piclist 1999\10\16\071759a >
Thread: Low current power for a PIC
www.piclist.com/techref/power.htm?key=power
picon face BY : Russell McMahon email (remove spam text)



Chris,

I think a nearly perfect "plug it in and go" solution for your stated
problem (gotta cover my bases ;-)) is the Nat Semi LM2936 regulator.
This offers -

   40 volt maximum input

   15uA worst case quiescent current for 100uA load  (9uA typical)
   Rising to 200/500uA at 10mA load.
   I have found that the actual quiescent current seems to be better than
this.

   Dropout voltage is 5.5 volts

   Standard pinout.
   Std 3 pin TO92 or 8 pin SO pkg

The only real limitation of these compared to "normal" regulators is the
50mA max Iout, which probably won't be a problem in your application.
Somewhat dearer than 78L05 but may not be an issue in your application.

I use the 5 volt version but I believe a 3v version MAY be available.


Lets see, for 1 volt drop in 7 seconds on 220uF current drain is about
I = 220/E6 x 1/7 ~= 30uA.
This means you will get 1 volt of droop over 7 seconds for every 30uA of
load current.or so.
This is rough but indicative.
As you seem to have 30 volts in I guess you can droop from 30v to say 6
volts = 24 volts so load could be 30uA * 24  ~= 750uA.
Should be ample for a lowish powered PIC circuit.

Are there more details which make this not work?


regards,



     Russell McMahon
_____________________________

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