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# Why should we use inductor in circuit ?

2020-08-31 Basic functions: filtering, oscillation bai, delay, notch, etc.

The vivid statement: "passes direct current but resists alternating current"
Detailed explanation: In electronic circuits, the inductance coil acts on the AC current limitation. It can form a high-pass or low-pass filter, phase shift circuit and resonant circuit with resistors or capacitors; transformers can perform AC coupling, transformation, Variable current and impedance transformation, etc.
Knowing from the inductance XL=2πfL, the larger the inductance L and the higher the frequency f, the greater the inductance. The magnitude of the voltage across the inductor is proportional to the inductance L and also proportional to the current change speed △i/△t. This relationship can also be expressed by the following formula:
The inductance coil is also an energy storage element. It stores electric energy in the form of magnetism. The stored electric energy can be expressed by the following formula: WL=1/2 Li2.
It can be seen that the greater the coil inductance and the greater the flow, the more electric energy stored.
The most common role of inductors in circuits is to form an LC filter circuit together with capacitors. We already know that capacitors have the ability to "block DC and pass AC", while inductors have the function of "pass DC and block AC". If the direct current accompanied by many interference signals is passed through the LC filter circuit (as shown in the figure), then the AC interference signal will be consumed by the capacitor as heat; when the pure DC current passes through the inductor, the AC interference signal in it will also be It becomes magnetic induction and heat energy, and the higher frequency is most easily impedance by the inductance, which can suppress the higher frequency interference signal.
LC filter circuit
The inductance in the power supply part of the circuit board is generally made of a very thick enameled wire wrapped around a round magnetic core coated with various colors. And there are usually several tall filter aluminum electrolytic capacitors nearby. The two constitute the above-mentioned LC filter circuit. In addition, the circuit board also uses a large number of "snake lines + chip tantalum capacitors" to form an LC circuit, because the snake line folds back and forth on the circuit board, which can also be regarded as a small inductor.

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