Commonly Used Soft Magnetic Core Iron Powder Core Permalloy Powder Core Iron-Silicon-Aluminium Powder Core
Magnetic powder core is a kind of soft magnetic material made by mixing and pressing ferromagnetic powder and insulating medium. Ferromagnetic particles are very small (0.5-5 micron used at high frequencies) and are separated by non-magnetic insulating film materials. Therefore, on the one hand, they can isolate eddy currents and materials are suitable for higher frequencies; on the other hand, because of the gap effect between particles, the materials have low permeability and constant permeability; on the other hand, because of the small size of particles, skin-gathering phenomenon does not occur. The change of rate with frequency is more stable. Mainly used for high frequency inductance. The magnetoelectric properties of magnetic powder cores mainly depend on the permeability of powder materials, the size and shape of powder particles, their filling coefficient, the content of insulating medium, forming pressure and heat treatment process.
The commonly used magnetic powder cores are iron powder cores, permalloy powder cores and iron-silicon-aluminium powder cores. The formula for calculating the effective permeability and inductance of the core is: Mu e = DL/4N2S*109. Among them: D is the average diameter of the core (cm), L is the inductance (enjoyment), N is the number of winding turns, S is the effective cross-section area of the core (cm2).
(1) Iron Powder Core
The common iron powder core is composed of carbon-based ferromagnetic powder and resin-based ferromagnetic powder. The price is the lowest among the powder cores. The saturated magnetic induction intensity is about 1.4T, the permeability range is 22-100, the initial permeability is stable with frequency, the DC current superposition performance is good, but the loss is high at high frequency. The initial permeability of iron powder core varies with the intensity of DC magnetic field. Variation of Initial Permeability of Iron Powder Core with Frequency.
(2) Permalloy Powder Core
The main powders of permalloy are molybdenum permalloy powders (MPP) and high flux powders (High Flux).
MPP is composed of 81% Ni, 2% Mo and Fe powder. The main characteristics are: the saturated magnetic induction intensity is about 7 500 Gs; the permeability range is large, ranging from 14 to 550; the lowest loss is found in the powder core; the temperature stability is excellent, and it is widely used in space equipment and open-air equipment; the magnetostriction coefficient is close to zero, and there is no noise when working at different frequencies. It is mainly used in high quality factor Q filter, induction load coil, resonant circuit, LC circuit which requires high temperature stability, output inductance, power factor compensation circuit, etc. It is commonly used in AC circuit, and the price of powder core is the most expensive.
High flux core HF is composed of 50% Ni and 50% Fe powder. The main characteristics are: the saturated magnetic induction strength is about 15 000 Gs; the permeability range is from 14 to 160; the powder core has the highest magnetic induction strength, the highest DC bias capacity; and the core is small in size. Mainly used in line filters, AC inductance, output inductance, power factor correction circuit, etc., in DC circuit is commonly used, high DC bias, high DC and low AC are much more used. The price is lower than MPP.
(3) Ferrosilicate Aluminum Powder Cores
The core of Fe-Si-Al powder is composed of 9% Al, 5% Si and 85% Fe powder. Mainly replace iron powder core, loss is 80% lower than iron powder core, can be used at frequency above 8 kHz; saturated magnetic induction is about 1.05T; permeability is from 26 to 125; magnetostriction coefficient is close to 0, no noise is generated when working at different frequencies; DC bias capacity is higher than MPP; has the best performance-price ratio. Mainly used in AC inductor, output inductor, line filter, power factor correction circuit, etc. Sometimes it can be used as transformer core instead of air gap ferrite.
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