Filtering, delay, notch, oscillation, and so on image saying: "dc, ac resistance". In the electronic circuit, the action of ac finite current, it and resistor or capacitor can form high-pass or low-pass filter, phase shift circuit and resonance circuit, etc. The transformer can be used for AC coupling, voltage change, current change and impedance conversion. The role of patch winding inductance seems to be some opposite, we said that the capacitor is direct resistance, and the inductance is just the opposite, its role is direct resistance, originally! The direction of the magnetic field generated by the direct current through the inductor is the same and does not change.

**Two Main Functions Of Patch Power Inductor**

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**1. Inductance coil choke effect:**

Inductive coil The self-induced electromotive force in the coil is always resistant to the current change in the coil. Inductance coil has a blocking effect on ac current, the size of the blocking effect is called inductive reactance XL, the unit is ohm. Its relation with inductance L and ac frequency f is XL=2πfL. Inductors can be divided into high frequency choke coil and low frequency choke coil.

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**2. Tuning and frequency selection:**

An LC tunable circuit can be formed by an inductor coil in parallel with a capacitor. That is, the natural oscillation frequency of the circuit f0 is equal to the frequency f of the non-AC signal, so the inductive and capacitive reactance of the circuit are equal, so the electromagnetic energy oscillates back and forth in the inductor and capacitor, which is the resonance phenomenon of the LC circuit. When resonant, the inductive reactance and capacitive reactance of the circuit are equivalent to reverse, the total circuit current inductive reactance is the minimum, the current is the maximum (refers to the AC signal f=" F0 "), LC resonant circuit has the role of selecting frequency, can select the AC signal of a certain frequency F.

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