment, etc; The magnetostrictive coefficient is close to zero, and there is no noise generated when operating at different frequencies. Mainly used in high-quality factor Q filters below 300kHz, induction load coils, resonant circuits, commonly used in LC circuits with high temperature stability requirements, output inductors, power factor compensation circuits, etc., commonly used in AC circuits, with the most expensive powder core.

High magnetic flux powder core HF is composed of 50% Ni and 50% Fe powders. The main characteristics are: the saturation magnetic induction intensity value is around 15000Gs; The magnetic permeability range is from 14 to 160; Has the highest magnetic induction intensity and DC bias capability in powder magnetic cores; The magnetic core has a small volume. Mainly used in line filters, AC inductors, output inductors, power factor correction circuits, etc., commonly used in DC circuits, high DC bias, high DC, and low AC are more commonly used. The price is lower than MPP.