LED driver shield

Hi guys,

I am developing a shield to drive high-power and high-brightness LEDs, LEDs like those in the CREE XLamp and Philips Luxeon families. I think it will really help the development of high-brightness LED products capable of replacing standard incandescent and compact fluro products.

This shield paired with a Zigbee or WiFi shield also offers some really interesting wireless lighting possibilities.

Before I finish my design and get it fabricated, I am looking for some feedback on the idea and design, and also to see if anyone else is interested in one.

The design: 1) It's based on the LED driver LM3404 from National Instruments http://www.national.com/pf/LM/LM3404.html#Overview . 2) It will operate from a 24V power supply. 3) The shield will also include a linear regulator so that the LED driver shield and Arduino can be powered by a single supply.

Questions: 1) Does anyone know of anything similar? 2) Does anyone have any feedback/suggestions for changes or additions? 3) Is anyone interested in one once manufactured? 4) Does anyone have a good idea for a name?

Cheers Jim

Hey Jimmyh,

It's all above my pay grade but I believe the project is a great idea.

Best of luck to you.

Would you be manufacturing the shield or releasing it for DIYers to do themselves?

I ask because the IC you've chosen has a large (and important, thermally) GND pad under the chip, which might be tricky for average hobbyists to solder at home (unless they have a reflow oven, at which point they're probably not "average" hobbyists.)

What sort of LED count per shield and drive current are you planning on designing for?

I've been playing with HP LED drivers for 6 or 8 months and tried a few chips, so I'm interested in following your efforts and/or comparing notes. :)

I was planning on both manufacturing the shield myself and releasing the cad files for anyone to build themselves if they wish.

With a 24V supply rail I'm planning on driving up to 6 series connected LEDs with the LM3404 from National. If each LED is capable of outputting up to 180lm at 700mA ( http://www.luxeonstar.com/luxeon-rebel-es-led-neutral-white-lambertian-180-lm-700ma-p-454.php ), 6 in series will easily produce more light than a 60W incandescent bulb (around 800lm output).

The drive current I'm looking to use is 700mA, however by changing the passives, you can change the maximum drive current up or down. 350mA also seems like a sensible output current, however you can dim down to this current if needed.

The GND pad under the chip is a good point, but I don't know of another IC that has the features that I am looking for: 1) Dimmable 2) Small component count and low-cost 3) Variable output drive voltage without the need to change components - so it is easy to change the number of LEDs driven 4) Constant current LED driver rather than a constant voltage driver

ill_switch, what IC's have you been working with? Would one of those be a better fit, or do you have another IC that would work better?

Any suggestions/comments are greatly appreciated. I'm really looking for the simplest and lowest cost solution.

Cheers Jim

We have similar criteria as it turns out. Cheap, constant current driver that's dimmable.:)

I've been looking mostly at the following three ICs:

1) NCP3066 from OnSemi 2) ZXLD1366 from Diodes Inc 3) CAT4101 from Catalyst (now OnSemi)

I've poured my life's effort into designing a low-cost, home-solderable driver recently, since I'm going to need a few dozen of them for a project I'm working on and I want it cheap. Plus it's a really fun thing to do. :)

To date, most of my prototypes have been NCP3066. It's pretty robust, comes in easy packages, and you can run it boost or buck. In boost mode, it'll run 8 LEDs from a 24v supply at 700mA, pretty efficiently. It has a fairly high component count, but I don't think you can get away from that with a switching regulator.

Recently I've started working with the CAT410 chip. It's a linear reg but looks efficient if you keep the voltage drop to a minimum, by matching LED count and Vf very closely with your power supply. It's a little cheaper than the NCP chip and has fewer components. It's only available in a SMT package, but at least the thermal pad sticks out the top enough that it's really very easy for hobbyists to hand-solder.

Where your efforts and mine will differ is layout. Since I'm going to need so many, a shield is not practical. I'm making separate PCBs for the drivers, then will link them to PWM pin(s) on the Arduino for control.

If you stick with the chip you're thinking about now, people building your shield at home could at least just use conductive epoxy for that pad under the chip, I guess.