In an effort to efficiently solve an EMI problem at its source, many OEMs are transferring, via power supply specifications, the conducted EMI requirements for their product to the power supply. Unfortunately, even when the power supply meets these stand-alone specifications, application experience has shown that an additional filter may be required at the point of entry for the AC power. Also, this enhanced EMI performance can add considerable cost and bulk to the power supply. An alternate approach is to use an individual filter located where it is most effective, at the point of entry for system power. This approach has an added advantage in systems with multiple power supplies. A single filter like the SE30 or SF30 can often replace multiple smaller units, reducing costs and minimizing system ground leakage current.

The system-level filter can also be used to comply with EMI requirements that exceed the original power supply EMI specifications. LF and LX Series filters are very effective in these applications, frequently allowing a power supply designed for FCC-level performance to meet CISPR/EN specifications.