May 12, 2008 What is an inductor? How do inductors behave? How do you protect against inductive kick-back? Inductors are closely related to capacitors; the rate of current change in an inductor depends on the voltage applied across it, whereas the rate of voltage change in a capacitor depends on the current through it. The symbol and defining equation for an inductor is where L is called the inductance and is measured in henrys (or mH, uH, etc.) and "di/dt" is the change in current over a small period of time. Putting a voltage across an inductor causes the current to rise as a ramp (for a capacitor), supplying a constant current causes the voltage to rise as a ramp; 1 volt across 1 henry produces a current that increases at 1 amp per second) The symbol for an inductor looks like a coil of wire; that's because, in its simplest form, that's all it is. Variations include coils wound on various core materials, the most popular being iron (or iron alloys, laminations, or powder) and ferrite, a black, nonconductive, brittle magnetic material. these are all ploys to multiply the inductance of a given coil by the "permeability" of the core material. The core may be in the shape of a rod, a toroid (doughnut), or even more bizarre shapes, such as a "pot core" (which has to be seen to be understood). Inductors find heavy use in radio frequency (RF) circuits, serving as RF "chokes" and as parts of tuned circuits. A pair of closely coupled inductors form the interesting object known as a transformer. An inductor is, in a real sense, the opposite of a capacitor. Back to FAQ home page