What is a iron silicon aluminum Magnetic core (ferrosilicon core)?
A ferrosilicon core is one of several magnetic components commonly referred to as a magnetic powder core. Magnetic powder cores originated in the early days of electronic components. In the 1920s, iron powder cores were used in early radios. In the 1930s, a ferrosilicon aluminum alloy and a molybdenum permalloy alloy (80% nickel-iron) were developed. In the 1970s, a high flux core (50% nickel-iron) was developed. A powder core is made by grinding an existing metal alloy into fine particles, and then an insulating material is applied to the surface of the particles (this can control the size of the air gap). These powders are pressed into different core powder shapes under high pressure. The ferrosilicon powder core material is approximately 85% iron, 6% aluminum, and 9% silicon. The special method of processing the powder, together with the use of special coating materials, can produce a core with a lower core loss than the original ferrosilicon powder and much lower than the iron core.
Which applications are best suited for use with ferrosilicon cores?
The ferrosilicon core is ideal for energy storage filter inductors in switching power supplies. A 10,500 Gaussian-rich ferrosilicon core provides a higher energy storage capacity than a gap-sized ferrite or iron powder core of the same size and permeability.
Compared with iron powder cores, iron-silicon-aluminum performs better at high temperatures. In some applications, the use of iron-silicon-aluminum is also smaller than that of iron powder cores.
In silicon-aluminum cores, which are required to pass large AC voltages without generating a saturated noise filter inductor. The use of a ferrosilicon core reduces the size of the in-line filter because fewer turns are required than with ferrite. The ferrosilicon also has a magnetostriction coefficient close to zero, that is, it is very quiet in the audible frequency range of noise or in-line current roughening.
The high magnetic flux density and low core loss make the ferrosilicon core suitable for power factor correction circuits as well as unidirectional drive applications such as flyback transformers and pulse transformers.
A small addition of silicon to iron (around 3%) results in a dramatic increase of the resistivity of the metal, up to four times higher. The higher resistivity reduces the eddy currents, so silicon steel is used in transformer cores. Further increase in silicon concentration impairs the steel’s mechanical properties, causing difficulties for rolling due to brittleness.
Among the two types of silicon steel, grain-oriented (GO) and grain non-oriented (GNO), GO is most desirable for magnetic cores. It is anisotropic, offering better magnetic properties than GNO in one direction. As the magnetic field in inductor and transformer cores is always along the same direction, it is an advantage to use grain oriented steel in the preferred orientation. Rotating machines, where the direction of the magnetic field can change, gain no benefit from grain-oriented steel.