Slight change of direction. I've got several prototypes of this NCP3066 design up and running, and will use them on my big tank or the ATS when it's up, but I'm not convinced I want to use this design for ALL of the drivers I'll need, so I'm on the fence about ordering dozens from a board house.
For the people who have contacted me to get on the list for the "extras" when I order - if you're still interested, please contact me. I'll send out individual PMs in case people miss this thread. If people still want the NCP3066 design, I'll go ahead and order a bunch - I don't want to leave people hanging who were counting on getting some of these. The NCP3066 design does have the advantage of being through-hole for people that want that. Plus it's far more tested - I've actually been running it on tanks for a few months.
Otherwise, here's a different approach to driving LEDs, based on the ZXLD1366 chip someone mentioned a page or two back. This design is all SMT, and the chip can handle a lot more voltage, which means more LEDs per string. I'm aiming for 12 LEDs per string at 48v. (48v DC power supplies are available from digikey and other places for only a little more $$/watt than the 24v supplies everyone uses.) I put three of these circuits on a single 5cmx5cm PCB, so you'll be able to drive 36 LEDs per PCB. This design has some pricey components but cost per LED driven should be about the same. Since it's driving more LEDs per PCB, wiring on a large tank will be simpler. And, it's SMT, for people who like that.
This ZXLD1366 chip is a step down (buck) switching converter. The ADJ pin allows PWM or analog DC dimming, though it's pretty funky to use, since it needs a pretty narrow range (.3 - 2.5v or something) as analog, and wants the PWM signal to be in that range, too. If you leave it disconnected it floats to the internal reference voltage (1.25v) which results in 100% output - bringing it above 1.25v results in up to 200% output. To allow for simple dimming, as outlined in the datasheet, I've designed this circuit using a small NPN transistor to switch it to GND, so it'll work with the (5v) PWM signal from an Arduino or other microcontroller.
Otherwise it's really straightforward. There's only 4 external components besides the two required for my chosen dimming configuration.
Also, I put 3.5mm screw headers on this instead of the .1" pin headers I used on the other design, because there was plenty of room.
There's a separate PWM dimming pin for each circuit, though it would be easy to just use one PWM signal to control all three drivers, which is what I'll probably do for my tank. With 36 LEDs per PCB, I'll only need 6 PCBs for my whole tank! This simplifies wiring compared to using THIRTY SIX buckpucks, or 18 meanwells!
This is still in draft stage. I'm planning on getting a prototype board made soon, and I'm ordering components later today, so I'm hoping to have a prototype up and running soon.
Here's the sloppy schematic:
And the board:
I tried to follow the layout guidelines in the datasheet regarding which components to put close to everything else, but it's just so dirt simple it wasn't very hard. I used a ground plane on both sides with lots of vias near the ICs to help with cooling. Chose the trace widths to allow for 1A per driver with a little headroom. I will probably run these at 500 - 600mA, since I may end up with some LEDs that have a 700mA max (Cree MC-Es).
As always, comments or suggestions to improve are welcome. I'm working out the BOM now and will post soon.