Thank you for the effort!
i think its technically the best way to build up a constant current source by my own.
I found some circuits online and it might look like this in the end:
Im quite unsure how this works - also with this nasty PNP/NPN problem (i always mix up the two). Also i will have to plan it for 350mA and additionally i need a control pin to turn this on and off(do i need special transistors due to pwm?) Isn't it strange that i cant buy this in an ic?
This will make my circuit more complex than expected!
I'd like not to change the code (the tlc arduino lib is soooooo nice <3 ) - and also this part is quite expensive. 2,95€ when i take 16 which is 47,5€. Now i pay about 10€ for my tlc's and i guess if i do dc42's solution with 2 transistors i'll end up at about 20€ for the whole circuit.
Thank you both for your input!
I'd be glad if you could drop a few lines about the homemade constant current sink above!
I just read some interesting things about Constant Current Sources! In this example a voltage regulator is "abused" as ccs. The ic is an LM317 http://www.farnell.com/datasheets/76338.pdf
Here appear some BIG questionmarks! How do i turn it on or off? Simply by transistor at the end? And there is again this PNP/NPN thing...