Unfortunately this doesn't look like a cheap project.
I need to drive 10 3W LEDs (for starters..), and I'm not sure how to proceed.
I've bought these 3W RGB LEDs: Amazon: 3W RGB LED
I plan on using an arduino to control a tlc5940 (unless there are better suggestions), which in turn will control these LEDs. I late plan on expanding from 10 to who knows how many, so I wanted to go ahead and use a chip that will allow me to chain them.
From what I can tell, and from what I have read, I'll use the TLC5940 to control a 2N2222 transistor (again, unless there is a better suggestion), to limit the power, thus the PWM.
The power source will be a car vehicle, so 12v-14v. As far as I'm aware I'd need something (capacitor?) to clean up any noise in the power line.
My main questions are is the 2N2222 a good transistor to use, and what else am I missing. I'm also open to any and all suggestions as to how I can make this work most efficiently/safely , as once it's installed, I don't plan on turning it off unless I upgrade it or change it.
Basically the same story as here: http://forum.arduino.cc/index.php?topic=386777.0
Bad idea to use 4-pin RGB LEDs with common anode on 12volt. ~10watt of heat per 3watt LED.
One solution is to use a buck converter to bring the LED supply (common anode) down to <=5volt.
Better to use use 6-pin RGB LEDs, three in series, for a ~10volt LED voltage.
Then you only have to bridge ~2volt. ~2watt of heat per three RGB LEDs.
Better still is three 6-pin LEDs in series, and a CC LED driver (little or no heat).
e.g. this one.
How was the 10w heat per 3w LED calculated? I looked online and didn't seem to find a good answer, or perhaps I just did not understand. Why could i not just use a resistors, or a voltage divider to bring down the 12v to 5v instead of the CC LED driver? The drivers would cost me $10~ per LED, costing 10x the cost of all LED's in total. I'm just not following why the 6-pin would be better.
I prefer not to use series for this project, as a smooth transition for the project will not be easily accomplished then, such a PWM color effects, etc.
Why could i not just use a resistors, or a voltage divider to bring down the 12v to 5v instead of the CC LED driver?
Because for a 3W LED the resistors work out to be too low to be effective at keeping a steady current as the LED heats up, so you have to have a better way of driving them.
I prefer not to use series for this project, as a smooth transition for the project will not be easily accomplished then, such a PWM color effects, etc.
As written that does not make sense. Do you mean you want individual control over each LED?
Grumpy_Mike:
As written that does not make sense. Do you mean you want individual control over each LED?
Precisely.
And in regards to the Resistors, is there a way I could just build the driver, or is it safer and easier just to buy them outright, even though it'll be costly having to buy a driver per LED?
Yes there are many ways of doing this.
The two basic ways are a constant current supply and switch mode driver. The constant current method involves burning off the excess power in a transistor or regulator. Where as the switch mode regulator, characterized by an inductor in the circuit, does not waste so much power.
houston08:
How was the 10w heat per 3w LED calculated?
A charged car battery is ~12.8volt.
Red LED for 1watt is ~2.6volt@360mA. 12.8 - 2.6 = 10.2volt has to be bridged at 360mA = 3.672watt.
Green LED for 1watt is ~3.3volt@330mA. 12.8 - 3.3 = 9.6volt has to be bridged at 330mA = 3.135watt.
Blue LED for 1watt is ~3.3volt@330mA. 12.8 - 3.3 = 9.6volt has to be bridged at 330mA = 3.135watt.
Total power loss in current limiting resistors = 9.942watt (~10watt).
Switching CC LED drivers need both LED pins per LED colour exposed, so they can't be used with 4-pin common anode LEDs. 4-pin LEDs can only be used with low voltage lineair control.
Therefore 4-pin power LEDs is usually a bad/expensive option.
With 6-pin LEDs you can wire three star bases in series.
Only ~2.8volt is lost across the current limiting resistors.
Resistive current limiting is possible (moderate heat).
6-pin LEDs also allow for switching regulators. This board can drive one, or two or three LEDs in series (one colour) from 12volt, without getting very hot.
Three of these boards, one per colour, can drive one, two, or three 6-pin star bases in series from 12volt.
They have 5volt PWM inputs.
Leo..