What is an EMI Filter?
EMI filters, also called EMI suppression filters, are an effective way to protect against the harmful impacts of electromagnetic interference. What does an EMI filter do? When attached to devices or circuits, EMI filters can suppress electromagnetic noise transmitted through conduction. These filters extract any unwanted current conducted through wiring or cables, while allowing desirable currents to flow freely. EMI filters that suppress noise from grid power are also called EMI power line filters.
How do EMI filters work? Most electromagnetic noise is in a higher frequency range, so EMI filters are often low-pass filters that sift out high frequencies while letting lower frequencies pass through. Different EMI line filters suppress specific frequencies of noise, while allowing others to flow unimpeded. After the filtering process, electromagnetic noise gets diverted away from the device and to the ground. Some EMI filters may also route unwanted currents back to the noise source or absorb them.
Most electronics contains an EMI filter, either as a separate device, or embedded in circuit boards. Its function is to reduce high frequency electronic noise that may cause interference with other devices. Regulatory standards exist in most countries that limit the amount of noise that can emitted.