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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?

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3 Answers 3

up vote 4 down vote accepted

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

enter image description here

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Cool, this is very helpful. All LEDs on for 100% duty cycle is definitely possible in this project, so it looks like the ULN2803A is not so overpowered after all. –  japreiss Jun 8 at 6:58

While the ULN2803 can sink 500 mA per output (with a total limit of 2.5 Amp), it will only sink what you let it - if the LEDs have resistors to limit the current to 20 mA, that's all the ULN2803 will see.

You could use individual transistors instead, but I think the convenience of a single package makes a ULN2803 a good choice.

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You can get TI 16 channel constant-current LED drivers from Digi-key for cheap and you'll only need 5.

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