Power Inductors: How Their Electromagnetic Radiation Is Influenced
Electromagnetic radiation (EMR) is generated by inductors in power converters. This activity is important because of the surrounding components that can cause magnetic coupling, which allows for a magnetic field to transmit power from one shaft to another. Here's a quick look at how electromagnetic radiation is influenced within power inductors.
Effects of Shielding
An inductor is a coil with either a shield to block electromagnetic radiation or it is unshielded. Some inductors are semi-shielded. Shielded inductors are manufactured to house the coil within a container, whereas an unshielded inductor has windings exposed to a magnetic field. Semi-shields are made of epoxy resin, covering the wire. Engineers must balance between shielding and exposure to magnetic energy to reduce electromagnetic interference.
The start of a winding is just as important as how orderly and tight the coil is around the core. The start of winding is usually indicated with a dot on the inductor unit. This dotted end should be connected closer to the switch node, since it will generate the most interference. If the inductor is connected improperly, it may result in excessive electric or capacitive coupling.
Electromagnetic interference only exists with the presence of a source, medium or person. With an increase in switching frequencies, DC/DC converters reduce switching losses by automating faster rise and fall times. At the same time, it causes volatile switch node transitions and switch node ringing in the 100 to 200 MHz range. For this reason, it's imperative to select the proper inductor for EM compatibility. The key factors to consider are the inductor's core material and thickness, along with other inductor properties.
Electromagnetic radiation must be considered for guarding against electromagnetic interference and other power issues. So be sure to research power inductors prior to purchasing them to ensure that they are appropriate for the applications you need.