Well Fred, here's where we get to interesting discussions...
Different folks use different core materials to achieve different goals. Knowing that in most cases a CM Choke will be faced with pulse current demands, you would think that cores would be made from materials with a large incremental current, i.e. a large current draw would result in only a small drop off in material perm. My point specifically is that CM chokes are being rated by: * wire current capability * core temp rise * anything else I've forgotten They are NOT rated for how they handle pulsed current, in fact there is no data sheet parameter that addresses this. However, as an EMC filter designer I want the best cost/performance compromise, so I need to know this. The 3 devices I've tested show dramatic differences in how they handle pulsed currents, even though they have the same rms current rating. If there are any CM Choke members on the list that would like to work on ( what I perceive to be ) this problem, please contact me directly.. It would make a good IEEE paper for the Chicago 2000 EMC Mini conference. Best regards, Derek. Fred Townsend wrote: > I've read your message twice and I still don't get your point. Saturation > is a disaster, EMI wise, (not to mention what it can do to the current in > some semiconductor devices) so as a designer you have to make sure you never > go there. If you have a 6 amp peak current then use a choke rated for 6 > amps RMS. Using any device outside it's rated parameters is cruising for a > bruising. > > Fred Townsend > DC to Light Consulting Services > > Derek Walton wrote: > > > Good day all, > > > > I'm refining the input filter of a 150 watt SMPS. Nothing flashy, just a > > few caps and a common mode choke. > > > > The current is drawn by the supply in short bursts as the DC link cap is > > charged. I've shown that peak current reaches 6 amps for up to 2 ms. > > I've also demonstrated that the CM choke, while rated for the RMS > > current ( a 2 amp device ), does saturate when the current exceeds about > > 4 amps. > > > > I've been trying to find out from the vendors, what current it takes to > > saturate the CM choke. I've had answers from CM chokes can't saturate to > > "that's not an important parameter, use the rms figure".... > > > > My question is, with over 20 potential vendors of this type of > > component, is there any way I can find out saturation performance > > without buying one of each type and testing it. I've played with 3 so > > far, the most expensive was NOT the best! I guess, I'm curious why more > > folks don't know about this effect also..... > > > > Thanks, > > > > Derek Walton > > Owner > > L. F. Research EMC Design and Test Facility > > 12790 Route 76, > > Poplar Grove, > > IL 61065. > > www.lfresearch.com > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to [email protected] > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to [email protected], > > [email protected], [email protected], or > > [email protected] (the list administrators). -- Derek Walton Owner L. F. Research EMC Design and Test Facility 12790 Route 76, Poplar Grove, IL 61065. www.lfresearch.com
