Chris Loiacono wrote:
>
> I have worked with AC Power control for about 15 years, and have seen all
> kinds of components fail that were spec'ed well according to datasheets.
> Smoke, charring, and ozone effects are pretty common. Often, post-mortems
> have shown that the devices' ratings mean very little when after years of
> use, contaminants of all sorts coat component surfaces, or high humidity has
> broken down a dielectric coating. They almost always do what they're
> supposed to when they're new and clean. Real-world is another story.


I've used tantalums in projects for 20+ years,
and never had one fail. I also have replaced
10+ electro caps in every TVs we repaired and
never a tantalum. I'll go tantalum anyday provided
the voltage ratings are respected. Electro caps
are little chemical time bombs full of acid and metal,
I really hate the things, especially in Australia
where we get erratic mains voltages and high
temperatures. If I have to use electros in
something sensitive I use the 105'C electros
and overrate voltage at about 3x and mount them
away from heatsinks and big resistors. Some TV
makers deliberately put small electros next to
large heatsinks. Bastards, they're not stupid. :o)

One good trick with any PSU cap is to put a
resistor in series between the retifier bridge
and the cap. This reduces startup surge current
and increases the diode conduction time, both good
things. Most of the commercial manufacturers use
resistors anywhere sensitive, mainly because they
can then use cheap weak parts and still get away
with it. But if you use the safety resistors and
GOOD parts you get a product that runs for 20
years. :o)
-Roman

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