I want to drive around 80 LEDs from an Arduino with 10 8-bit shift registers. (Some will be RGB LEDs; I count those as 3.) I know of the TPIC6B595 high power shift register but it's expensive: 1.75 USD from DigiKey and Mouser. I would prefer to do this cheaper.
I can get 74HC595 low power shift registers for 50 cents and ULN2803A Darlington arrays for 65 cents from Futurlec. That is a total of 1.15, so I'd save $6 on the whole setup.
But the ULN2803A is way overpowered for LED's – each pin can sink 500 mA! Is there anything similar to the ULN2803A, but lower power and even cheaper?
Best Answer
ULN2003A are usually quite a bit cheaper, but only 7 channels.
BTW, they're not really good for 500mA, if you read the datasheet critically, you'll see it's more like 50 or 60mA per channel with all channels active, assuming a reasonable temperature range.
From the Toshiba datasheet, the lower graph is for Ta = 85°C