Switching Power Supplies A - Z

DM and CM Noise in Switching Power Supplies

The Main Source of CM Noise

By definition, if there is CM noise, there must be some leakage path to Earth. But in power

supplies this path is quite unlike what engineers in other fields may be talking about. For

example, in many power supplies, we often use the enclosure to provide us with a fortuitous

“infinite heatsink” with which to cool our power devices. We need some electrical insulation,

since the tab of the power device is usually the drain of the mosfet, and that point is usually

swinging. An insulator for such a purpose needs to be a poor electrical conductor, but a good

thermal conductor — so we