Offline OffTheShelf SMPS wont pass radiated EMC? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: June 14, 2021, 08:32:54 pm
content: Hi,Would you agree, the 12Vout, 15W version of this Mornsun LS15 series SMPS woudlnt be expected to pass radiated emissions EMC test, unless it was housed in a metal screened enclosure?https://www.mornsun-power.com/html/pdf/LS15-13B12SS.htmlAlso, its datasheet doesnt assure that it turns off below 85VAC...do you know if it does?

author: Gyro
author_rank: Super Contributor
timestamp: June 14, 2021, 09:22:07 pm
content: It's a basic PCB mount psu moduletreez, it's designed to be built into a product.The pcb doesn't contain any EMC suppression components, you're supposed to use the additional suppression and protective components as indicated on pages 3 and 4 of the datasheet.Would you agree?https://www.eevblog.com/forum/profile/?area=showposts;u=776359

author: Faringdon
author_rank: Super Contributor
timestamp: June 15, 2021, 04:19:21 am
content: Thanks yes, i agree with that.Also, i believe that to pass radiated emissions, it will need to be mounted in a metal shielded box, would you concur with this?

author: Gyro
author_rank: Super Contributor
timestamp: June 15, 2021, 08:44:47 am
content: No, I wouldn't concur with this, treez.There are many SMPSs of this power level range that pass radiated emissions without a metal case, many power bricks for a start, some use no screening, some use selective insulated copper foil screening in a plastic case.There are many variables - the quality of your main PCB layout, routing, and suppression components, Y caps placement etc., whether you are using a 3 wire mains lead (whether the metal shielded box would be low impedance earthed or not), radiated emissions from inputandoutput leads etc. It is down to how well you integrate this oem module into your product and characterise it.I remember this being explained to you several times under your various identities.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 15, 2021, 09:25:22 am
content: Also bear in mind that some PSUs which pass EMC are only tested with a resistive load, and can fail under certain load conditions

author: jc101
author_rank: Frequent Contributor
timestamp: June 15, 2021, 06:46:39 pm
content: The datasheet provides example EMC filtering in the datasheet, and what design is expected to pass what standard. Why not get one, add the recommended filtering and have a probe around and see what is thrown out?

author: Faringdon
author_rank: Super Contributor
timestamp: July 30, 2021, 09:32:34 pm
content: Thanks, the following document confirms that an hard switched offline SMPS cannot pass radiated emissions EMC testing without being in an earthed enclosure....https://www.edn.com/safety-concerns-for-practical-emi-line-filters/QuoteWould you agree with this?

author: Gyro
author_rank: Super Contributor
timestamp: July 31, 2021, 09:59:18 am
content: https://www.eevblog.com/forum/renewable-energy/earthing-the-secondary-of-an-offline-isolated-smps/msg3618046/#msg3618046P.S. That EDN article appears very naively written, it makes absolutely no reference to Class-I vs Class-II construction, hence all of the references to earthed metalwork (Class-I) its clearances are out of date and you will (should have) noticed that it was written way back in 2003.Would you agree?