Hi,
Can you help me, I want to control very bright RGB LED. It's not programming question I just asking about voltage and mah.
As you see, it needs 12V output and 350mAh for each led. How to realise this? Which Arduino/tools enough power?
Hi,
Can you help me, I want to control very bright RGB LED. It's not programming question I just asking about voltage and mah.
As you see, it needs 12V output and 350mAh for each led. How to realise this? Which Arduino/tools enough power?
It has little or nothing to do with the Arduino.
That is a common anode device. You need to connect the anode to a 12V supply, presumably regulated. A 12V, 2 Amp switchmode supply would be the best bet. You feed each of the three cathodes through a resistor from a suitably rated NPN transistor (pick ones with a rated current of at least 1 amp) with its emitter grounded (to the same ground as the Arduino and the 12V supply) and drive the base with a resistor of about 1k from the Arduino pin you wish to control it.
You will need to determine the values for the resistors which feed each LED cathode from the transistor collectors. This is best done when you have the LED and the 12V supply. Connect the anode to the positive 12V and try a 100 ohm resistor from each cathode to the negative. Measure the voltage across the resistor and use this to calculate a new value to give 300 mA. Note that the resistors you finally use need to be rated for at least 1 watt.
No using a resistor to limit the current is not good enough for high power LEDs like this one. You need a constant current regulator, one for each colour.
Well now, is it good enough for a 1W LED?
Because these are actually three series chains of one watt LEDs, so the current control is the same task as for a single 1W LED.
I think if one followed the process I suggested - using a regulated 12V supply - and granted that I was being conservative by not taking into account the actual voltage drop of the LEDs at full power or the driver transistors, it would be pretty safe, if not optimised.
Now you could use the simple current limit circuit of a control transistor with its base-emitter resistor of two ohms in series with the emitter of the driver transistor and its collector to the base of the driver, to function as a constant current driver.
You need a constant current supply because the forward voltage drop of an LED changes with temprature. Power LEDs have a lot of internal heating so a simple resistor is only useful if you run the LED at much lower than its rated value.
Yes you could use a resistor in the emitter of a transistor but you would have to calculate it's value cairfully and make up that value from standard values.
UniFly:
Can you help me, I want to control very bright RGB LED. It's not programming question I just asking about voltage and mah.As you see, it needs 12V output and 350mAh for each led. How to realise this? Which Arduino/tools enough power?
Have a look at this project where I did exactly what your looking to do. I originally tested the LED and the constant current PSU using an UNO but built the final project using a ATtiny85
As others have already noted, you are best off using a constant current power supply. There is a bare board for sale at Tindie.com that theoretically would fit your LED. The components you'd need are easy to find. The PT4115 can be found on eBay as well for $0.40 a piece! As a whole this would make for a really inexpensive LED driver that would allow 12 bit dimming.
As noted by others, connecting the LEBd to a " normal" regulated power supply is not going to cut it. "Normal" regulated power supply keep the voltage constant. LEDs are constant current devices. LEDs, and particularly High Power LEDs such as yours get hot (you will definitely née a good heat sink!!!) and when the temperature raise, the forward voltage will also raise. That is why a simple current limiting resistor is not a good solution.
The LED that you have linked to has very short leads on one side, so perhaps look for an equivalent LED with leads that are a little longer. While the LED in your image is a common anode ( or cathode) LED, you can cut off the " bridge" to eliminate the problem and make it workable with the above linked board.
In general I personally would not trust these ultra cheap, un-binned Chinese mass produced eBay LEDs.
Grumpy_Mike:
Yes you could use a resistor in the emitter of a transistor but you would have to calculate it's value carefully and make up that value from standard values.
It is pretty standard stuff. This (cited by Riva here) is the current limiting circuit to which I was referring if you need something more than resistors, though I was supposing bipolar NPNs rather than FETs - much of a muchness.