I've been working on getting my 120W current-mode SMPS to pass the
conducted EMC test. The switching freq is 100kHz and has two stages PFC
and PWM integrated in one controller the ON Semi NCP1603. I've tried
different filter combinations but unfortunately each combination only
works for one load condition. For example:
1) when I have two common-mode choke and some X2 and Y2 capacitors that
gave me a good conducted EMI result, but only with <10% load.
2) Another combination with 2 ferrite beads in series, each for the active
and neural like before the common-mode choke gave me a good result at full
load.
3) When I added a aluminium heatsink/base to the board, none of the above
filters work. The conducted noise level shoot up at about 10MHz -15MHz
range.
Anyone has any idea on how I should tackle this problem? Or does anyone
know of any good design resources (books or website) that gives good
practical advice on EMI filter design for SMPS? I have millions of
questions in my head that I need answers for. Frustrating....grrrh!
