atmegaledrgbtransistors
I want to be able to control 9 RGB leds, each color from a potentiometer.
Each color needs 20mA, so when all the colors are present the leds will need 540mA (9*3=27, 27*20mA=540mA).
My RGBs leds are common cathode so between the micro controller and the anode for every color y will put a transistor(TIP31C), with this configuration:
Do you think it will work? or I will need another voltage source? since I am giving just 5v to the micro controller.
Thanks for any advice in this project.
Since this is a constant-current sink IC, no resistors are needed in series with the LEDs.
The current is programmed using a reference resistor connected to one of the pins that sets the reference current used to drive the LEDs, and it is the driver chip's responsibility to make sure the correct voltage and current is applied to the LED. In practice, I have found this works well.
You could add a resistor in series, but this defeats the purpose of using this chip. It will increase your part count, increase your minimum VDD requirement, and if you need to increase VDD, then you will waste additional power.
Below is the figure used to determine your reference current for each resistor from the datasheet:
If you power off 9V then consider using some of the 3W LEDs in series: -
Typically red leds need about 2.5V across them so wiring three in series will need at least 7.5V then there should be some current limiting circuit that might take 0.5V.
Typically for blue or green leds they need 3.4V across them so maybe only series together two LEDs.
You might just about get enough brightness with the NCP5623 chip this way but if not you'll need a current limit circuit and mosfets. The NTD80N02 looks OK but you need to limit current into the LEDs.
Best Answer
Yes, this will work, but don't forget to use different resistors for different colors, because each color has different voltage.
But my opinion is to connect LEDs serially and use higher voltage (but you need to use other LEDs with NO common wire) then you get much better efficiency like example:
simulate this circuit – Schematic created using CircuitLab