Inductor is an element that can convert electric energy into magnetic energy and store it. The structure of inductor is similar to that of transformer, but there is only one winding. Inductor has a certain inductance, which only prevents the change of current. If no current passes through the inductor, it will prevent the current from flowing through the inductor; If a current flows, it will try to keep the current constant when the circuit is disconnected.

Inductance in the circuit mainly plays the role of filtering, oscillation, delay and notch, as well as shielding signals, filtering noise, stabilizing current and suppressing electromagnetic interference. The most common function of inductance in circuit is to form LC filter circuit with capacitance. Capacitors have the characteristics of "DC resistance and AC resistance", while inductors have the functions of "DC resistance and AC resistance". If the DC with more interference signals passes through the LC filter circuit, the AC interference signal will be converted into heat energy by the capacitor and consumed; When pure DC current passes through the inductor, the AC interference signal in it is also converted into magnetic induction and heat energy, and the higher frequency is most easily impedance by the inductor, which can suppress the interference signal with higher frequency.

Inductor has the characteristics of preventing alternating current from passing and allowing direct current to pass smoothly. The higher the frequency, the greater the coil impedance. Therefore, the main function of inductance is to isolate and filter AC signals or form a resonant circuit with capacitors and resistors.