Re:

>I did not want to use a Low Dropout regulator due to the loss of voltage.  I
>have not looked in a couple of years, but I think the best on the market
>still takes away 1.1 VDC.  I may go to a regulator in the future, as someone
>may want to "hotwire" the product with a 9V battery.
>I am continuing with a diode in series of the PIC's power supply.  Filter
>cap is on the PIC side of the diode.
>Best regards,


FYI, there's a design on our website in App Note AN-6 that has a
PIC12C509A running off either 3xAA (4.5V) or external 6-26Vdc. It
uses an LM2941 regulator on the unregulated DC mainly for low dropout
and reverse-hookup protection.

The kicker in getting it to work in this environment was to put a
diode in series with the output of the regulator -- this blocked the
massive (10mA) drain on the battery side of things when there was no
external input to the regulator. Also,  the battery ground is lifted
when external power is applied. With that series diode, the current
drain from the batteries in sleep mode is what you'd expect from the
PIC alone.  I have a couple of these little Fan Controllers still
running on their original batteries, which were installed in April
2001.

Another nice thing about this scheme is that the nominal voltage when
running from external supplies is very close to that of a set of new
batteries (around 4.4V).

Anyway, this may give you some ideas ...
--

  ______________________________________
   Andrew E. Kalman, Ph.D.   aek@pumpkininc.com

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