Em 5/2/2010 15:56, Marc Nicholas escreveu:
> All this talk of cheap UPSes is timely...
>
> I'd like to be able to provide a few seconds of +5vdc to a device so that
> when its main power line fails it gets to "finish what its doing" (which =
it
> will if it is no longer being fed data, but needs a second or two to do s=
o).
>
> Super or ultra caps come to mind, but I've never worked with them and some
> casual Googling hasn't turned up too much of interest.
>
> Any suggestions on where to start or tips? Obviously I don't want to end =
up
> with blown caps and/or blown device!
>
> TIA.
>
> -marc
>
> P.S: Oh, power draw for the device is 150mA nominal....so hoping I can ju=
st
> do something with a Schottky, resistors and cap!
>   =

>


Start with a 200000uF capacitor charged to 6.5V, it will deliver 150mA
for about 2s before the voltage drops to 5V.
Very expensive though (over $25 only the cap).

You could use a switching regulator (buck-boost for instance) to better
use the stored energy, so you could use a smaller capacitor.
Start with a higher voltage with a less uF capacitor, and the regulator
will output a useful voltage even when the cap voltage is too low for
your circuit.

Best regards,

Isaac

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