Edson Brusque wrote...

>    Yes, I'm trying to make this circuit to work but I don't have the =
right
>inductors. The cheap inductors doesn't work very well and I only have
>"professional" (:^) inductors of 100uH.
>
>    By target is a circuit to obtain 5V @ 100-150mA from two alkaline (2=
 x
>1.5V) or 2 NiMH (2 x 1.2V) cells. I'm trying with the LT1173-5 and =
various
>inductors/caps/resistors, but can't suck more than 80mA when the input =
drops
>bellow 2.5V. :(
>
>    Sugestions? Maybe another thread...

The diagram labeled "3V to 5V Step-Up Converter" on page 13 of the
LT1173 data sheet should do more or less what you want, although the
current you're asking it to deliver is right at the very upper end of
its capabilities with a 3V input and well beyond what it's capable of
doing with a 2.4 volt input.

Generally, with these IC switching regulators you have to stick pretty
close to the components recommended by the IC manufacturer (see Table 1
in the LT1173 data sheet), especially when you're trying to drag the
maximum possible performance out of the part.  Experimenting with the
circuit component values is unlikely to net you much.

If I were in your situation, I think I'd look around among the various
offerings by Linear Tech, Maxim, and National Semiconductor to try and
find a switcher with a little more "beef".  A good candidate would be a
part that's capable of delivering at least 50% more current than what
you need; when your requirements fall well within a part's capabilities,
design becomes a whole lot easier and more tolerant of component
substitutions.

Hope this helps...

Dave

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