What are the EMC components used in designing an AC-DC power adapter?
The term safety is important in any electrical consumer product. Some of them include safety against thermal issues, mechanical safety, and Electromagnetic compatibility (EMC). All electronic devices have the potential to radiate and absorb Radio frequency (RF) energy. The principle behind EMC is that the equipment should limit itself from radiating below a specified level, and be able to withstand a certain outside level of incident RF radiation.
Typical components in an AC-DC Power adapter used to limit or withstand these electromagnetic interactions include:
Pi Filter or combination of x-cap with common mode filter at the AC input side.
A difference mode inductor in series on the line.
A snubber circuit to limit the MOSFET spike voltage and ringing effect.
A transformer with a shielding winding to the ground.
A Y-cap between the primary and secondary of the Flyback converter.
A bead core of MOSFET for reducing high frequency emissions.
Figure 1. EMC Components in PAG1P and PAG1S Type-C Power Adapters