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Filter Inductor Frequency Characteristics

Oct 18, 2017

Filter Inductor Frequency characteristics

Filter Inductor Design Considerations

The frequency characteristics of the filter inductor are mainly affected by three factors

A, the core material loss is the most important, it leads to Q value from the maximum after the negative slope.

B, dielectric loss is also a factor in the impact, especially in the high frequency band is particularly evident.

C, the third influencing factor is the self-resonant effect of distributed capacitance and inductance.

The self-resonant frequency has a negative effect on the performance of the filter inductor. The self-resonant frequency is determined by the distributed capacitance and self-inductance, and the distributed capacitance is determined by the winding method. Minimizing the distributed capacitance is a very important consideration in winding design. For the winding of the toroidal core, its effective capacitance is in parallel with the inductor, which is the sum of the capacitance between the line and the line, between the layer and the layer and between the winding itself and the magnetic core.

Good winding design technology is to try to reduce the number of turns between the voltage, and strive to minimize the distribution of capacitance, such as the winding is divided into several groups, or the use of winding row can effectively less capacity. In the winding and internal segment connection technology, should try to avoid the input and output side by too close, because in the two parts with the circle between the maximum potential energy, and thus the distribution of the largest effective capacitance. At the same time, the humidity index and potting and packaging materials, the insulation constant will increase the distribution of capacitance.

For precision winding core, it is required to have good time stability and good temperature reproducibility. So in its temperature cycle, the winding stress must be released. In the case where the magnetic core is wound around the coil, it must be done as much as possible from the chamber to the temperature of 125 ° C. This temperature cycle is not only to release the stress, but also to remove the role of humidity, when the completion of the temperature cycle, The final adjustment of the inductance of the filter inductor.

After winding the core must be kept dry, as soon as possible soaked, potted or sealed up, should be carefully selected potting compound material to avoid some of the material with time and temperature shrinkage, and affect the stability. The addition of some padding material to the outside of the winding core can improve this effect.

For the design engineer, it is important to understand the conditions under which the thermal aging causes the core loss to increase. Under high frequency conditions, eddy current loss is the main loss, while the low frequency, the magnetic leakage loss is the main loss. And the proportion of the various losses in the total loss will also be affected by the magnetic flux density. The effect of high temperature thermal aging is the eddy current portion of the core loss.

The use of an open air gap in the ferrite core reduces the effective permeability of the core, thereby reducing the working magnetic flux density, but this air gap can cause severe localized air gap losses, Above 100KHz, especially in many cases, the air gap loss will exceed the core loss, because the magnetic core air gap is evenly distributed, so this type of localized air gap loss is basically not exist.