Feature: EMI filters
Filtering common-mode noise in automotive environments
By Jeff Elliott, US-based technical writer T
here are many factors adding to interference in electronics, disturbing their functionality and even damaging them. Tightly packing
components into ever-shrinking spaces makes the situation worse, leading to signals interfering with each other. Today’s automobiles are a prime
example of growing electronics into smaller spaces: Wi-Fi, Bluetooth, satellite radio, GPS systems, LED lights, cameras and many on-board instruments are multiplying, as are numerous systems that use DC motors.
Prevention is better than cure To eliminate unwanted noise, the industry typically uses shielding, along with EMI filters in various configurations. But some of these traditional solutions are no longer sufficient, given increases in operating frequency and higher frequency noises that expand the affected frequency range. In addition, a growing number of devices are more easily affected by noise, even by weak energy
28 April 2022
www.electronicsworld.co.uk
fields, since devices nowadays operate at lower and lower voltages. Hence, OEMs are abandoning options such as two- capacitor differentials, three-capacitor (one X-cap and two Y-caps) solutions, feedthrough filters, common-mode chokes or combinations of these, in favour of more suitable solutions such as monolithic EMI filters that deliver superior noise suppression in substantially smaller packages.
EMI/RFI filters Strong electromagnetic fields can cause unwanted currents, causing interference or circuit malfunction.
EMI/RFI can be conducted or radiated.
In conducted EMI, noise travels along the conductors, whereas in radiated, noise travels through air as magnetic fields or radio waves. Even if the unwanted energy is weak, it
can mix with radio waves, causing reception loss, abnormal noise in sound, or disrupted video. Sources of noise can be natural, such
as electrostatic discharge or lightning, or artificial, such as contact noise, high- frequency device leakage, unwanted emissions (e.g. harmonic emission from digital circuits or switching power supplies), and others. Noise generated inside the circuit of an electronic device can acause interference with others in the same space. Usually, EMI/RFI noise is common-
mode noise, so the solution to eliminating unwanted high frequencies is an EMI filter, either as a separate or embedded device. Tis also helps OEMs meet the regulatory standards in most countries, which limit the amount of emitted noise. EMI filters normally comprise passive
EMI and RFI filters by Johanson Dielectrics
components, such as capacitors and inductors.
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