Choosing an Input EMI / EMC Filter for a Power Supply

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There are two primary features that an enter EMI filter can carry out:

  1. Decrease outgoing electrical noise to keep away from interfering with neighboring tools
  2. Attenuate (cut back) incoming electrical noise that might harm the system

Relating to outgoing noise, though most power provides meet the governmental rules for EMI, noise is additive and if there are a number of power provides or high velocity processor boards, it may end up in a failing grade.

If the noise is simply barely out of specification, then a (decrease price) single stage filter might suffice. If the noise is significantly out of specification then a increased efficiency two stage filter will probably be required.

An instance of those can be Lambda’s RSEN (single stage) and RSHN (two stage) filters. Look for the phrases “wideband” or “low frequency attenuation” within the features.

Incoming electrical noise is normally within the type of a spike or burst of power. It may be generated from pure causes resembling a lightning storm or synthetic by a massive piece of business tools.

This sort of filter might have “high pulse attenuation” listed as a feature and may have internal values optimized to cut back these probably dangerous spikes from reaching the power provide. The filter will even have some outgoing noise attenuation, however will not be as efficient. An instance can be Lambda’s RSMN collection of filters.