On Feb 5, 2010, at 10:48 AM, Isaac Marino Bavaresco wrote:

> Very expensive though (over $25 only the cap).

Um.  You're looking at different caps than I would.

You need to know how much current your device will need, and what the  
minimum voltage it can use.  Isaac's capacitor is particularly  
expensive because he wanted a starting voltage of 6.5V and a current  
capability of 150mA, which moves it out of the realm of most  
"supercaps."  (You can get a .47F supercap with high current  
capability for about $4, but it's only 5.5V.  Or you can get a .1F  
6.3V double layer cap for about $6, but it's not spec'ed for high  
current. (hmm.  30mohm.  MIGHT work...)  Or 3x 1.5F 2.5V caps (0.5F @  
7.5V in series) for about $3 each.)

The "usual" setup seems to be to just connect the cap across the  
supply rails of of memory/microprocessor chips that are designed to  
have some level of operation down to voltages significantly lower than  
their normal supply voltage...  Adding more capacitors for higher  
voltage seems to be about the same price as adding a boost converter  
style UPS circuit...

BillW

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