What is the function of an inductor?

Basic functions : Filtering, oscillation, delay, notch filtering, etc.

A vivid description : "Allow direct current (DC) to pass through, while blocking alternating current (AC)."

Detailed explanation : In an electronic circuit, an inductor coil has a current-limiting effect on alternating current. It can form high-pass or low-pass filters, phase-shifting circuits, and resonant circuits, etc., together with resistors or capacitors. A transformer can be used for AC coupling, voltage transformation, current transformation, and impedance transformation, etc. According to the formula for inductive reactance  \(X_L = 2\pi fL\) , the larger the inductance  L and the higher the frequency  f , the greater the inductive reactance. The magnitude of the voltage across this inductor is proportional to the inductance  L , and also proportional to the rate of change of current  \(\Delta i/\Delta t\) .

An inductor coil is also an energy storage element. It stores electrical energy in the form of magnetism, and the amount of electrical energy stored can be expressed by the following formula: WL=\frac{1}{2}Li^2\) . It can be seen that the larger the inductance of the coil and the larger the current flowing through it, the more electrical energy is stored.

The most common function of an inductor in a circuit is to form an LC filter circuit together with a capacitor. As we already know, a capacitor has the ability to "block DC and allow AC to pass through", while an inductor has the function of "allowing DC to pass through and blocking AC". If a direct current with many interfering signals passes through an LC filter circuit, then the AC interfering signals will be converted into heat energy and consumed by the capacitor. When the relatively pure direct current passes through the inductor, the AC interfering signals in it are also converted into magnetic induction and heat energy. The signals with higher frequencies are most easily impeded by the inductor, which can suppress the interfering signals with higher frequencies.

The LC filter circuit : The inductor in the power supply part of a circuit board is generally made of enameled wire with a very thick wire diameter wound around a circular magnetic core painted with various colors. And there are usually several tall aluminum electrolytic filter capacitors nearby. These two components form the aforementioned LC filter circuit. In addition, the circuit board also widely uses "serpentine traces + surface-mounted tantalum capacitors" to form an LC circuit. Since the serpentine traces wind back and forth on the circuit board, they can also be regarded as a small inductor.

Unit conversion of inductance :