The total EMI is a combination of both Common mode and differential mode noise.When looking at the complete noise spectrum it is sometimes difficult to identify the individual noise sources.With the EMIfix network it is easy just to press the CM or DIFF button to identify whether the noise is Common mode noise or Differential…
Common mode noise is generated between Chassis and Primary.This is typically noise coupled in the transformer between the primary and secondary winding.It may also be noise coupled from the drain of a switch FET to a heatsink connected to Chassis.Or noise coupled to the shield of a motor cable, when high voltages are switched.The Common…
Differential noise is typically generated by the fast switch transients.In an AC/DC switch mode power supply the primary source for the differential noise is typically the PFC switch components.Capacitors must be placed correctly to reduce the loop for the switch currents and the switching must be done as “soft” as possible.The input switch currents can…