I need to build LED strip by using 20 RGB LED Piranha.
This strip I'm going to connect to LED controller.
Controller has 12VDC output with many color changing options.
Please help with circuit.
Thank you.
Controller takes 12VDC from the power supply and has Vcc, R, G, B outputs. Controller is able to perform different color changing modes ( flashing, dimming, fixed colors, etc).
Do you need more information?
OK, so try connecting up just one RBG LED like this:
The common cathode of the RGB LED is connected directly to Vcc.
Each of the R,G,B leads needs a 430 Ohm resistor on it.
I derived this current limiting resistance value by using the values in the datasheet for Vf (Forward Voltage), and the voltages that you are measuring:
Rlimit >= (Vsupply - LED_Vf) / Desired_Current
Rlimit >= (14v - 3.4v) / 25mA
Rlimit >= 10.6v / 0.025 Amperes
Rlimit >= 424 Ohms. 430 Ohms is the closest standard E24 value of resistance that is greater or equal to 424.
Table of standard resistance values is here: http://www.logwell.com/tech/components/resistor_values.html
Thank you for your effort. I've forgot to mention that I've connected that way only ONE RGB LED to the controller and it works great. I need to build a circuit for 20 LEDs, which will work from the same controller.
You're welcome. If you find yourself "stuck", post again. If you get it working, why not post photos here, or make a video and post it on YouTube or someplace and post a link to it.
Bill,
That's all great info, but unfortunately with his current project he can't really use anything more than the formula for the current limiting resistors that I've already posted.
His RGB LEDs have 4 pins; a common anode and one each for Red, Green, and Blue.
There is just no way for him to use these RGB LEDs in series, nor to cut down on the number of resistors that are required - unless he wants to risk thermal runaway and subsequent melt-down.
I suspect the current regulator info could be handy, which covers sinks as well as sources.
His LEDs are not going to drop the same amount of voltage for each, which means one size for all resistors isn't really that appropriate. I've been pretty busy at work, but I also have the impression he may want to make it variable, though I could be off on that assesment. I've been meaning to redraw the standard transistor model I have using a LM317 as a voltage reference.