A couple of ideas:
1. Use a  pre-regulator to a low drop out regulator to get the Vin low
enough.
2. Use LP mode xtal oscillator to lower operating current.






Chris Eddy <ceddy@NB.NET>@MITVMA.MIT.EDU> on 10/15/1999 09:30:18 AM

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Subject:  Low current power for a PIC


Associates;

I have a PIC that must live off of a 220uF cap for 7 seconds.  I can get
the PIC to consume low power, but I am having trouble getting the
regulator designed.  The 78L05 sucks 2-3mA Q current, way too much.
Looking for 50-100uA.  The low dropout regs are neat, but they have a
very limitted Vin max.  I need 30V.  I built a pass regulator with a
res, zener, and NPN trans, which meets my goals, but since the current
through the zener is low, then as the V on the C drops off, then the V
on the zener drops off, and the V on the PIC droops as well.  This
causes the RC osc to skew, and my highly important timer gives me
predictable garbage!

Any great ideas?

Chris Eddy
Pioneer Microsystems, Inc.