EMI choke before switching power supply

I don't see any problem with that, but I would be doubtful whether it has much of an effect on a SMPS. They themselves create a lot of EMI and the emissions from the PS itself would probably reduce the effect that the choke has on the output. If you are putting it in to prevent the SMPS from injecting noise onto the mains, I wouldn't be too sure whether the choke would have the desired effect either.
 
Its a common mode choke, where that 27mh inductance is not unusual for a small 1a rated choke. Way to improve its common mode efficacy is by following it with Y2 caps to ground. While a measurable improvement, adding more crap to the ground is IMO, rarely a positive. The CMC will also have substantial leakage inductance (100-500uH), useful for filtering normal/differential mode noise. Its well worth the effort to flank the CMC with X2 caps (typically .47uf) and bypass X2 caps, if you see fit (which I do). This will further attenuate normal/differential noise both to and fro.
 
Also be aware that adding Y caps increases what is called "leakage current" from the AC mains into the safety earth connection. Should this connection ever fail, the effect of leakage current is to raise the chassis to a voltage which now has the potential of becoming leathal.

Y caps are also "special" in that they need to be approved specifically for this use. Y caps are constructed such that their failure mode is always to go open and never to short.

Unless you really have a good reason to play with additional EMI filtering it might be better to assume the designers of the power supply did their job and no additional filtering is needed.

Cheers,
Kevin
 
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Unless you really have a good reason to play with additional EMI filtering it might be better to assume the designers of the power supply did their job and no additional filtering is needed.

Cheers,
Kevin

An assumption that I've never found to be true. Such switching supplies are efforts whose only objective is comply with FCC regs (leastwise here in the States), which to a minor extent addresses crap going out, but never in.

NuForce amps, the poster child of a switching supply switching amp as high end, is unlistenable without proper power conditioning. I've yet to encounter a DVD or CD player under $10,000 that doesn't substantially benefit from appropriate series inductive, parallel capacitive conditioning.

But trying to build anything based upon a found component of unknown (detailed) characteristics, is a waste of everyone's time, including the finders. Use something appropriate for the task(s) where you actually know what you've got.
 
I've yet to encounter a DVD or CD player under $10,000 that doesn't substantially benefit from appropriate series inductive, parallel capacitive conditioning.

But trying to build anything based upon a found component of unknown (detailed) characteristics, is a waste of everyone's time...

Is that based on series of double blind tests? If not, please don't waste everyone's time... ;)

Tim
 

erachiel

Member
2010-10-18 2:50 pm
First of all thanks for all the answers.
I found the b
Filter%20with%20X2%20and%20Y2.jpg
est possible s
Filter%20with%20X2%20and%20Y2.jpg
olution (for me).
 

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Is that based on series of double blind tests? If not, please don't waste everyone's time... ;)

Tim

There is a reason the good Lord, in her infinite wisdom has given us switches, you might try them some time. :eek: I use 2 4pdt. (with ss power amps as the load, you can use a single 4pdt CO switch) While this does not give us a double blind computerized protocol, it does provide a very good and straightforward single blind evaluation, with the same number of toggle switch 'clacks' and less than a 2 seconds between samples.

I like my spectrum analyzer as well as the next dweeb, maybe more so. But when all is said and done, sometimes its informative to just listen, in as a controlled a manner as feasibly possible. ;)

FWIW
 
Sorry, knowing which side of the switch is "I did something to this" invalidates the test. :)

No need to apologize at all. While having someone else throwing the switches out of my view may not satisfy your criteria, it does mine, and results in a better project. I leave the peer reviewed journal articles to my mathematician son. If subjective optimization doesn't compromise measurable characteristics, I really can't see why you'd be concerned.
 
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