STMicroelectronics 100 W transition-mode PFC pre-regulator with the L6563S EVL6563S-100W EVL6563S-100W Data Sheet

Doc ID 16279 Rev 2

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The following figures show the peak measurement of the conducted noise at full load and 
nominal mains voltages for both mains lines. The limits shown in the diagrams are EN55022 
class-B which is the most popular regulation for domestic equipment using a two-wire mains 
connection. 

It is also useful to remind that typically a PFC produces a significant differential mode noise 
with respect to other topologies and therefore in case an additional margin with respect to 
the limits is required, we suggest trying to increase the across-the-line (X) capacitors or the 
capacitor after the rectifier bridge C5. This will be more effective and cheaper than 
increasing the size of the common-mode filter coil that would filter the differential mode 
noise by the leakage inductance between the two windings only.

In order to recognize if the circuit is affected by common mode or differential mode noise it is 
sufficient to compare the spectrum of phase and neutral line measurements.  If the two 
measurements are very similar, the noise is almost totally common mode. If there is a 
significant difference between the two measurement spectrums, their difference represents 
the amount of differential mode noise. Of course to get a reliable comparison the two 
measurements have to be done in the same conditions. If the peak measurement is used as 
in the figures below, some countermeasures will have to be used, like synchronizing the 
sweep of the spectrum analyzer with the input voltage. This is necessary with TM PFC 
having a switching frequency that is modulated along the sine wave.

Because the differential mode produces the common mode noise by the magnetic field 
induced by the current, decreasing the differential mode consequently limits the second one.