Switcher EMC design

[marce]

Some interesting articles regarding EMC and switch mode design which may be of interest to any one designing and laying out any form switching circuit be it an SMPS or Class D amp. As these circuits can be one of the main causes of noise in circuits following good EMC and layout guidelines is critical.
Anyway hope they are of interest and if anyone has any additions I would be grateful.

Excellent articles on EMC issues of SMPS design near the back.
http://www.compliance-club.com/pdf/Issue93.pdf
http://www.compliance-club.com/pdf/Issue94.pdf
http://www.nxp.com/documents/application_note/AN10912.pdf
http://www.onsemi.com/pub_link/Collateral/AND8301-D.PDF

An eclectic mix of app notes from my collection.
http://focus.ti.com/lit/ml/slup227/slup227.pdf
http://focus.ti.com/lit/sg/sluw001d/sluw001d.pdf
http://www.national.com/an/AN/AN-1149.pdf
http://www.national.com/an/AN/AN-1229.pdf
http://www.national.com/an/AN/AN-1791.pdf
http://www.fairchildsemi.com/an/AN/AN-6203.pdf
http://www.fairchildsemi.com/an/AN/AN-6858.pdf
http://www.fairchildsemi.com/an/AN/AN-42036.pdf
http://www.johansondielectrics.com/...otes/application/JDI_DC-DC-Trends_2006-03.pdf
http://fplreflib.findlay.co.uk/articles/18508\LA6942.pdf
http://www.national.com/assets/en/appnotes/f4.pdf
http://www.compliance-club.com/pdf/Issue93.pdf
http://www.compliance-club.com/pdf/Issue94.pdf

http://www.nxp.com/documents/application_note/AN10912.pdf
http://www.onsemi.com/pub_link/Collateral/AND8301-D.PDF

 

[kubarebo]

I have two hard rules for EMC:

1. know your parasitics
2. keep those loops small

 

[marce]

Ahh if life was that simple
I probably wouldn't need Henry Otts publications amongst other things.
EMC and signal integrity, considering the effect they can have on sound quality, dont seem to be of much interest?
Anyway part three of EMC journal articles, "Design Techniques for HF isolating Transformers" is out. Page 35:
http://www.compliance-club.com/pdf/Issue95.pdf

Have fun

 

[DF96]

Don't build switching circuits unless you really understand RF? A simple rule like that might reduce the electronic smog we all suffer from nowadays.

 

[marce]

Lots of people on this site build there own SMPS's, and modulated SMPS's (class D) these articles are for their information, as how many of them have their designs and layouts EMC tested. How many of them understand high frequency design, one wonders, or the implications of EMC, or how much noise these things can generate.
I personaly I like doing SMPS layout, I find it fun, and a break from the monotany of digital layout, the large DI/Dt adds a bit of spice to life
As to the elctonic smog, PLT (power line communications) is only going to make things worse, but BT have had an excemtion from ofcom as the basis of PLT is adding EMI to the 50Hz powerlines.
The other thing that prompted me to post this information, is the fact that I have seen comments on threads for switching circuits, wher views such as EMC dosn't matter as it is a diy design!!!

 

[DF96]

I personaly I like doing SMPS layout, I find it fun, and a break from the monotany of digital layout, the large DI/Dt adds a bit of spice to life

Yes, you have the advantage of knowing what you are doing. This will also mean that you know when you are nearing the limits of your understanding so need to be more cautious. Some people don't have this advantage - they merely blunder on.

Actually, the odd DIYer getting it wrong will probably have less effect (unless he has a radio amateur or SWL next door) than the widespread EMC abuse perpetrated by people who should know better.

 

[marce]

I live next door to someone who changed their network from wireless to powerline based netwrok a few months ago, I used to have a wirless TV transmitter for watching SKY in bed. When they changed I ended up watching their data insted.
What worries me with EMC and DIY is that people go to the limits to improve the sound, and yet EMC or lack of EMC awareness is probably causing them problems. The problem is though is having the equipement to test for EMC. Maybe a DIY EMC testing thread, to investigate how some basic testing could be done with basic equipement.

 

[elevator]

Maybe a DIY EMC testing thread, to investigate how some basic testing could be done with basic equipement.

Sure, and I might add my faithful AM/SW transistor radio to that equipment

 

[magnoman]

Marce,

Thanks for posting all those links (just skimmed through them quickly).
It's been many years since I've done a SMPS design (120KHz and that was relatively fast then) but at least in those days a simple 50MHz current probe really did reveal a lot about the design. Both time and frequency domain measurements of especially the input and output common mode currents to some metallic plane gave me a very stable technique to measure differences when evaluating differences in design or implementation (same with differential current but that was always easier to measure and specify).
Of course one needs some goal for these measurements, in my case the sensors powered from the SMPS ultimately gave the me the "the noise limit is no longer the SMPS" which turned out to be 2mA common mode current in my configuration and test set. This very simplified and approximate technique held up for many years (and the final complete sensor units would then be EMC tested).

Thanks again
-Antonio

 

[marce]

Rather late and tardy, but here is an update on the series of articles by Keith Armstrong, sorry.

An update on the Keith Armstrong articles on EMC and power converters...

http://www.compliance-club.com/pdf/issue95.pdf
EMC design of high-frequency power “switchers” and “choppers” Design techniques for HF isolating transformers

http://www.compliance-club.com/pdf/issue96.pdf
EMC design of high-frequency power “switchers” and “choppers” Design techniques for LF (mains) rectifiers

http://www.compliance-club.com/pdf/issue97.pdf

EMC design of high-frequency power “switchers” and “choppers” Design techniques for high frequency (HF) output rectifiers