there will be at least 15 i.e. 15x150mA= ~2.5Anot controlling brightness..
here is oval led..
https://img.diytrade.com/cdimg/974467/9957134/0/1249291141/5_2_x_3_8mm_Oval_LED_Lamp_Series.jpg
https://www.google.co.in/search?q=oval led&client=firefox-a&hs=pkw&rls=org.mozilla:en-USfficial&channel=np&source=lnms&tbm=isch&sa=X&ei=zinGUpObM46qrAeatIHQBA&ved=0CAkQ_AUoAQ&biw=1376&bih=651#channel=np&q=oval led board&rls=org.mozilla:en-US fficial&tbm=isch
Hi again,
Ok so you've got to handle 2.5 amps now we know the full current load, which says a lot about this project.
If i sounded like i was a little against using a Darlington for this project before then let me update that to state that now i can see that it is definitely time for the Darlington to go. That particular device can drop as much as 4 volts and at 2.5 amps that means we'd have to get rid of 10 watts of heating power! That is far too much for such a simple project like this in this day and age. If you listen closely, you'll hear the cries of a MOSFET coming into play here <chuckle>.
You can a get high current logic level MOSFET that would handle this on/off chore in a heartbeat with very little power loss. Of course that shifts the burden of current limit to the current limiting resistor(s), but that's really where we want it anyway. That way we can use a separate resistor for each LED string and that means less power per resistor too. And the logic level MOSFET (N channel) means we can drive it with the uC pin or with a cheap tiny two transistor driver and get good results with a frequency that isnt too high (if we also want to use PWM). It's easier to go with low frequency anyway when using a uC for PWM.
So the best solution is probably to use an N channel MOSFET logic level transistor and try driving it from the uC pin itself and dont go over about maybe 5kHz if you decide to PWM it. Use separate resistors for each LED string and i think you will find this to work exceptionally well. Choose a nice high current MOSFET for low dissipation there. If the MOSFET gets hot driving from the uC pin alone then use a two transistor driver (two small transistors, schematic to follow).
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