Rodent of Unusual Size wrote:
> Because the LEDs are in parallel

Bad idea.

> (forgot to mention that), so
> it's 300mA nominal, not 30mA.

So then where are your "strings" of LEDs?  Are those separate?

In any case 300mA is not a good excuse for a darlington (very little is).
Transistors with a minimum gain of 50 are readily available, so that means
you need 300mA/50 = 6mA base current.  The PIC can source that directly with
plenty of margin.  Even if I wanted to keep the PIC pin current low an use a
additional transistor, I still wouldn't hook it up in a darlington
configuration.  You can have a first NPN driving the second NPN, but
collector of the first NPN can go to Vdd.  Connecting it to the collector of
the second transistor would be a bad idea.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist