The core operation of an LCA^® EMI filter is based on its low-pass filtering characteristic. It functions like a “traffic controller” in the frequency domain, prioritizing the passage of low-frequency “useful signals” (such as 50/60 Hz AC power) while strictly blocking high-frequency “noise vehicles.”

        An internal network of inductors and capacitors works in concert to achieve this task: the inductors present high impedance to high-frequency noise, blocking its path, while the capacitors provide a low-impedance shunt path, diverting the noise to ground or back to its source. This effectively separates the noise from the clean signal.

        However, a key limitation is that this filter primarily targets conducted noise propagating along the conductors. It is inherently ineffective against noise propagating as radiated emissions through free space. Furthermore, the filter’s own unshielded housing and leads can even become secondary sources of radiation. Therefore, in practical engineering, EMI filters must be combined with metal shields to form a complete defense line—the filter handles conducted interference, while the shield contains radiated interference. The filter can only perform adequately as a standalone solution when the noise source is very close to it, and the intervening wiring is sufficiently short. Otherwise, unaddressed radiated noise can easily re-couple onto the already filtered lines, negating the filter’s effect.

——2025.9.27