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Old 05-16-2010, 03:25 PM   #3401 (permalink)
Tesseract
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Join Date: Feb 2009
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Quote:
Originally Posted by bigh View Post
Hi Tesseract, sorry It wasn't my intention to reverse engineer the Soliton1. I was intruiged as to "Cutting edge capacitor: Special purpose high reliability/low loss 600V film capacitor. No electrolytic capacitors are used in power stage. "
No problem. I'm not all bent out of shape or in anguish or anything, I just wanted to let you folks know that we can all get along. If nothing else we serve entirely different markets


Quote:
Originally Posted by bigh View Post
...I'm looking to learn what my options are and select what the best option for my purposes is. Ie high voltage long lasting, and easy to hook up. The fact that your controller used no electrolytic caps is very interesting, as I found the rated lifespan of the electrolytics to be very poor.
Yes, film capacitors are superior to electrolytics in all aspects EXCEPT one: capacitance per unit volume. If you need lots of capacitance you want to use an electrolytic; if you need lots of anything else you pretty much are better off with film. Specifically, polyester or polypropylene. Mixed films are good too.

You don't really need a high dV/dt rating for this application - i.e., pulse rated capacitors aren't so important - but you do want low ESL, ESR and Rth. The latter is very important because of IČR heating (the ripple current through the ESR).

You can use many PC board mounted capacitors in parallel or you can use screw mount or stud mount caps attached to a bus structure or bus bars. Lots of ways to go with this.

There are even film caps that are direct replacements for electrolytics, with higher ripple current vs. lower capacitance.

BTW - the rule of thumb for sizing electrolytics based on ripple current is 20mA/uF max. Secondly, give them at least a 50% voltage margin when used in hard-switched converter circuits. Thirdly, every 10-11C drop in internal temperature doubles the life of the capacitor.

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