It CAN do 500mA but poorly. I believe about 1.7v Vce
    saturation, pretty sad really since you can get 8x
    BC337 transistor and 8x base resistor for a fraction
    of the price and MUCH MUCH better performance.

Well, it IS a darlington driver, so it has the usual darlington Vce (poor.)
On the other hand, ULN2003's are pretty cheap; I was going to suggest one
of the 74 series "bus driver" chips (74x240, etc), except I discovered:

1) The 74x driver chips tend to be more expensive than a ULN2003 $.86 vs
   $.58 from digikey. or something like that.  In ones.)
2) The bus driver chips I was thinking of didn't drive as much current as
   I thought they did. :-(  Unless TI's datasheets got screwed up on their
   website.  I could SWEAR that the "buffer/driver" chips had significant
   output drive capability for all families, but I see that a 74hc240 only
   does +/-6mA (compared to +/-4mA for 74hc00.))

The excess voltage drop won't hurt an 5V LED driver, except maybe if you're
driving UV Leds.  You either eat the power in the driver chip, or in your
current limitting resistor; shouldn't matter much which.

The ULN parts have built-in protection diodes as well.  I've got this lovely
relay driver PCB I designed, with transistors and base resistors and diodes
and such, and I'm agonizing over why I shouldn't just rip most of that out
and stick in a ULN chip...  Sigh.

BillW

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