Lpc2000

Sorry, hadn't been following this discussion-- you might be interested 
in this very inexpensive solution: <http://www.romanblack.com/smps.htm>

David

Guillermo Prandi wrote:

> Sean, the device will be idle most of the time. The target
> application will be running ~19 days without recharging from a 12A/H
> 12V lead acid battery. Keep in mind that the battery has a self-
> discharge ratio that will leave me with ~80% of the charge (9.6 A/H).
>
> My ideal power supply should be extremely efficient in the <100 mA
> range. Due to the duty cycle (>1:60 for four days, >1:600 for 15
> days), I can stand a *linear supply* performance for currents above
> 150 mA.
>
> I'm currently experimenting with a MAX1684 for the main circuit (<150
> mA, 100 mA typical when full active) and a linear regulator (LM317)
> for the radiomodem (<5mA typical 98.3% of the time, 160~200mA average
> 1.6% of the time). I'm trying to trick the LM317 with large R1-R2
> values (~8K\ufffd) to keep power consumption low. The radiomodem will work
> well from 3.3 to 4.5V, so I can bear a considerable deal of voltage
> shift in the regulation from this side. Though this may seem a
> nonsense, I'm actually getting better numbers at the end.
>
> Guille