high power led driver

Hi, I’m trying to build a circuit to control some high power LEDs thru arduino.
The LEDs need about 350mA, current regulated. I’d like to know if there’s an IC that does current regulation (to drive the LEDs) and manages the LEDs (I have 5 of them). I know there are many, but I need about 350mA per LED and that’s a lot I think… any idea?

interesting.. but it's only 1 LED on that IC, do you know if there's something similar but that drives many separate LEDs independently?

snaggy:
interesting.. but it's only 1 LED on that IC, do you know if there's something similar but that drives many separate LEDs independently?

Well one driver can drive several leds if they are wired in series and the drive has an output voltage higher then the combined voltage drop of all the series leds wired in series. However if you want to control each led independently then each would require it's own constant current driver.

Lefty

I have an article on driving 350mA LED's on my website:
http://www.elcojacobs.com/using-shiftpwm-to-control-350ma-high-power-leds-with-arduino/

Take a look at these

BillO

reply #7

Boffin1

Super cheap, super easy. Use a decent wattage resistor, 1/2 watt or more, or calc out the dissipation. The circuit isn't particularly efficient (3v drop) but it is cheap and easy!

Basically the LM317 acts as a variable resistance limiting the current. The chip is rated for 1.5A, I'll say that if you are driving more than 500mA you NEED a heat sink. These are great with a 1.2 ohm sense resistor and connected to 12-14v, it's perfect for driving the 10 watt white LEDs (1A@9-12v) you can get for a buck or two on ebay. The LM317 is one of the cheapest components you can get, and one of the most useful too. Buy a pack of them, you are going to want more.

This feeds into the LED, and you switch the ground connection with an NPN transistor to provide PWM.

I've made a bunch of these.. if quick and dirty is good enough, it'll do the job nicely :slight_smile:

Here's the Application Note from ON Semiconductor on using the LM317 this way:

The TLC5940 http://www.ti.com/lit/ds/symlink/tlc5940.pdf can provide constant current
upto 120mA per output (set by single resistor for all outputs). As it has 16 outputs you can parallel
them in threes to give 5 outputs of upto 360mA, and you can program PWM values into it for dimming
(and store them on on-chip EEPROM!!). Only one device for 5 LEDs then.

You'd need to be very careful not to exceed the power dissipation though - perhaps adding enough series resistance to keep
the outputs around 1.0 to 1.5V (below 1.0 the constant-current behaviour deteriorates, the higher the voltage
the more heat).

Another constant current driver Arduino Forum

Thanks to you all, in particular the TLC5940 seems a good solution, I hadn't realized I could use more than one output on the same LED. @MarkT, could you clarify this part a bit? would I just need to wire the 3 outputs together and set the same pwm on them? Or maybe I need some capacitors to smothen things up (random guess :P)

Thanks

350mA,

That's hardly "high power".

3.5a? maybe.

dhenry:

350mA,

That's hardly "high power".

3.5a? maybe.

It's all relative DH, after a newby is done blinking his 20ma standard leds, stepping up to a 350ma led is a 'higher power' step up in my book. It's where you have to learn about good constant current control methods and proper heatsinking and wearing sunglasses if you are going to look straight at them.

Lefty

snaggy:
Thanks to you all, in particular the TLC5940 seems a good solution, I hadn't realized I could use more than one output on the same LED. @MarkT, could you clarify this part a bit? would I just need to wire the 3 outputs together and set the same pwm on them? Or maybe I need some capacitors to smothen things up (random guess :P)

Thanks

Well I am not sure - its possible they have separate counters for each output (though this seems wasteful), so you would need to
double check that. Since the currents add even that might not matter. Yes, set the PWM values the same for commoned
pins would be sensible.

I bought one and will try.. but what do you mean by "separate counters"? I know I can set the current individually using the DC (dot correction) registry in the tlc5940, so yes each pin has it's own separate current regulation I guess.. but anyway as you say currents do add, as long as the voltages are the same (and don't flickr I guess..) there shouldn't be any problem.

A word of caution, while you can get the current within the rating of the chip watch out for the power dissipation running 5 350mA LEDs is going to be very close if not over the limit.
There is a scary looking formular in the data sheet, that needs your circuit values plugging in.

As for our Mr Heny, I don't cair what you call high power, 350mA for an LED is high power. It might not be ultra high power but it is high.

Its kinda relative, 350ma, is a little more than 1/3 amp, which is a lot for a microcontroller, but insignificant if you are talking about a car alternator, and a lot more insignificant than the smallest circuit breaker in your home.

Clearly the microcontroller wont be enough to run one LED, so you will need power supply for the LEDs, but you may also need to consider heat, those LEDs will probably produce some heat that you may need to consider depending on how you are using them.

You'd be surprised how little heat they generate- but they should be at least on one of those aluminum "star" heatsinks, running the raw LED "bead" without a heatsink for more than a few seconds will in fact cook the little beast. On the plus side, one watt white LED's are less than a quarter each ordered from China.

I have had good luck using aluminum angle bracket and channel from the local Home Depot for heat sinking, and a tube of white lithium grease for compound.

I have a homebrew LED photo strobe with over 140 watts of LED's on it now- I use a "repurposed" aluminum cable modem casing (about two pounds of thick aluminum) as the heat sink of the gods on that one.

On the subject of Power Supply- simple. ATX computer power supply, ground the "power good" line and you have a high-capacity 12v and 5v supply... fan cooled, and cheap.. free, if you cannibalize an old PC... Use a fuse though, PC power supplies can kick out quite a bit of current!

Judging by the type of LED that you have linked to in your first post, which is a RGB LED you are not dealing with 5 LEDs but with 3x5 = 15!

If, on the other hand, you want to control the brightness of these 5 LEDs independently then things get more complicated.

There are quite a few chips available that can control 3 channels at a time but finding one that actually has a good dimming ratio at high current is not that trivial. But, it depends on what you actually want to achieve.

Te LT3496 can control 3 channels with up to 750mA each at a dimming ratio of 1:3000. I have not been able to find anything comparable. But then, that certainly will not result in a low cost solution, as that chip alone is around $7.

Hi guys,
I’ve read LT3496’ datasheet and surprisingly see that it needs a lots of additional MOSFEts to work, according to it (see attachment).
Please advise the simplest way for dimming 3W RGB LED, I’m a newbie and my experience with ICs and soldering is very poor ))
I need 3-channel independent and smart dimming.

LED SPECIFICATIONS:
Model Name: CREE XML RGBW
Emitted Color : RGBW/RGB White
Product Voltage: Red 2.25~2.6V, Green 3.3~3.9V, Blue 3.1~3.7V, White 3.1~3.7V
Maximum Drive Current: 1A
Maximum Power: 12W
Max Luminous Flux: Red 87.4LM, Green 114LM, Blue 39.8LM, White 100LM
Viewing Angle: 130 Degree
PCB Diameter: 20mm

Thank you in advance!

CREE XLamp XM-L RGBW 12W.jpg

Talking about high power, the '100W' LED arrays take about 3A at 22 to 33V (depending on colour).
The green/blue/white ones are close enough to be feasible to run from a 36V supply with some
series resistance of constant-current driver - a power resistor is a cheap and simple solution
when the voltage is a close match as you already need a heatsink for the array. The advanced
MOSFET boost/buck constant current drivers are significantly more efficient, and control the current
better, but not so cheap to source.

When you have enough LED power you have to worry about cooling - 12V quiet cooling fans are
easy to source, so a 12V in constant-current DC-DC converter makes sense for powering LEDs
(a lot of LED strips are 12V anyway)

PWM is an easy way to dim LEDs but there are issues - not all constant-current drivers are suitable
to PWM at high enough frequencies to be flicker-free, and if you are using a lot of power you can
easily end up generating significants amounts of EMI if you don't take care.