Advantages of iron-based nanocrystalline alloys

In order to obtain the best suppression effect on common mode interference, the common mode inductor core must have high magnetic permeability, excellent frequency characteristics, etc. In the past, ferrite was mostly used as the core material of common mode inductors, which has the advantages of better frequency characteristics and low cost. However, ferrite also has some insurmountable weaknesses, such as poor temperature characteristics, low saturation magnetic induction, etc., which are limited in application. In recent years, the emergence of iron-based nanocrystalline alloys has added an excellent core material for common-mode inductors. The manufacturing process of iron-based nanocrystalline alloy is as follows: firstly, a thin strip of amorphous alloy with a thickness of about 20-30 microns is made by rapid solidification technology, and then wound into an iron core and then further processed to form nanocrystals. Compared with ferrite, nanocrystalline alloy has some unique advantages: High saturation magnetic induction: Bs of iron-based nanocrystalline alloy reaches 1.2T, which is more than twice that of ferrite. As a common mode inductor core, an important principle is that the core cannot be magnetized to saturation, otherwise the inductance will drop sharply. However, in practical applications, there are many occasions where the interference intensity is relatively large (such as high-power variable frequency motors). If ordinary ferrite is used as a common-mode inductor, the iron core may be saturated, and the performance under high-intensity interference cannot be guaranteed. Noise suppression effect. Due to the high saturation magnetic induction of nanocrystalline alloys, its anti-saturation characteristics are undoubtedly better than those of ferrite, making nanocrystalline alloys very suitable for occasions that resist high current and strong interference. High initial magnetic permeability: The initial magnetic permeability of nanocrystalline alloy can reach 100,000, which is much higher than that of ferrite. Therefore, the common mode inductor made of nanocrystalline alloy has large impedance and insertion loss under low magnetic field, and is suitable for weak interference Has an excellent inhibitory effect. This is especially suitable for weak interference common mode filters that require extremely small leakage currents. In some specific occasions (such as medical equipment), the leakage current caused by the equipment through the ground capacitance (such as the human body) is easy to form common mode interference, and the equipment itself has extremely strict requirements on this. At this time, it may be the best choice to use a nanocrystalline alloy with high magnetic permeability to make a common-mode inductor. In addition, the high magnetic permeability of the nanocrystalline alloy can reduce the number of turns of the coil and reduce the distribution parameters such as parasitic capacitance, thus increasing the resonant peak frequency on the insertion loss spectrum caused by the distribution parameters. At the same time, the high magnetic permeability of the nanocrystalline iron core enables the common mode inductor to have higher inductance and impedance values, or reduce the volume of the iron core under the premise of the same inductance. Excellent temperature stability: The Curie temperature of iron-based nanocrystalline alloy is as high as 570oC or more. In the case of large temperature fluctuations, the performance change rate of nanocrystalline alloy is obviously lower than that of ferrite, which has excellent stability, and the change of performance is close to linear. Generally, in the temperature range of -50oC--130oC, the change rate of the main magnetic properties of nanocrystalline alloys is within 10%. In contrast, the Curie temperature of ferrite is generally below 250oC, and the change rate of magnetic properties sometimes reaches more than 100%, and it is nonlinear and difficult to compensate. This temperature stability of nanocrystalline alloys, combined with their unique low loss characteristics, provides device designers with relaxed temperature conditions. Figure 3 shows the temperature characteristics of the saturation magnetic induction of different materials. Flexible frequency characteristics: Through different manufacturing processes, nanocrystalline iron cores can obtain different frequency characteristics, and with appropriate coil turns, different impedance characteristics can be obtained to meet the filtering requirements of different bands, and its impedance value is much higher than that of iron cores. Oxygen. It should be pointed out that any filter cannot expect to use one core material to achieve noise suppression in the entire frequency range, but should choose different core materials, sizes and turns according to the filtering frequency band required by the filter. Compared with ferrite, nanocrystalline alloys can more flexibly adjust the process to obtain the required frequency characteristics. Since the development of iron-based nanocrystalline alloys in the late 1980s, they have been widely used in switching power supply transformers, transformers and other fields. Due to the advantages of high magnetic permeability, high saturation magnetic induction, and flexible and adjustable frequency characteristics of nanocrystalline alloys, they are also receiving more and more attention in the fields of anti-common-mode interference filters. Iron-based nanocrystalline alloy common-mode inductor cores that can be supplied in large quantities already exist abroad. With the gradual deepening of people's understanding of nanocrystalline alloys, it can be expected that the common mode inductors manufactured by them will have a wider application prospect in China.

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