On Sun, 27 Nov 2011 07:35:00 -0800 (PST),
wrote:

On Nov 26, 12:36*pm, Jeff Liebermann wrote:
On Fri, 25 Nov 2011 21:28:54 -0800 (PST),
wrote:



On Nov 25, 5:31*pm, "
wrote:
(...)
http://www.ti.com/lit/ds/symlink/tps62050.pdf
From the graph on the front page, it looks like n = ~35% *@ 15uA
output. *That's actually very good. *Thanks.

That's because of the 12uA typical quiescent current, where the chip
draws about the same current as the caliper load. *For equal currents,
that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at
2.7V in and 1.8V out (See Pg 8 Fig 4).

The chips do have a shutdown pin that cuts the quiescent current to
"less than 2uA". *Still high, but much better.

Yes, but, in the caliper context, who's going to turn the switcher
off, how, and when?

A timer. Caliper runs for 120 seconds and then shuts off. I have a
few small battery operated devices like this that have no OFF switch.
Just punch any button, and it turns on. Wait a while, and it turns
off. My Central Tools "Storm" 3C301 cheapo electronic calipers has
this feature.
http://www.amazon.com/Storm-6in-Digital-Caliper-Model/dp/B000VZ2ZB6
The unintelligible owners manual proudly highlights this feature on
the cover. Apparently, previous versions did NOT turn off
automatically. Oddly, it still has an on/off push button, even though
it will turn on if the jaws are moved.

Hmmm... the catalog says that it ships with an SR44/357 silver oxide
battery. Yet, the one I purchased had alkaline LR44 batteries.
http://www.centraltools.com/pdf/Catalog_Storm.pdf

See the problem?

Nope.

I still think that wind up power would be more interesting.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558