..they obviously can't accommodate and test in every situation that the customer will use it in!)
Thanks, I agree, so why bother to put the OEM PSU module in a metal enclosure when testing it for radiated emissions? (as they have done)
I believe we would agree, that the main reason the following offline PSU's are in metal cases is so they pass radiated emissions testing
https://www.meanwell.com/productSeries.aspx?i=16&c=6#tag-6-16(the holes designed to allow ventilation but small enough to block below a certain wavelength of radiated emission)
In this , i am speaking of hard switched offline SMPS, not resonant ones.....(as you know, all offline SMPS > 75W have a hard switching boost pfc in, which even if quasi resonant, hard switches at turn off time....and isnt completely soft at turn on.)
I once worked for a company who had designed a world beating product, powered by an offline PSU in a plastic case, bought from China…..but couldn’t pass radiated EMC with it. They never realised that they only had to metal foil line the plastic case to pass radiated EMC……….they ended up selling the company off……..when I got there , I could see the signs of their desperation to pass radiated emc…they had purchased a super expensive near-field radiated emissions test apparatus….and they had a large device bolted to a bench, which they had been using to crack open other peoples offline plastic PSUs…so they could see what they weren’t doing to pass. But they never realised in time…and so came the sell off……all for the sake of a bit of metal foil lining!
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Hi,
...Its quite a situation with radiated emissions for offline SMPS. If your company's product is powered by an offline SMPS...then go onto your co's hard drive and fish out the offline SMPS's radiated emissions scan graphs....
....Thats right....you wont be able to find them.
These radiated scans are one of the deepest secrets of the company...only the owner and his most trusted staff will be allowed access to these scans.
The cost of a radiated emissions test is enormous...the cost of buying the test kit yourself (chamber etc) is totally unaffordable to most companys.
Ever offered to go along to the radiated emissions lab and carry out radiated emissions pre-compliance or compliance testing of your company's offline SMPS?.....you wouldnt have been allowed to go and do it.
Only the owner , or most trusted few, will be allowed to go and do it. If they dont know how to do it, then i find they call you up on the phone from the lab and ask for circuit mod ideas ....if it still fails, they just keep asking you for more ideas. I remember once recomending an "across the isol barrier" Y cap for an offline SMPS that didnt have one......the answer came back....."made it much worse!"..this was obviously a fib...when they returned, this "cross the barrier" cap had been included in the next build.
So i believe most agree that an offline SMPS for EU/UK radiated emissions testing needs to be in a metal case of some description.