This is entry #3 of my 52 Project 2012: Foundational Electronic Components Crash Course series.
What is an inductor?
An inductor is basically just a coil of wire. It behaves differently from a regular wire because it is specifically coiled (often around a special material in the center), and this allows the electrical current to build up a magnetic field. This magnetic field affects the flow of current through the inductor such that it resists changes to the energy flowing through it.
How does an inductor work?
Inductors, like resistors and capacitors, have two terminals. Remember that resistors reduce the energy flowing through them by converting some into heat, and capacitors store the energy flowing into them with metal plates and special dielectric materials. Inductors, by contrast, resist any change in the flow of energy through them.
For an analogy, consider a flywheel. If the flywheel is not spinning, it takes effort to make it spin. If it’s already spinning quickly, it takes effort to make it stop. But whether the flywheel is stopped or spinning freely, it only takes effort to change its rotational speed (assuming a frictionless system, anyway). A flywheel stores rotational energy using momentum. Similarly, an inductor stores electrical energy in a magnetic field. Using the flywheel as an analogy, the inductor is “spinning” when it has built up a magnetic field, and it is “stopped” when there is no field.
When energy flows through the inductor, most of that energy goes into the creation of the magnetic field until it is fully charged. Once this happens, energy flows easily through the inductor as though it were a regular wire. Then, when the energy supply is cut off, the charged magnetic field is gradually converted back into electrical energy until the magnetic field is entirely gone.
So, to recap so far:
- A resistor reduces the flow of energy by converting it into heat.
- A capacitor stores energy in an electric field.
- An inductor stores energy in a magnetic field.
The magnetic field is able to build up in an inductor because of the placement, coil spacing, cross-section size, and central material used in the inductor. Inductance increases with the number of coils, as well as with the use of certain materials (such as iron).
Inductors in electronic circuits are often very, very small. However, sometimes, they are much larger than you might expect. Traffic signals use large wire inductors built into the road. The large metal chassis of a car sitting over the wire loops change the inductance value, and this change is detected by the traffic signal system.
Inductor ratings
Inductance is measured in henries, or sometimes in millihenries or nanohenries. One henry is defined as a one-amp-per-second rate of change of current that generates one volt. A little complex, yes, but think of it this way: more inductance means a stronger magnetic field will be generated.
Inductors have a maximum current rating, which is the maximum safe current the inductor can take without any potential damage.
Inductors also have a tolerance rating, specified as a percentage. The tolerance indicates by how much the actual performance may differ from the rated performance (similar to resistors and capacitors).
For a description of this 52 Project series and links to the all existing entries, go to the 52 Project 2012: Foundational Electronic Components Crash Course page.