Help making a high powered RGB Lighting system for my highschool

The LEDs use 33V max, so you plan to use 36V? Seems like planned overstress to me. Something has to dissipate that extra voltage.

Pay attention on the recommendations for the unused channels also (for your future expansion).

Watch this in your PCB layout: "The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should then be connected to an internal copper ground plane with thermal vias placed directly under the package to spread out the heat dissipated by the LT3496." "The exposed pad of the package is the only GND terminal of the IC and is important for thermal management of the IC. Therefore, it is crucial to achieve a good electrical and thermal contact between the exposed pad and the ground plane of the board."

charliehorse55: Switching plans again. I found this beauty of an LED driver:

http://www.newark.com/linear-technology/lt3496ife-pbf/ic-led-drvr-tssop28/dp/07P8434

Three individual 750mA PWM outputs.

I will construct one PCB per light, and then use a terminal block to split the PWM signal from the Arduino. That way, If the lighting array needs to be expanded you can simply add another board and wire it up.

I'll also be using 30W RGB LEDs, they take 28-33V in, so I will use a +36V PSU.

Thoughts?

Obviously, you didn't read what I wrote carefully. LT3496 is the chip that I used in the high power RGB LED shield. Again, I already published the design of circuit. You can just use driver part of the shield. http://arduino.cc/forum/index.php/topic,51887.0.html. You can not hand-solder LT3496, it has to be reflow due to GND. You have to find someone can do it for you. If you make only three of the driver, total cost of whole thing (PCB, parts, and assembly) will be likely higher than cost of three shields.

I did read what you posted quite carefully, I just didn't catch the exact chip name. I will be running 6x 30W LEDs from 6 separate PCBs.

Also, I want to design my own circuit as this is a school project and I need something for the teacher to mark.

Finally, your circuit did not implement the Open LED protection feature of the chip, which I will need with my setup as it is entirely possible that someone leaves an LED string un-attached.

Your circuit will help though, I will modify it to my needs.

Thanks.

Open LED protection is not necessary for buck design unless you want to arbitrarily limit the output voltage. It is over voltage protection(OVP) for boost and buck-boost design. Run the circuit from LTspice, you will understand what it does.

Thanks again. I thought that it didn't make sense for buck but thanks for confirming. Makes the circuit a little simpler.

EDIT: And what is the maximum input voltage for driver? A 48V input would work great for my needs.

charliehorse55:
EDIT: And what is the maximum input voltage for driver? A 48V input would work great for my needs.

As in data sheet PVIN max is 45V. If you use same power for VIN, you are limited to use 30V.

Okay, I guess I'm stuck with the slightly more expensive 36V/300W PSU.

I assume the actual driver IC doesn't use much power so I can simply use two 200m ohm resistors to make a voltage divider for it to run it off the +36V?

EDIT: That won't work, but possibly with higher ohm resistors? I doubt the IC draws more than 2-3W of power anyways.

There are reasons why people don't use a simple voltage divider as a voltage regulator. It is not matter of efficiency. If you use high ohm resistors to reduce the resistor power dissipation, there are high voltage drop across the resistor depending on current draw. When LT3496 draw varying current especially during PWM, you will have huge fluctuations on VIN.

Right, so a 12V VRM is a better idea.

Why 12v? You want to use as low as possible, If you are going to use switching voltage regulator. Linear voltage regulator won't work, because of high voltage difference between In and out. I think you can use 5V from Arduino, anyway you need to power Arduino with lower than 12V.

I was going to power the arduino through the USB interface. The only thing I’m going to be doing is driving 6 PWM outputs and 6 digital outs, no LEDs or other devices. The 2.5W a USB connection can draw should be enough for that right?

Unless the driver IC uses <0.25W each, I won’t be able to run them off the Arduino because I will be using 6-8 of them.

USB power may not enough. Computer USB supply normally 500mA max, and LT3496 need 80mA max based on my measurement. You can just buy 3.3 or 5V power adapter.

Okay, I have done a major re-work of my driver board.

I am going to use the same LT3496 driver, but in boost configuration so that I can use a +12V input. This will also negate the need for a separate 5V power supply as the LT3496 can be run from 12V without issue.

I have also decided to switch to an I2C interface. I’m trying to find a chip like the ATTINY85, but runs from 12V. If that’s not possible I can always power the chip from the Arduino as it takes <3mA at full load, but it would be much neater and easier to use a chip that can be run from the main +12V connector (that comes from a computer powersupply).

I have now figured out that I will need a 5V source for that ATTINY85 so I have decided to use the +5V rail from the powersupply and power each board with a molex connector.

Should I power the LT3496 with +12V or +5V? I have access to both on the board.

Also, is there a way to flash the board so that when it is not plugged into a computer it executes some simple code? I am going to attach some 10k pots to the analog inputs and I would like the board to automatically read those values and run the lights accordingly if no computer is plugged into to control them.