In my project, I use 64 RGB LEDs for a LED matrixs. I use row and column approach to drive an individual LED. i.e. I use NPN transistor to give input to the anode and ULN2803 for the cathon. And use the MCU to give the signal input to the transistors and control the LEDs.

I can drive the matrix to display words, however, if i try to switch on all the LED at the same time, (i.e. 64 LEDs all R,B,G color, this time i give signal to all the transistor, hence all the transistor switched on and all the LED light) the problem occur. I notice that the LEDs are not bright enough (I need it for outdoor use, a lighting system). I also notice that the LED's brightness are not the same.

I tried to connect the LEDs in parallel and give 3.6V to them with a very small resistor 10Ohm, they will have the acceptable bright, with around 3.8A, around 20mA per LEDs. And the brightness are almost the same.

However, I must use the broad matrix for the design (I need to use for lighting and information display at the same time) and once I know that if I connect them in a matrix, I cannot switch with 3.8A as the IC may burn. Any one can help?

Thankyou very much.