HI,
IM TRYING TO FIGURE OUT IF I I NEED TO CONNECT A RESISTOR TO THE R G B PINS ON A COMMON CATHODE LED.
OR
IS IT THAT I ONLY NEED 1 RESISTOR IF I HAVE A COMMON ANODE LED?.
PLEASE HELP BEFORE I WIRE UP 100 LEDS TOGETHER
THANKS
I INTEND TO CONNECT 100 5 MM RGB LEDS TO AN LED CONTROLLER WITH COMMON ANODE CONNECTION.
Yes, you will always need resistors with any LED. For an RGB LED, you will need three resistors. You may find that the value (in Ohms) of the three resistors are not quite the same. This is because the blue LED has a larger forward voltage than the red and green LEDs.
You can't share a single resistor between all three LEDs in an RGB LED. Unless, that is, you only ever light up one LED at a time, which is a big restriction. Even then, tou would need to choose a single value, which would not suit all three LED properly. Much better to use three separate resistors.
Some LED controller chips actually control the current using a transistor built inside the chip, so you can connect the LED directly without any resistor. Of course, a no-resistor connection should never be attempted on a chip that doesn't specifically include such a feature. Usually chips that do require a single "reference resistor", which connects to a dedicated pin rather than to any LED.
Had you giving the specific LED controller part number (or better yet, a direct link to its datasheet), this message probably would have been much more helpful.....
THIS IS THE LED I HAVE DECIDED TO BUY.
THESE ARE THE CONTROLLER I AM THINKING TO BUY
http://www.bigclive.com/rgbcont.htm
THANKS
Hey ANIL I recently bought and built the exact same kit from bigclive.com. I would highly recommend it. The kits are quality and easy to assemble. Clive is a good guy too. He ships stuff real quick and if you have any questions hes real good about responding to emails quickly.
If you are using PWM or multiplexing it won't be necessary.
Check out my LED Array using 74HC595N's and no resistors...
Check out my LED Array using 74HC595N's and no resistors
If you are driving an LED and not using a resistor or any other intentional current limiting device you have a bad design and although it might work you will be stressing some components in the system outside its absolute limits. This means that while it works now you will be overloading something in the circuit and operating the components outside the recommended limits. Normally this will result in something burning out sooner or later. In your case you are probably stressing both the LED and the 595. It could be that the LED can take the peak current that is being limited by the 595 but you are stressing that.
Just to say it works is no justification in saying that this is a valid technique, especially when beginners can so easily pick up bad (or even fatal to LEDs) habits.
So an LED always needs a current limiting component, which is normally a resistor.
Sorry Sir :-[
I should think so 