Question on small capacitors...

Tantalums are very good electrolytic caps with one weakness. If you drive then up to full voltage too quickly, they sometimes catch fire. Other than that, they are fine.

Which they love to do. Very inconvenient.

They generally won't catch fire if they explode first.

Best regards, Spehro Pefhany

Huh. Thank you for the warnings. Further question: what if the 1uF tantalum cap is rated at 35V, and being driven at only 9V? Would that make them any safer?

Do appreciate the help.

Dave

By quite a bit.

Thank you, John. I am still fairly new at all of this, and there is obviously a lot I don't know...

Dave

Ratios like 3:1 seem to be pretty good. But tantalums are so erratic that it's hard to draw hard conclusions.

A recent LTC datasheet claims that "tantalums don't explode when used across the outputs of regulators" which I know to be nonsense... they certainly do explode across the outputs of LM1117's, even derated 2:1. The same LTC datasheet, as I recall, alludes to some other upcoming appnote about tantalums.

Polymer tantalums are apparently better than the classic MnO2 detonators.

John

There's a lot we all don't know. As you gain experience in electronic design, you begin to not know at a much higher level.

Like Woody Allen said, "now that I'm famous, I'm strinking out with a much better class of women."

John

For what it's worth, I've never had a problem with tantalums. As far as operationally, 1 uF is 1 uF. And polarized is polarized. :-)

Personally, I suspect that the people who blow up tantalums did it because they'd installed them backwards, then blame the tantalum so they don't get caught being clumsy. ;-)

IOW, go for it.

Cheers! Rich

What in the _world_ do you guys do to your capacitors? In 40 years, (or however long there have been tantalum caps), I've _never_ seen one explode or burn.

I think you guys are installing them backwards, and are too embarrassed to admit it. ;-)

Cheers! Rich

Boy, I wish I had your touch! One summer was spent repairing a bunch of circuit boards where most of the failures were tantalum caps on the power supplies. Of course, they were operating just below their rated voltage. Ahh, fond memories of college years. Now days, I'm finding bulging Al electrolytics leaking their guts in consumer products. Icky!!

A bipolar bicycle maybe the answer, you can normally only pedal in one direction

martin

LOL! Thank you. I like that.

Yes, very few of us know very much. Seems like the more I learn, the more I find out I don't know...

Dave

Hmmm. Thank you for the input. Maybe I'll just stay away from tantalums in general...

Dave

No, but the drop ceiling will. (Don't ask...)

-mpm

If you do that, you have learned more than there was to know. Tantalums are more stable and have low and stable leakage current, so they are well suited for timing applications, like yours. The resistors that produce the RC time constant also protect the capacitor from any sudden high charge current. Your application is right down the middle of the sweet spot for tantalum electrolytics.

Oh. Okay. Thank you. Well, maybe I actually did learn something.

Dave

Of course, the cure is a bicycle made with "space age alloys", you know, the aluminum-lithium alloys.

Tim

-- Deep Fryer: A very philosophical monk. Website @

Years ago we had many problems with tantalums burning (sometimes supersonically ;). The resulting flame from these particular caps was directed down into the board, which burned and often caused a small interplane short. Because there was a thousand or so amps behind the planes they got hot, shorting further, until the whole shebang melted down. The resulting smoke and fire upset the customer who just paid a couple of megabux for the system. The customer then upset our execs, who...

Easy to do, but that's not the only way to get fire. There is a difference between manufacturers too. Some are far better than others. The great capacitor caper was another issue.