*gasp* Useful EDN article on tantalum caps
in [Design]
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From: Mycelium on 5 Jun 2010 14:26 On Fri, 04 Jun 2010 09:40:32 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 04 Jun 2010 09:29:31 -0700, Mycelium ><mycelium(a)thematrixattheendofthemushroomstem.org> wrote: > >>On Fri, 04 Jun 2010 10:59:32 -0500, Jim Yanik <jyanik(a)abuse.gov> wrote: >> >>> >>>TEKTRONIX used tantalums for many years in their scopes,and the failures >>>were not objectionably high. Usage was mostly on power rails,BTW. >> >> Yeah, except that they also used mostly mil spec components and >>production methodologies back then as well, and one (an engineer) could >>rely on the fact that they had been thoroughly conditioned before use on >>the production line. >> >> A hermetically sealed mil EL cap has a shelf life of decades. A COTS >>EL cap does not. There are several mechanisms that are/were in place >>during their manufacture to ensure that reliability level on those >>specialized caps, even though they differ little at the >>physical/electrical level... ie they are both paste laminated foil >>roll-ups. > >Wet-slugs don't detonate like MnO2 dry tantalums. The MIL CLR-types >are very reliable. They have silver cases, so have gotten expensive. > >I don't think these are roll-ups. They are a sintered tantalum slug >floating in a conductive paste, in a silver can. The semi-liquid paste >must put the fires out. > >John > I split off talking about ELs in the same breath. Sorry you missed it.
From: Mycelium on 5 Jun 2010 14:28 On Fri, 4 Jun 2010 10:03:13 -0700 (PDT), cassiope <fpm(a)u.washington.edu> wrote: >On Jun 4, 8:59�am, Jim Yanik <jya...(a)abuse.gov> wrote: >> Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote innews:4C091ABE.3090007(a)electrooptical.net: >> >> >> >> > On 6/4/2010 10:04 AM, John Larkin wrote: >> >> On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs >> >> <pcdhSpamMeSensel...(a)electrooptical.net> �wrote: >> >> >>> Stupid title, but actual useful info on tantalum cap behaviour: >> >> >>>http://www.edn.com/article/509092-What_a_cap_astrophe_.php >> >> >>> Now that there's this existence proof, maybe there'll be a bit >> >>> more...perhaps someone will write them another useful article, e.g. a >> >>> compendium of all two-transistor circuits. >> >> >>> Cheers >> >> >>> Phil Hobbs >> >> >> Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer >> >> and tantalum is a fuel, and only a tiny ignition source sets it off. >> >> They are fine for current-limited applications but firebombs if used >> >> to bypass power rails. Derate them 3:1 on voltage if you must use them >> >> as power bypasses. Better yet use aluminums, polymer aluminums for >> >> wide-temperature appls >> >> >> John >> >> > The interesting thing in the article is that soldering makes large tants >> > vulnerable to overvoltage failure well below their rating, and that they >> > can be reconditioned (and made much more reliable) by putting a current >> > limit on the power supply. �That's more useful for repairs or fixing >> > problems with a shipping product than for new designs, admittedly. >> > Still, I thought it was kind of cool, and remarkable for being in EDN! >> >> > Cheers >> >> > Phil Hobbs >> >> TEKTRONIX used tantalums for many years in their scopes,and the failures >> were not objectionably high. Usage was mostly on power rails,BTW. >> >> -- >> Jim Yanik > >In the late '70s Tek decreed that its design engineers should >only use tantalums with explicit series resistance (3ohms/volt IIRC), >and >enforced it with the design review process. Direct power supply >bypassing >was a no-no. This was after a lawsuit stemming from a fire started by >a Tek >product took out a large mobile lab. I think it was around that time >that Tek >also got much more serious about ensuring that connector bodies were >flame retardant, and started worrying about their switch cams with all >its >flammable delrin. > >Maybe the rate of failure was not "objectionably high", but when the >consequences >can be serious (as with the tantalum self-immolation, or with a >certain current >oil leak), you have to consider implications beyond your own immediate >product. > > -former Tek design engineer Cool first hand info and response.
From: krw on 5 Jun 2010 14:36 On Sat, 05 Jun 2010 11:22:46 -0700, Joerg <invalid(a)invalid.invalid> wrote: >krw(a)att.bizzzzzzzzzzzz wrote: >> On Sat, 05 Jun 2010 09:05:19 -0700, Joerg <invalid(a)invalid.invalid> wrote: >> >>> Michael A. Terrell wrote: >>>> George Herold wrote: >>>>> On Jun 4, 7:22 pm, John Larkin >>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>> On Fri, 4 Jun 2010 16:15:49 -0700 (PDT), Glenn Gundlach >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> <stratu...(a)yahoo.com> wrote: >>>>>>> On Jun 4, 2:10 pm, John Larkin > >[...] > >>>>>>> How do polymer caps stack up? >>>>>>> G >>>>>> Assuming that's a serious question, and not a terrible pun, they're >>>>>> great, but ESR is so low that some LDOs won't like them. >>>>> Can't you add a bit of R? >>>> >>>> L is better for tantalums. >>>> >>> Z is even better. I'd like one more hour of Z but I have to service the >>> pellet stove today ... >> >> Pellet stove? It'll be 90F today, and humid (T-boomers soon). > > >We had to heat until end of May. Global warming, you know :-) Yeah, tell me about it. I've been running the AC since the middle of April (both on this weekend). I never used to run the AC until July. ;-) >Pellet stove is done, now it's the wood stove. Way easier, piece of >cake. Then comes my all time favorite honey-do job, cleaning the ash >vacuum <cough, cough>. No ashes here; gas logs.
From: John Larkin on 5 Jun 2010 14:46 On Sat, 05 Jun 2010 11:22:46 -0700, Joerg <invalid(a)invalid.invalid> wrote: >krw(a)att.bizzzzzzzzzzzz wrote: >> On Sat, 05 Jun 2010 09:05:19 -0700, Joerg <invalid(a)invalid.invalid> wrote: >> >>> Michael A. Terrell wrote: >>>> George Herold wrote: >>>>> On Jun 4, 7:22 pm, John Larkin >>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>> On Fri, 4 Jun 2010 16:15:49 -0700 (PDT), Glenn Gundlach >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> <stratu...(a)yahoo.com> wrote: >>>>>>> On Jun 4, 2:10 pm, John Larkin > >[...] > >>>>>>> How do polymer caps stack up? >>>>>>> G >>>>>> Assuming that's a serious question, and not a terrible pun, they're >>>>>> great, but ESR is so low that some LDOs won't like them. >>>>> Can't you add a bit of R? >>>> >>>> L is better for tantalums. >>>> >>> Z is even better. I'd like one more hour of Z but I have to service the >>> pellet stove today ... >> >> Pellet stove? It'll be 90F today, and humid (T-boomers soon). > > >We had to heat until end of May. Global warming, you know :-) We have the heat on now. All year, in fact. Quite a change from New Orleans. John
From: Michael A. Terrell on 5 Jun 2010 20:26
John Larkin wrote: > > We have the heat on now. All year, in fact. Quite a change from New > Orleans. It's ironic that heating oil washes up on the beach where you don't need it. :( -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge. |