On Nov 25, 5:31*pm, "
wrote:
On Fri, 25 Nov 2011 07:06:57 -0800 (PST), wrote:
On Nov 25, 12:46*am, Jeff Liebermann wrote:
On Thu, 24 Nov 2011 18:13:15 -0800 (PST),
wrote:

I found this, which calculates and measures caliper battery life:
http://www.davehylands.com/Machinist/Caliper-Batteries/

Yes, good site. *I linked to it earlier in this thread.

Small, cheap and simple are the main factors here. *The r.c.m. guys
aren't going to be building switching regulators, and switching
regulators generally aren't more efficient at these power levels
anyhow--their quiescent current draw's too high.

True. *However, switching regulators usually have some manner of load
shedding when the supply voltage is insufficient. *Below that
threshold, the current drain is usually in nanoamps.

(I've made a study of designing microwatt switchers, from scratch.
It's possible, but wholly inappropriate here.)

You're ahead of me. *I've never designed anything in that low power
class. *Different world. *Can you point me to a suitable (or close to
suitable) regulator chip?

There aren't any ICs with low enough Iq, at least not that I know of.
I used discrete transistors.

There are some pretty good ones, designed for USB applications, but I don't
thing they're quite good enough for this. The TPS6205x Iq is around 5uA to and
in shutdown less than 2uA. *You're looking for something an order of magnitude
better than this?

...

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.

My designs were mostly boost topology, so there may be ICs I didn't
consider (plus new ICs I haven't seen). I did some nutty stuff, like
nano-amp oscillators and micro-amp switchers that were roughly 75%
efficient.

--
Cheers,
James Arthur