STMicroelectronics 250W TRANSITION-MODE PFC PRE-REGULATOR WITH L6563S EVL6563S-250W EVL6563S-250W Data Sheet

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Doc ID 16849 Rev 2

Figures 

, and 

 show the measurement in average mode 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 standard for domestic equipment 
using a two-wire mains connection. 

It is worth remembering that typically a PFC produces a significant differential mode noise 
with respect to other topologies. In case an additional margin, with respect to the limits, is 
needed, increasing the differential attenuation by increasing the across the line (X) 
capacitors or theC4 capacitor after the rectifier bridge is suggested. Sometimes a differential 
mode coil connected as a pi-filter placed after, between the bridge rectifier and the boost 
stage, is more effective and cheaper than increasing the size of the common mode filter coil 
which would filter the differential mode noise by the leakage inductance only between the 
two windings.

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 under the same conditions. 

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

As visible in the diagrams, in all test conditions there is at least a 6dB margin of the 
measurements with respect to the limits. The measurements have been done in AVG 
detection to evaluate the benefit of the jittering effect of the TM control.