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# How to analyze the selected value of magnetic ring inductance? Basic principle of common mode inductance

2021-12-17

Explain in detail how to analyze the selected value of magnetic ring inductance? What is the basic principle of common mode inductance?

How to calculate the selected value of magnetic ring inductance?

We can see that many penyou don't know much about the calculation of magnetic ring. For modern metal material soft magnetic magnetic particle flaw detection core winding inductance, the calculation method is as follows:

L=（4 × π ×μ× N × N × A）/l

μ Is the permeability,

N is the number of winding turns

A is the reasonable magnetic cross section

L is the reasonable equivalent circuit length

When you select the transformer skeleton, the manufacturer will show the main parameters. Many people think that the final result is based on this calculation formula, but the measured inductor quantity after the real winding is connected to the power supply is different from the calculated result. There is an important area, that is, when the current increases, the magnetic field intensity expands, The number of inductors will decrease with the increase of magnetic field strength (caused by the increase of current). There is no fixed formula to calculate the number of inductors,

When you select the transformer skeleton, the manufacturer will show the main parameters. Many people think that what is given according to this calculation formula is the final result, but the measured inductor quantity after the real winding is connected to the power supply is different from the calculated result. There is an important area, that is, when the current increases, the magnetic field intensity expands, The number of inductors will be reduced, This increases with the increase of magnetic field strength There are few inductors (caused by the increase of current) and there is no fixed formula calculation, which leads to inconvenience in the design process. At this time, we can only look at the trend chart of raw materials presented by the manufacturer; the trend charts of magnetic particle flaw detection cores of ferrosilicon, ferrosilicon aluminum, ferronickel and nanotechnology ferrosilicon materials are different, and only query the magnetic field strength caused by relative current at this time Percentage of inductor quantity that can be achieved by matching weather.

After the plan, we should also eliminate the enterprise

（4 × π ×μ× N × N × A）/l/10^3=※ μ H（4 × π ×μ× N × N × A）/l/10^6=※mH

Formula calculation of permeability, it is proposed to select a specific reasonable permeability!

When the permeability is not selected, there should also be calculation errors.

When the detection frequency is different, the permeability size is different,

Under different magnetic field strength, the specific permeability is also different

The wire diameter of winding cable is not different,

The winding affinity level is not different,

The detection method is not different,

Inductor values will also vary greatly!

Many years ago, when I expressed the influencing factors endangering the inductor value of electromagnetic coil winding to some friends, I took and placed a thin rope and thick line, and wound the same number of turns, and then tested and compared the inductor value in the middle of two groups of winding wires. The difference may be above 10%!

Apply the same cable diameter wire wrapped coil inductance on the magnetic ring with a small number of turns, one is close winding and the other is symmetrical sparse winding. Sometimes the difference between the two inductors is more than 10%!

Therefore, sometimes the transformer skeleton manufacturer will indicate in his instructions that his transformer skeleton is tested by a certain test standard under the application of a certain actual cable diameter, number of turns and winding method.

What is the principle of common mode inductance?

Why can common mode inductors prevent EMI? To understand this, we must analyze the structure of common mode inductor at the beginning.

When you select the transformer skeleton, the manufacturer will show the main parameters. Many people think that what is given according to this calculation formula is the final result, but the measured inductor quantity after the real winding is connected to the power supply is different from the calculated result. There is an important area, that is, when the current increases, the magnetic field intensity expands, The number of inductors will decrease with the increase of magnetic field strength (caused by the increase of current). There is no fixed formula to calculate the number of inductors,

Common mode inductor filter circuit, La and LB are common mode inductor electromagnetic coils. The two electromagnetic coils are wound on the same transformer core, The coil turns and phase difference are the same (in the opposite direction of the coil inductance). In that way, when all normal currents in the power supply circuit flow through the common mode inductance, the currents cause electromagnetic fields in the opposite direction in the inductance of the coil inductance with the same phase difference and offset each other. At this time, all normal data signal currents are mainly endangered by the coil resistance (and vibration reduction caused by a small amount of leakage inductance); when a common mode current flows through the electromagnetic coil, due to the isotropy of the common mode current, it will cause electromagnetic fields in the same direction in the electromagnetic coil and expand the inductive reactance of the electromagnetic coil, so that the electromagnetic coil mainly shows high characteristic impedance, resulting in strong vibration reduction effect. Therefore, the attenuation coefficient common mode current can achieve the purpose of the filter.

In fact, if one end of the filter circuit is connected with the interference signal and the other end is connected with the affected machine equipment, La, C1, LB and C2 form two groups of low-pass filters, which can control the common mode EMI data signal on the route at a very low pulse signal. The power supply circuit can not only inhibit the transmission of external EMI data signals, but also attenuate the EMI data signals caused by the route itself, which can reasonably reduce the impact of EMI on the compressive strength.

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