It seems when anyone offers a suggestion on here that cost more than free the
suggestion has to be given the bad mouth. If $.59 for a ULN2803 or $.39 for a
ULN2003 is too much for costs, then visit the local junk dealer, he may have a
bargain on used FETS. Yes they are a darlington driver, yes they have a high
voltage drop. If you want high current drivers then buy power FETS.

Vern

William Chops Westfield wrote:

>     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
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads