Re: Modifiying an offline LED driver PCB with EMC components on "flying wires"
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Another point is that we would like to experiment with different values of diff mode inductors. As such, how good (or bad) a practice would it be to have these diff mode inductors coming out on flying wires so that we can change value quickly and take a fresh conducted mode scan?
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Also, suppose we depopulated the entire EMC filter of the offline SMPS….(the section upstream of the mains rectifier bridge), and then made one using the same components, but on a piece of stripboard, and then wired this stripboard into the PCB, (so it again had a filter) how much different would the scan of the top post be, when dont with the "replacement" stripboard filter?
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I think you can see what I am getting at here…….the situation of needing to vary the EMC filter components and then re-scan.
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Having to make a whole new PCB every time an EMC filter component is changed, and then re-EMC-scanning, is not terribly practical.
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Also, I have often seen offline SMPS EMC filters, with 22pF (or so) ceramic capacitors across the diff mode inductors. The purpose of these is to have a component that you can vary in order to reduce particular peaks on the conducted EMC scan. What do you make of this practice?
Also, at one company, they had done a 150W Boost BCM PFC stage, and across the boost inductor, they had a ~100pF ceramic capacitor in series with a ferrite bead. When asked about it, they simply said it failed if that was not there, so they were leaving it in. This was at a very large successful multinational TV company.