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?

When the photocell voltage output too low to power the calipers?

See the problem?