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In order to obtain Z good suppression effect of common mode interference, the common mode inductor core must have high permeability and excellent frequency characteristics. In the past, ferrite was used as the core material of common mode inductor, which has excellent frequency characteristics and low cost. However, ferrite also has some insurmountable weaknesses, such as poor temperature characteristics and low saturation magnetic induction, which are limited in application.
In recent years, the emergence of Fe-based Nanocrystalline Ribbons has added an excellent core material for common mode inductance. The manufacturing process of Soft Magnetic Materials Fe-based Nanocrystalline Ribbons is as follows: firstly, amorphous alloy strips with a thickness of about 20-30 microns are made by rapid solidification technology, wound into iron core, and then further processed to form nanocrystals. Compared with ferrite, nanocrystalline alloys have some unique advantages:
High saturation magnetic induction:
The BS of Fe based nanocrystalline alloy is up to 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 decrease sharply. In practical application, there are many occasions with high interference intensity (such as high-power variable frequency motor). If ordinary ferrite is used as common mode inductance, the iron core is likely to be saturated, which can not ensure the noise suppression effect under high-intensity interference. Due to the high saturation magnetic induction strength of nanocrystalline alloy, its anti saturation characteristics are undoubtedly better than ferrite, which makes nanocrystalline alloy very suitable for the occasion of resisting high current and strong interference.
High initial permeability:
The initial permeability of nanocrystalline alloy can reach 100000, 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 has an excellent inhibitory effect on weak interference. This is especially suitable for anti weak interference common mode filters requiring very small leakage current. In some special occasions (such as medical equipment), the equipment causes leakage current through ground capacitance (such as human body), which is easy to form common mode interference, and the equipment itself is very strict. At this time, using nanocrystalline alloy with high permeability to make common mode inductor may be z a good choice. In addition, the high permeability of nanocrystalline alloy can reduce the number of coil turns and reduce the distribution parameters such as parasitic capacitance, so as to increase the formant frequency in the insertion loss spectrum caused by the distribution parameters. At the same time, the high permeability of nanocrystalline iron core makes the common mode inductance have higher inductance and impedance, or reduce the volume of iron core on the premise of the same inductance.
Excellent temperature stability:
The Curie temperature of Fe based nanocrystalline alloy is above 570oc. In the case of large temperature fluctuation, the change rate of properties of nanocrystalline alloy is significantly lower than that of ferrite, has excellent stability, and the change of properties is close to linear. Generally, the change rate of main magnetic properties of nanocrystalline alloys is less than 10% in the temperature range of - 50oc - 130oc. In contrast, the Curie temperature of ferrite is generally below 250oC, and the change rate of magnetic properties sometimes reaches more than 100%, which is nonlinear and difficult to compensate. The temperature stability of nanocrystalline alloy combined with its unique low loss characteristics provides loose temperature conditions for device designers. Fig. 3 shows the temperature characteristics of saturated magnetic induction of different materials.
Flexible frequency characteristics:
Through different manufacturing processes, nanocrystalline iron core can obtain different frequency characteristics. 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 ferrite. It should be pointed out that any filter can not expect to achieve noise suppression in the whole frequency range with one core material, but should select different core materials, sizes and turns according to the filter frequency band required by the filter. Compared with ferrite, nanocrystalline alloys can obtain the required frequency characteristics more flexibly by adjusting the process.
Since the development of Fe 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 permeability, high saturation magnetic induction and flexible and adjustable frequency characteristics, nanocrystalline alloys have attracted more and more attention in the field of anti common mode interference filters. There are iron-based nanocrystalline alloy common mode inductor cores that can be supplied in large quantities 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 more and more broad application prospects in China.
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