Re: Help with power issues

On Mar 31, 10:13 pm, "m...@xxxxxxxxx" <m...@xxxxxxxxx> wrote:
On Mar 31, 9:53 pm, linnix <m...@xxxxxxxxxxxxxxxxxx> wrote:



On Mar 31, 9:44 pm, "m...@xxxxxxxxx" <m...@xxxxxxxxx> wrote:

On Mar 31, 1:21 pm, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:

James Arthur wrote:
linnix wrote:
On Mar 31, 10:58 am, linnix <m...@xxxxxxxxxxxxxxxxxx> wrote:
On Mar 31, 10:33 am, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:

< snip>

Suggest using micropower voltage regulators. Zeners are horrible.

Yes, but standby power is less than 100µA, with everything else off
except the µC. Active power is only for several minutes once in
several days or weeks. Standby power needs to be several months on
two CR2032.

Here is the simplified schematic:

http://linnix.com/SigmaDeltaEpilson.gif

Actually, we have considered a custom made 4V LDO with 3.5µA standby
current. But we are trying to avoid the $3000 minimum order for the
moment, until necessary, we will just stuff it with zeners or even 6
regular diodes.

Seiko Instruments has a number of uA-quiescent regulators.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=728-...

data***:http://data***.sii-ic.com/en/voltage_regulator/S812C_E.pdf

About $0.30 @ qty 3,000, as you said.

That looks just the job.

Graham

The LDOs I've designed, as well as most of the industry these days,
has reverse polarity protection. This DIY design doesn't, and his
budget (voltage or dollars) can't tolerate a series diode.

Of course, I speak from a vacuum since I never had to design anything
for sale other than chips, so perhaps crappy engineering is the way of
the world.

If you never have to deal with the budget, then you never have to deal
with difficult issues. I know LDO is the solution from the beginning,
but they are not cheap. We gave them a single chip perfect solution
(Atmega169) with nothing else. Of course, they are coming back with
sticker shock when they put it in production.

Oh, I deal with budgets, but with a chip, you sell value. You just
build the LDO in the chip because the customer needs it. In addition
to the cost of silicon, you need to worry about the cost of external
components, so you may spec your design for crappier external
components than you would like.

This reminds me of the early Chinese LED lights done with coin cells
to avoid an expensive DC/DC. The Chinese sold junk, everyone else sold
managed power, and eventually the Chinese came around. AA or AAA cells
are cheaper than coin cells. In fact, I avoid products with coin cells
and often won't buy a product with AAA cells if there is an AA
solution on the market, even at a higher cost. Again, it's the cost of
ownership.

Changing battery type is out of the question. CR2032s are less than
0.10 each wholesale. They are only expensive in retail, due to
distribution costs. The ASIC can standby with less than 10µA, so a
10K resistor from the coil cell directly with keep it in standby for
months, after switching everything off. LDO is just a kludge, it is
not necessary for the final version. The real fix is clamping the LCD
driver outputs.
.

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