I currently have a project up and running using a single TLC5940 driving 14 3.0v blue LEDs, but I plan on swapping them out for RGB leds and adding another two 5940s to drive them all; my problem now is figuring out exactly how much power it's all going to require.
All you need to know is the LED current and the number of LEDs. Where the power is actually dissipated doesn't matter (in the TLC5940? In the LEDs? It's all the same to the power supply...)
14 x RGB x 20mA is 840mA.
A 1 amp supply will run it ... but running power supplies near 100% rated load isn't good for them. Get at least double that if you're planning to leave it switched on for long periods of time (eg. 1.5 - 2 Amps).
That calculation is to make sure the chip doesn't overheat.
(Remember: The datasheet values are where the chip dies
, not values to plan for...)
but the regulated 5v from the Arduino has a 800mA limit, correct?
That's approximately where the thermal cutout will trigger, yes, but is it a good idea to run it that hot...?