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Magnetic Materials Application

Because to do 6KW, 0.9MHz high-frequency welding machine must contact the magnetic, the current high-frequency welding machine has been initially completed, so the basic concept of magnetic summing up, one for their own review in the future, two for switching power supply Friends provide references and clarify ideas.
Magnetics is not commonly used because it is not commonly used, so it is relatively unfamiliar, and it is often confined to the switching power supply industry. Most of the switching power supplies are designed with reference to other circuits, and they are rarely designed by themselves, so they are often There is no deep understanding of theory. This is one. There are two units of magnetics, such as MKS (m-kilogram-seconds) and CGS (centimeter-gram-seconds). The domestic teaching generally adopts the MKS system, but the project actually adopts the CGS value, and there are too many terms. Confuse this for two. There are many kinds of magnetic materials, and the parameter measurement is inconvenient. There are also few instrument measurements, such as magnetic permeability, induced magnetic induction, etc. The most easy inductance value, no general multimeter, all need special instruments, this is its three . These above have restricted the popularization and promotion of magnetism.
According to actual engineering needs, we generally need to understand such a few indicators
1, the inductance value, this proposal uses a professional instrument to measure directly, the price of the handheld is not expensive
2, heat loss, this proposal uses a temperature gun to measure, the price is not expensive, as long as the guarantee can be within the scope of work.
3, saturation magnetic induction, is not allowed to magnetic saturation, otherwise this inductor failure led to equipment explosion, especially switching power supply, the core of this article is to obtain this value.

This article is based on the CGS system of practical units, using Gs (Gaussian) and Oe (Oster) units. The objects of discussion are uniform closed magnetic materials such as magnetic rings and E-type transformers. Pi is pi
1. The generation of a magnetic field is based on a closed current in practice. When a magnetic ring has an external closed coil, the magnetic motive force generated by this coil is expressed in mmf (equivalent to the voltage concept of the electric field):
Mmf = 0.4π*NI, N refers to the number of turns, I is the current through the coil, this is the prime mover to generate the magnetic field
2. Because the magnetic field generated by the internal micro current is synchronized to the outside, when the external magnetic field is removed, the internal magnetic field also forms a closed large magnetic field in the same direction, and it takes a long enough time to be disturbed by the molecular thermal motion.
One depends on different materials, which can be divided into soft magnetic material and hard magnetic material. When the external current is cancelled, the internal magnetic field remains for a long time, forming a magnet. Soft magnetic materials generally have an internal magnetic field that disappears immediately after the external magnetic field is removed, but this also requires a time, because the existence of this time, or the synchronization of the internal micro-magnetic field with the external magnetic field requires time, this generates a hysteresis loop, that is, Loss, the higher the general frequency, the greater the loss.
3, the size of the specific magnetic field that is the magnetic field strength, subject to the loop length of the magnetic material:
H = mmf / L (Oster) When it is a magnetic ring, L = 2πR, R is the radius of the magnetic ring, note that L unit is cm (cm)
4, H is the motive force of the magnetic field, when encountering different materials, their internal miniature self-closing current loop will be consistent with the direction of the external magnetic field, enhancing its internal magnetic field, so with magnetic induction B and permeability μ
B = μ*H (Gs Gaussian)
1T (Tesla) = 10000Gs (Gaussian)
5, μ = 1 in vacuum, other materials are generally greater than 1
6, comprehensive above:
B = 0.2μ*N*I/R
As long as the calculated value does not exceed the saturation magnetic induction value of the material
7, μ and Bmax, generally magnetic material manufacturers can provide, and according to the classification of materials, we can also roughly know the scope:
Silicon steel Manganese zinc Nickel zinc Iron powder core Iron silicon aluminum
Applications Power Frequency <1MHz >1MHz High Frequency Filtering High Frequency Filtering
μ 1.5K 750~15K 15~1500 4~100 26~125
Bmax(T)1.5~1.8 0.3~0.5 0.3~0.5 0.5~1.4 1
8, material description
a, silicon steel sheet is generally used for power frequency transformer and motor equipment, working frequency is near 50Hz
b, manganese and zinc because of cost-effective, a large number of current applications in the power level of switching power supply, according to different frequency of wear, can be divided into many levels, generally speaking, μ higher the greater the loss, so the higher the u value of the frequency The lower.
c. Nickel and zinc are complementary to manganese and zinc. They are generally used at higher frequencies because they are larger than 1 MHz and are widely used in EMI devices to resist radiation interference. Nickel-zinc magnetic rings are essentially non-conductive, and this is the simplest place to distinguish manganese zinc (manganese zinc magnetic ring conductive).
d, iron powder core because of cost-effective, a large number of applications in the switching power supply output filter, this often with a strong DC component and AC component is not, the use of low iron powder core permeability can be anti-magnetic saturation.
e, iron silicon aluminum prices are higher, but the performance is 2 times that of iron powder core, the function is the same as the iron powder core, and often replaces the iron powder core in order to reduce the heat.

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