Hiper-PFS heatsink connected to primary ground or earth
Posted by: treez
on
In an offline Hiper-PFS 4 PFC, , do you agree, its better to connect the FET heatsink to primary ground rather than earth? (Wouldn’t common mode EMC be worse if it was connected to Earth?)
(Obviously with a thin insulation pad between case and heatsink)
Also: Same question as above but for the Boost PFC TO220 diode?
FSCQ1565 datasheet
https://www.onsemi.com/pub/Collateral/FSCQ1565RT-D.pdf
Primary return connection is better for EMI. If you are using a separate TO220 output diode, it is also a good idea to counter-bore the heat sink hole so that you can use a shoulder washer with a longer shank for extra creepage between the screw/ diode heat sink tab and primary return. The standard TO-220 shoulder washer and sil pad approach does not provide sufficient creepage between screw and heat sink.This will also require a sil pad with a slightly larger through hole to accommodate the longer shank on the shoulder washer. Both the longer shoulder washer and the pad with larger holes are available as catalog items.