There are two primary functions that an input EMI filter can perform:

1. Minimise conducted emissions to avoid interfering with neighbouring equipment
2. Attenuate incoming electrical noise that could damage the system

Regarding conducted emissions, although most power supplies meet internationally recognised regulations for EMI, noise is additive and if there are multiple power supplies with noise generating loads such as high speed processor boards, it can result in the end equipment exceeding allowable limits.

If the noise is only slightly out of specification, then a (lower cost) single stage filter may suffice. If the noise is considerably out of specification then a higher performance two stage filter will be required.

To find out more, please visit the TDK-Lambda AC-DC Power Supplies FAQs page

If you have a question you’d like to ask TDK-Lambda, please feel free to use the online FAQ form and we’ll get back to you with an answer to your question as soon as possible.