Author Topic: Offline OffTheShelf SMPS wont pass radiated EMC?  (Read 1091 times)

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Offline Faringdon

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Offline OffTheShelf SMPS wont pass radiated EMC?
« on: June 14, 2021, 08:32:54 pm »
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.html

Also, its datasheet  doesnt assure that it turns off below 85VAC...do you know if it does?
 

Offline Gyro

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #1 on: June 14, 2021, 09:22:07 pm »
It's a basic PCB mount psu module treez, 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?


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« Last Edit: June 14, 2021, 09:31:01 pm by Gyro »
Regards, Chris

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Offline Faringdon

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #2 on: June 15, 2021, 04:19:21 am »
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?
 

Offline Gyro

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #3 on: June 15, 2021, 08:44:47 am »
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 input and output 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.
« Last Edit: June 15, 2021, 08:46:32 am by Gyro »
Regards, Chris

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Offline mikeselectricstuff

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #4 on: June 15, 2021, 09:25:22 am »
Also bear in mind that some PSUs which pass EMC are only tested with a resistive load, and can fail under certain load conditions
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Offline jc101

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #5 on: June 15, 2021, 06:46:39 pm »
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?
 
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Offline Faringdon

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #6 on: July 30, 2021, 09:32:34 pm »
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/

Quote
A prime reason for using an Earthed metal enclosure is that we want to prevent radiation from inside the equipment from spilling out. Without a metal enclosure, whether Earthed or not, there is little chance that an off-line switching power supply can ever comply with the radiated emission limits.

Would you agree with this?
« Last Edit: July 31, 2021, 06:48:23 am by Faringdon »
 

Offline Gyro

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Re: Offline OffTheShelf SMPS wont pass radiated EMC?
« Reply #7 on: July 31, 2021, 09:59:18 am »
https://www.eevblog.com/forum/renewable-energy/earthing-the-secondary-of-an-offline-isolated-smps/msg3618046/#msg3618046


P.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?  ::)
« Last Edit: July 31, 2021, 11:22:29 am by Gyro »
Regards, Chris

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