T
treez
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The following article (on page 4) from mag-inc.com gives a design example for a common mode choke for an offline SMPS. It specifies that the common mode choke will have an impedance of 1000 ohms at 10khz.
Why does it bother to specify impedance at such low frequency? Common mode noise is noise that is typically above several MHz…because it needs to be that high in frequency to allow it to couple out through stray capacitances etc.
“Common Mode inductors for EMI filters require careful attention to core material selection.”
www.mag-inc.com/File Library/Product Literature/Ferrite Literature/fc-s5.pdf
Common mode noise is noise that has come in to the offline SMPS through the live line, then gone in to the SMPS, but instead of coming back out through the neutral, it couples out of the power supply and flows back to earth ground. -As you can tell, signals at 10khz simply cannot do this, at least not with significant amplitude....so why is their example at 10khz?
Related thread:
https://www.edaboard.com/threads/231845/
Why does it bother to specify impedance at such low frequency? Common mode noise is noise that is typically above several MHz…because it needs to be that high in frequency to allow it to couple out through stray capacitances etc.
“Common Mode inductors for EMI filters require careful attention to core material selection.”
www.mag-inc.com/File Library/Product Literature/Ferrite Literature/fc-s5.pdf
Common mode noise is noise that has come in to the offline SMPS through the live line, then gone in to the SMPS, but instead of coming back out through the neutral, it couples out of the power supply and flows back to earth ground. -As you can tell, signals at 10khz simply cannot do this, at least not with significant amplitude....so why is their example at 10khz?
Related thread:
https://www.edaboard.com/threads/231845/
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