Inductor is a kind of circuit element, which will produce electromotive force due to the change of passing current, so as to resist the change of current. The structure of inductor is similar to that of transformer, but there is only one winding, which is generally composed of skeleton, winding, shield, packaging material, magnetic core or iron core.

If the inductor is in the state of no current, it will try to prevent the current from flowing through it when the circuit is connected; If the inductor is in a state of current flow, it will try to keep the current constant when the circuit is disconnected.