Hello to everyone! I am writing on this forum as I am having difficulty finding the right component for my needs.
I'm looking for an LEDs driver with an I2C-compatible control interface.
I have to be able to individually address a large amount of RGBW LEDs, 250 to be precise. Moreover, I want to controls LED luminance with a pulse-width modulation (PWM) scheme.
So far so good, the problem is that the LEDs that I am using (Cree® XLamp® MC-E LED) have a DC forward current of 700 mA. So I would like to find a driver that can guarantee an output current of 350mA.
I have checked in several sites but have not yet been able to find a driver capable of giving this output current.
LauraBentivoglio:
I'm looking for an LEDs driver with an I2C-compatible control interface.
I have to be able to individually address a large amount of RGBW LEDs, 250 to be precise. Moreover, I want to controls LED luminance with a pulse-width modulation (PWM) scheme.
Can you explain these requirements further? They sound very difficult to achieve. For a beginner, almost impossible.
250 RGBW LEDs controlled by PWM though i2c interface means 1000 PWM channels. I have heard of I2C chips with 48 PWM channels, but you would need 20+ of those. The chips commonly used in Arduino circuits have only 16 PWM channels so you would need 60+ of those chips, so you would also need an i2c multiplexer chip also, because you can't have 60+ chips on the same bus.
In addition, you will need 1000 constant current driver circuits with PWM inputs. Perhaps you can find CC driver circuit boards with 4 channels per circuit. I have only heard of 3-channel CC driver boards.
So I don't think this project is suitable for a beginner. Maybe start by learning to drive 3 of your LEDs. This will give you time to practice building circuits and coding and time to find the best components. When that works, think about 30 LEDs, then 250.
You are right, the overall goal is quite complicated.
Actually by now I would just work and test with a smaller number of Cree® XLamp® MC-E LEDs, let's say 10. ( I will follow your suggestion of starting with 3 and increasing then the number )
For the moment the important thing is to test and practice with I2C bus communication and to be able to vary the brightness of the RGBW LEDs using drivers with PWM outputs.
The problem I am having is that of finding a driver with an I2C control interface compatible with these LEDs, hence able to guarantee a current of at least 350mA. In most of them the current is up to 100mA and I cannot change the LEDs.
In the meantime, thank you so much for your clarifications.
Sure! What I need to be able to do is to create precise lighting patterns of a quantity of RGBW LEDs.
For now I have used Shift Registers and arduino to go and command them. However, now I am interested in bus communication and in these drivers that are able to modulate the outputs via PWM (e.g. https://cdn.sparkfun.com/datasheets/BreakoutBoards/lp55231.pdf).
At the moment what I would like to do are just simulations to evaluate how LEDs behave with this type of approach and to do some practice.
To command 5 RGBW LEDs for the moment is enough for me. However, I need them to be individually addressable.
Suggestions on where to find a compatible driver with my LEDs?
Thanks!!!
I have not seen any single driver modules with such high current and i2c interface. I imagine you will have to find constant current driver modules with pwm inputs, and use an i2c chip with pwm outputs to control the CC driver modules. PCA9685 would be a good i2c chip to learn with. You can get modules like these. It has 16 PWM channels and is widely used in Arduino projects, so there are libraries and lots of example code. Then you will need constant current driver modules such as these, but they only have 1 channel each, and you will eventually need 1000!
I've looked at the photos and it is great! It seems that you know a lot about LEDs drivers and I2C chips. Have you got some suggestions on which LEDs driver buy to work with a PCA9685?
I've seen here that version 12 of this board from sparkfun increase the maximum current to 660mA:
Yes, that - being version 12 - does appear to be perfect for the purpose. 660 is close enough to 700 mA that you would never notice and in any case, it makes sense to under-run them for durability.
So, 250 RGBW LEDs, 1000 channels, you will require 334 of them at a discounted price of $4,529.04 - according to the Sparkfun website.
I will think in future about a new cheaper solution to drive that big amount of LEDs
By now I will just practice with the I2C communication and PWM outputs.
I have used the PT4115 LED driver with the PCA9685 PWM chip. These cheap boards also seem to use that chip.
LED current is set by a current sense resistor (formula is 0.1/R).
350mA boards have one mounted, 700mA boards have two.
I doubt you can keep heat under control with 4*700mA (~8watt) through an RGBW chip on a star base.
Leo..
