22 Sep
2014
22 Sep
'14
3:25 p.m.
On Mon, 22 Sep 2014, drlegendre . wrote:
On Mon, Sep 22, 2014 at 5:50 AM, Chris Pye <pye at
mactec.com.au> wrote:
I've been replacing tantalums in some older equipment with modern
electrolytics (low ESR, high ripple rated). Nichicon HE, Nichicon PW, and
Rubycon ZLH seem to work fine as replacements for tantalums that were used
as bypass or other general purpose caps. I think at one point designers
were needlessly using more tantalums because they seemed different, or
thought of them as an "improved" replacement for aluminum electrolytics.
I have some RF gear (wireless networking gear, pre-wifi) that happens to
unfortunately be filled with 100s of SMD tantalums. Right now none of it
is functional /because/ a whole bunch of them have shorted out and burned
up. Replacing those worries me because I have no schematics for the boards
and using modern parts could possibly upset the RF portions of the
devices. Because they are SMD parts, my only two real options are to
either use tantalums again (which may be fine since newer parts seem to be
more reliable, but using them will be /very/ expensive), or using a modern
SMD polymer-aluminum capacitors such as a Panasonic's SP-Cap.
Tantalum capacitors are a type of electrolytic,
and are usually
polarised (I?ve never seen one that isn?t).
They usually burn up pretty quickly if they are the wrong way around.
Hey, I just had a bad idea.
I suppose a non-polar tantalum could be built the same way as a
non-polar aluminium electrolytic.. two caps in series, in one package,
with the negative leads tied together. ;-)
But what a horrible thought - just having one of those obnoxious little
bombs in one location is bad enough. If your circuit won't perform
without one, maybe you should just re-design the circuit or something...