On Sat, 7 Feb 2004 22:12:52 -0800, you wrote:

>I want to drive a PIC (and a 5v-only analog device) from a combination
>voltage doubler/low dropout regulator (MAX660+667, modified version of
>their appnote circuit).  The output is a small subset (5-7) of about
>30 Green/Yellow LEDs.  I was thinking of driving the LEDs directly from
>Vbatt (lower power consumption, and none of the DC/DC or regulator loss)
>but over the useful battery life of 3.2 .. 2.6v (Lithium cell or 2 AA)
>the voltage drop across the current limiting resistor varies from
>(3.2-1.9) =3D 1.3V to (2.6-1.9) =3D 0.7V.  A factor of 2.
>
>I plan to modulate the brightness with PWM, but I'd like to have the
>full 25mA (PIC pin limited) drive current available at all times.  Can
>anyone think of a way to do this?

As VBat is lower than the PIC supply, just connect the LEDs from Vbat to =
the PIC pin, and switch the
pin low to turn on.

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