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Reasons for Requiring EMI Suppression Filters



Electromagnetic Interference (or EMI) is said to occur when an electronic device does not receive the intended current due to the interruption of unwanted electric currents. Such disruptive currents (also termed as Noise or Electromagnetic Noise) generate from any external source or any components of the device. 

Electromagnetic interference can be produced from various sources like AC motors, light dimmers, microprocessors, switch-mode power supplies, etc. It may disrupt the functioning of the device or lead to improper functioning of the device. Based on the level of disruption, EMI impacts the quality of the signal received by the device such as poor mobile networks. The severity of disruption leads to fatal consequences like failure or malfunction of medical equipment. The impact of EMI depends on several factors like interference duration, noise immunity of the device, etc.

EMI is mainly of two types namely 

  • Conducted EMI
  • Radiated EMI

In conducted EMI, noise travels through conductors such as wires, power lines, or electrical components (like resistor, capacitor, inductor). In radiated EMI, noise travels in free space in the form of magnetic/radio fields. Although there is a difference between the conducted and radiated EMI, both of them negatively impact the performance of the electronic device (system degradation, malfunctioning, or failure). 

EMI Suppression Filter & its Requirement

EMI Suppression Filter (also known as EMI filter) is an effective method to protect against the harmful effects of electromagnetic interference. The EMI suppression filter is attached to an electronic device/circuit to suppress the noise transmitted through conduction. The filter is used to extract the unwanted current conducted through wiring/cables and pass the desirable currents to flow freely. 

“EMI filter used in power grids to suppress the noise is known as EMI power line filters.”

EMI filters are usually low-pass filters as most electromagnetic noise has a high range of frequency. Such filters allow passing only low-frequency signals and suppress the high-frequency signals. Likewise, different EMI line filters suppress a specific range of frequencies and allow passing the rest of the frequencies. The electromagnetic noise extracted by the EMI filter then gets diverted away from the device and grounded. In some cases, EMI filters absorb the unwanted currents or route them back to the source.

EMI filters can only protect against conducted EMI. Such filters can still transmit noise in the air and damage the device. In order to protect against radiated EMI, EMI filters should be paired with shields.

Noise travels from one side of the EMI filter to the other by recoupling the wires. If a shield is attached to the EMI filter, it can effectively block all forms of electromagnetic interference. In case, the conductor between the filter and the source of EMI and EMI filter is small, only a filter is sufficient to suppress the electromagnetic noise.

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