Electronics > Projects, Designs, and Technical Stuff
Conducted emissions conundrum
colsramble:
--- Quote from: TimFox on August 05, 2020, 05:04:18 pm ---In what frequency range are your excessive conducted EMI voltages? Cheap line filters are effective above maybe 1 MHz, but there are (more expensive) units that are effective at lower frequencies.
--- End quote ---
Noise is sub 1Mhz - mostly 300-800Khz which, as you say, is hard to get rid of easily/cheaply.
prasimix:
Welcome to club :). I can confirm that Mean Well or in my case combination of two models has some real issue with conducted emission (more details you can find here). Separately tested with a resistive load both pass tests properly.
If you have a spectrum analyzer on hand you just need LISN (ask @Jay_Diddy_B for details) and you can start with in-house testing.
Buying $300 ready-made filter is still no guarantee that it will helps in you case (I have tried many and none have helped). I'd suggest that you invest that money in different CM chokes, and assortment of X and Y caps and find your combination. If you succeed such a filter will require some extra PCB space but will be many times cheaper than any ready-made filter.
colsramble:
--- Quote from: prasimix on August 06, 2020, 06:21:47 am ---Welcome to club :). I can confirm that Mean Well or in my case combination of two models has some real issue with conducted emission (more details you can find here). Separately tested with a resistive load both pass tests properly.
If you have a spectrum analyzer on hand you just need LISN (ask @Jay_Diddy_B for details) and you can start with in-house testing.
Buying $300 ready-made filter is still no guarantee that it will helps in you case (I have tried many and none have helped). I'd suggest that you invest that money in different CM chokes, and assortment of X and Y caps and find your combination. If you succeed such a filter will require some extra PCB space but will be many times cheaper than any ready-made filter.
--- End quote ---
That thread makes for an interesting read as our configuration is somewhat similar. Unfortunately I don't have the equipment to test this locally so relying on remote 3rd party who have been trying various choke arrangements. The Meanwell supplies are external in-line adapters and we don't currently have the luxury of modifying or integrating them without a significant change to the overall system design. We've got a few alternate supplies on the way from our supplier in China so crossing our fingers atm!
TimNJ:
--- Quote from: jkostb on August 05, 2020, 06:07:35 pm ---I recently finished a product which had to comply with the EU medical device directive. This means it had to comply with IEC60601. The power supply was a Meanwell power supply (as yoiu probably guessed), because this was the cheapest medical power supply with very good specs. During EMC testing we discovered that the conducted emission was exceeded. During the design we had paid special attention to EMC, board layout and filtering. All power supplies were heavily filtered with common mode chokes, ferrites etc. We suspected that the root cause must be in Meanwell power supply, so we asked Meanwell to share EMC test report. Meanwell was not willing to co-operate. For this reason we replaced the power supply with a TDK-Lambda power supply and retested the product. This time our product passed the EMC test for IEC60601 with a large margin for conducted emission! I suspect that Meanwell test their product with a resistive load during EMC test. This is of course not realistic if your product contains switching regulators. Later I opened a meanwell power supply and compared it to a TDK-Lambda power supply. The TDK lambda power supply was 2x times more expensive but the build quality, filtering was a lot better.
--- End quote ---
Resistive load is the standard way power supply manufacturers test emissions. It would be quite unlikely that TDK was using some “other” kind of load. I believe Meanwell does a lot of “self-certification”, so that may have some influence...if you catch my drift. Also check the footnotes in the EMC section. May say something like “Needs 500x500mm metal plane and King Core PNxxxxx ferrites on input to pass Class B emissions.”
Mr. Scram:
--- Quote from: jkostb on August 05, 2020, 06:07:35 pm ---I recently finished a product which had to comply with the EU medical device directive. This means it had to comply with IEC60601. The power supply was a Meanwell power supply (as yoiu probably guessed), because this was the cheapest medical power supply with very good specs. During EMC testing we discovered that the conducted emission was exceeded. During the design we had paid special attention to EMC, board layout and filtering. All power supplies were heavily filtered with common mode chokes, ferrites etc. We suspected that the root cause must be in Meanwell power supply, so we asked Meanwell to share EMC test report. Meanwell was not willing to co-operate. For this reason we replaced the power supply with a TDK-Lambda power supply and retested the product. This time our product passed the EMC test for IEC60601 with a large margin for conducted emission! I suspect that Meanwell test their product with a resistive load during EMC test. This is of course not realistic if your product contains switching regulators. Later I opened a meanwell power supply and compared it to a TDK-Lambda power supply. The TDK lambda power supply was 2x times more expensive but the build quality, filtering was a lot better.
--- End quote ---
It surprises me Meanwell isn't sharing the tests reports freely, let alone upon request. If they can't pass EMC testing or prove it they're not much better than any other generic unbranded outfit. I really thought better of them as they're reasonably well regarded.
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