An inductor is a passive electronic component that builds up an electromagnetic field, which can store energy. Inductors see frequent use in power circuits or to reshape alternating current based signals. An SMD inductor, or surface mount device inductor, is a model of inductor that has no wire leads on its ends. This type of inductor is mounted directly to the surface of a circuit board via a metal pad on either end of the device.
An SMD inductor is commonly constructed of a small coil shaped much like a spring and made of an electrically conductive wire. In some models of inductors, a core of some type is present in the center of the coil. Depending on the material chosen to serve as a core, often ferrite based, and the size and density of the core itself, the operational properties of the coil can be altered to fit specific needs.
When an electrical current passes through the coil, an electromagnetic field builds between its turns. This field tends to oppose directly any change to the electrical current that created it. Due to this tendency, a simple SMD inductor often finds use in a power circuit to prevent changes in voltage or current from passing through the circuit and on to other electronic components. An inductor used in this way is referred to as a choke and is part of a power circuit’s filtering assembly.
Inductor operational principles depend on the operational principles of the electromagnetic field they create. Once the field is built in an inductor, any change to the current or voltage that sustains that field causes a magnetic flux to occur. This flux will induce a new voltage, which will exist within the field and in direct opposition to the voltage attempting to pass through the field. The effect of inducing a new voltage is called inductance, from which the inductor derives its name.
An inductor’s ability to generate inductance is measured in a unit called a henry. The basic description of a henry is 1 volt induced for every 1-ampere change in the current through the coil per second. Depending on the intended use of the inductors in question, their ratings can vary from millionths of a henry to many henrys. An SMD inductor that will be part of a circuit board assembly is typically rated toward the lower end of this range. Physically small, it most often is used to control and filter relatively small electrical signals.