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    Modifying a 60W offline SMPS PCB to achieve a pass in conducted EMC

    Hi,
    We needed to get a PCB (version 2) made up of our 60W Offline Flyback (PFC’d) LED driver. We needed it quickly so that our software engineer had something to work with.
    I couldn’t fit all the components on the PCB, therefore, I stole room from the AC filter part of the board, to give to other parts of the circuit. Now , as expected, this PCB fails EMC.
    Attached is the EMC filter schematic, and a picture of the EMC filter on the PCB, showing how tightly close together the AC filter components are. (AC filter part is outlined in light blue)

    However, this is the only board that we now have for the purposes of optimising the EMC filter….in other words, we must repeatedly modify this board and repeatedly put it back through conducted EMC testing, until we get a pass. In the EMC test, I will have to de-solder some of the small 22nF X2 capacitors and replace them with bigger ones, (220nF) wired into their pads with twisted “flying wires”. Obviously this is less than ideal. How much extra problem with high frequency common mode emissions do you think that such a “flying wire” modified EMC filter will give us?

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  2. #2
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    Re: Modifying a 60W offline SMPS PCB to achieve a pass in conducted EMC

    You are trying to pass EMC testing with a piece-of-crap design? A design that you already KNEW would fail? What kind of company do you work for? Please tell me the name so that I never, ever buy anything from you. This is stupendously poor engineering.



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  3. #3
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    Re: Modifying a 60W offline SMPS PCB to achieve a pass in conducted EMC

    Thanks, well, supposing i remove two 22nF X2 capacitors, and replace then with 220nF X2 capacitors, that are "flying wired" into their pads.....and then supposing we then pass conducted EMC.....then that is a good and worthwhile result.
    What i am wondering is, ...but then supposing i do this and we dont pass EMC, but the failure in that case is due to the exacerbation of higher frequency common mode emissions effects....then that does really point to the fact that we need to go to the considerable expense of producing another PCB for the EMC test.

    Version 1 of this board very very nearly passed conducted EMC......but as i discussed, we needed version 2 for the software person and so had to "steal" some of the space taken by AC (EMC) filter components.

    The top post of this thread shows just how close we were to passing conducted EMC with version 1 of this board...
    https://www.edaboard.com/showthread....d-Radiated-EMC



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