Russell McMahon wrote:

> A BETTER WAY .................
>
> Using separate TO126 or TO220 power transistors with a modest heatsink would
> work much better.
> As normal transistors will not be able to be driven directly by a processor
> use of a darlington would be better eg


Just to be argumentative, I always use bipolar power
transistors directly driven by PIC pin, when I can.

Try BD203,  TO220 pack, (cost 50c)
= 1A, 0.2v C-E, base current 15mA.
(some TIP series are just as good and cheap)

There are good cheap low-sat bipolars around, you
just know where to look! A darlington will get hot
with 1A continuous @ about 0.9 watt, a good low sat
transistor only 0.2 watt and stome cold. :o)
-Roman

PS. Also with the BD203, I measured 19mV C-E saturation
with a 30mA load! That's almost a relay! :o)

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