When researching inductor filtering, I often struggle with the selection of inductors. I have been out of school for a long time, and I have lost all the previous knowledge about inductors, so that I can't understand why the inductor is saturated, and it is precisely what I think that causes the saturation of the inductor. For the DC current to be retained, the concepts of inductance and capacitance are completely equivalent, and it is wrong to think that the DC current has no effect on the inductance.
First of all, the saturation current is not equal to the maximum current. For DC current, it can be considered that the impedance of the inductor is 0, and an inductor with a saturation current of 1A is selected. It does not mean that the maximum current is 1A, and it can be larger, as long as the inductance wire diameter supports it. Excessive current means that the inductance is too saturated, and the inductance is not an inductance, but a metal conductor, because the saturated inductance will not affect the AC current.
For inductance, the most familiar is electromagnetic induction, magnetism generates electricity and electricity generates magnetism, and a changing magnetic field generates an electric field, but it is not a changing electric field that generates a magnetic field. Although an electric field generates a magnetic field, a constant electric field generates a constant magnetic field. A changing magnetic field, a changing magnetic field produces an electric field, is such a relationship.
The microscopic principle of generating a magnetic field: the electrons revolve around the outer orbit of the atom, and the electrons will generate a weak magnetic field during the rotation of each layer. The magnetic field of each layer is different, so the directions are also different, but the role of the Zero force, no magnetism. When a coil is energized, a magnetic field will also be generated. After the magnetic field lines pass through the magnetic material, the electrons start to rotate, and the magnetic field lines generated by the coil are eliminated. Magnetic saturation occurs when the electrons in the material all rotate in the same direction.
After the magnetic saturation occurs, if the AC current (the part that needs to be filtered out) passes through, the positive current (greater than 0) will undoubtedly deepen the degree of saturation without damping, and the negative current (less than 0), according to the degree of magnetic saturation, there are There may be some damping, in short, it will affect the filtering effect, not to mention the AC current component of 0, which will not have any filtering effect. This is a bit like the question of whether the op amp current works in the amplification region or the saturation region. Therefore, it is difficult for the AC current to cause saturation of the inductor, at least not all the time. The DC current will instead keep the inductor in a saturated state.
Magnetic saturation can be considered as the limit of the inductance to respond to the magnetic field. The magnetic field continues to increase, and the inductance will not respond to changes in the magnetic field. Magnetic flux = L * I / N , so the larger the inductance, the smaller the saturation current. The inductance is related to the physical characteristics of the inductance L=μ×S*N^2/l, L represents the inductance, μ represents the magnetic permeability of the magnetic core, S represents the cross-sectional area of the magnetic core, N represents the number of turns of the coil, and l represents the magnetic core It is estimated that the increase in the saturation magnetic flux is not proportional to L*I, resulting in an inverse proportional relationship between the saturation current and the inductance. From the above inductance formula, we can also see why the air-core inductance is difficult to saturate and the iron-core inductance is easy to saturate.