> 10 LEDs apiece, superbright white, 3.5VDC/30mA apiece.
> This is a ground-up project, so I'm going to build the
> power supply as well.  I intend to drive the LEDs
> through Darlingtons driven in turn by the PIC's outputs.

This here is very close to what you're doing

http://www.piclist.com/techref/microchip/HV_PWM_Proto.htm

I'd be quite happy to go through the method with you

There are many step-up switchmode controllers available - even the
PIC itself. That means you don't have to stick with low-voltage DC,
eg typical wall-wart supplies, and can change from parallel to series
LEDs

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