Hi all, By the way, thank you to the various group members for the responses regarding the hazardous atmosphere classifications.
One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35V....but why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. I guess what I'm looking for is some tantalum capacitor wisdom... Should we just go ahead and use 25 V or 35V caps in this 12 V application? Are tantalum caps that flaky? What is the possibility that we don't have a design problem; but just a couple of bad capacitors? Is there some piece of knowledge out there that would help us tell the difference? Chris Maxwell | Design Engineer - Optical Division email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
