>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 02 May 2006 01:12
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Resurrecting my 78xx switcher project -- cap types?
>
>
>
>Tantalums are YEARS reliable, while electrolytics might be classed as 
>MONTHS if the temp is elevated.
>

Tantalums have some specific problems that electrolytics don't however.  They are VERY voltage sensitive, they have very little over-voltage capacity so in many applications (specificaly supply rail bypassing) they have a higher voltage rating than might be specified for an electrolytic, with the corresponding size/cost penalty.  Manufacturers design notes usualy suggest to apply no more than ~30% of the devices rated voltage in a low impedance circuit.  When tant's do fail, it's very often short circuit and given enough current capacity flames and smoke will often be generated.

Regards

Mike

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