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With the rapid development of the current technology, more and more electronic products will use common mode filter inductors, so how to choose the amount of its sensitivity?

Changzhou South Electric Component Factory Co., Ltd. engineers say this to everyone!

First, how to choose the inductance of the common mode filter inductor?

The common mode inductor, also known as the common mode choke coil, is the opposite of the winding direction of a closed magnetic ring inductor, and the same common mode choke, the ideal common mode choke It has an obstructive effect on common mode interference between L and N, and has no inductance suppression effect on the differential mode inductance between L and N. However, if the incomplete symmetry of the inductor winding is actually caused by the differential mode leakage inductance, the power supply current flows in the opposite direction when the two windings flow in opposite directions, and the magnetic flux cancels out, which is low impedance. The power supply current flows in the same direction when flowing through the two windings. At this time, the magnetic flux is added to be high impedance, which reduces the common mode noise.

1, common mode filter inductor

Common mode inductor is an important part of equipment used in mobile power, switching power supply, etc. Working principle: When current flows through two coils with opposite winding directions, two mutually canceling magnetic fields h1, h2 are generated. It is mainly affected by the ohmic resistance of the inductor and the damping of the small leakage inductance at the operating frequency that can be omitted. If an interference signal flows through the coil, the coil exhibits high impedance and a strong damping effect, which achieves the effect of weakening the interference signal.

Manufacturers will consider the filter band curve when selecting the common mode filter inductor. The larger the impedance of the common mode, the better, and pay special attention to the influence of differential mode impedance on the signal, pay attention to the high speed port. When the rated current is large, the wire diameter of the common mode inductor is also increased to withstand a larger current. In addition, in order to reduce the characteristics of the low frequency, it is possible to maintain an appropriate increase in inductance.

Second, the common mode filter inductor's sensitivity selection formula?

Answer two: According to the formula L = AL × N2 (inductance = inductance coefficient × number of turns 2)

Therefore, the inductance of the filter inductor is related to the inductance in addition to the number of turns, but the inductance is related to the material of the core!

Like the filter UU type and EE type, generally use high-conducting magnetic core, according to your test results, calculate the AL value of the core according to the formula L = AL × N2, to understand the core material.

UU16: 50T=17mH, then AL≈6800nH/N2

EE35: 120T=15.6mH then AL≈1080nH/N2

The material value can be determined from the AL values of the two cores. The UU16 should be a high-conducting core R12K-15K, and the EE35 is a power-type core (but the core AL is too low, normal EE35 power type). For example, PC40 has more than 3000)

The inductance of the common-mode filter inductor is a very important factor for manufacturers to choose, so how to choose the size of the inductor has a great impact!

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