Some notes on soft magnetic ferrite core


Ferrite core is made of non-metallic magnetic material with compact uniform ceramic structure and low coercivity, also known as soft magnetic ferrite core. Inductors or transformers can be made by winding coils on the ferrite core, and they are widely used in instrumentation, communication equipment and household appliances. Nantong Zhongxing Magnetic industry produces ferrite core materials of many brands, geometric shapes are also varied, including ET core, ER core, EV core, T core, EP core, RM core, PQ core and so on.

ferrite core is a kind of high frequency magnetic conductive material (the principle is the same as silicon steel sheet, but used in high frequency environment), mainly used as high frequency transformer (such as switching power supply, line output transformer, etc.), high frequency magnetic ring (anti-interference), etc., increase the permeability, improve the inductance quality factor, transformer inside. To give full play to the performance of ferrite core, the following precautions are very important:

First, the effect of ferrite magnetic ring is related to the circuit impedance: the lower the impedance of the circuit, the better the filtering effect of the ferrite magnetic ring (magnetic ring specification). Therefore, in the general product manual of ferrite materials, the insertion loss of ferrite materials is not given, but the impedance of ferrite materials is given, and the greater the impedance of ferrite materials, the better the filtering effect.

Second, the effect of current: When a large current flows through the wire of the soft magnetic ferrite core, the low frequency insertion loss of the filter will become smaller, and the high frequency insertion loss will not change much. To avoid this, when used on the power cord, the power cord and the power return line can be passed through the ferrite at the same time.

Third, the choice of ferrite magnetic ring materials: according to the frequency of interference to be suppressed, select ferrite materials with different permeability. The higher the permeability of ferrite material, the larger the impedance of low frequency and the smaller the impedance of high frequency.

Fourth, the number of soft magnetic ferrite core on the cable: Increasing the number of ferrite magnetic rings on the cable can increase the low-frequency impedance, but the high-frequency impedance will be reduced. This is due to the increase in parasitic capacitance.

Fifth, the determination of the size of the ferrite magnetic ring: the greater the difference between the inner and outer diameters of the magnetic ring, the longer the axial direction, the greater the impedance. But the inside diameter must enclose the wire. Therefore, to obtain large attenuation, try to use a larger magnetic ring with the inner diameter of the ferrite magnetic ring enclosing the wire.

Sixth, the installation position of ferrite magnetic ring: generally as close as possible to the source of interference. For cables on a shielded chassis, keep the magnetic ring as close as possible to the inlet and outlet of the cables on the chassis.

7. The effect is better when used with capacitive filter connectors: because the effect of ferrite magnetic ring depends on the impedance of the circuit, the lower the impedance of the circuit, the more obvious the effect of the magnetic ring. Therefore, when the original cable is installed at both ends of the capacitive filter connector, its impedance is very low, the effect of the magnetic ring is more obvious.