STMicroelectronics 400 W FOT-controlled PFC pre-regulator with the L6563S EVL6563S-400W EVL6563S-400W Fiche De Données

   

   

   

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 Doc ID 15796 Rev 2

Differential mode currents in a circuit with high- and low-frequency components (like in a 
PFC) may produce audible noise due to inter-modulation between the operating frequency 
and the mains line frequency.

This phenomenon occurs because of the mechanical vibration of reactive components like 
capacitors and inductors. Current flowing in the winding can cause the vibration of wires or 
ferrite, and as such produce buzzing noise. To avoid this, the boost and filter inductors have 
to be wound with a correct wire tension and the component has to be varnished or dipped. 
Frequently, X-capacitors and filter capacitors after the bridge generate acoustic noise 
because of AC current that causes the electrodes to vibrate, producing buzzing noise. Thus, 
minimizing the AC current by inserting a differential-mode, Pi filter between the bridge and 
the boost inductor helps to reduce the acoustic noise. The EMI filter will also benefit from 
this. In fact, such a filter significantly decreases the ripple current that otherwise has to be 
filtered by the EMI filter. The capacitors to be selected are of a polypropylene (preferably 
dipped) type because boxed ones are generally more at risk of generating acoustic noise.