Extremely Simple 5V Ultrabright LED Light

I was talking it over with the saikoLED team a few months ago, and we realized that there's really nothing out there for doing ultra high brightness LED work that is super cheap and has an adequate passive cooling solution. In order to deal with this, we came up with a new design that is sort of the "Honda Accord" of LED lights as opposed to a Cadillac that we've generally done before.

This light is extremely simple -- a case that has a hole pattern appropriate for a 20mm LED Star Board (either Luxeon Rebel stars or the LEDEngin 5W LEDs should work great), a hole pattern to attach a chassis mount power resistor for current limiting, and some mounting holes. In this case, the mounting holes are either three #8 screws (or eye bolts), or two 1/8" NPT holes suitable for using with the LOCLine line of flexible hollow connectors. I really like the idea of the LOCLine connectors as they are essentially super cheap plastic goosenecks that the wires can all be run inside.

After this, you simply connect up a 5V power supply to provide an attractive, cheap, and quite bright LED light fixture. By purchasing a power supply with variable voltage output, you can also easily dim the LED by varying the voltage between 3 and 5V, or use a supply that can output 5V with a PWM for brightness control. However, the goal here was simplicity, so the assumption is that this might be used to make an alcove a pretty bright color as opposed to a fading RGB light fixture.

That said, it would be relatively simple to use a RGB tri-color 20mm LED board in this fixture along with some external electronics for fading. Most of the goal here is to have a nice case and mounting option for LED lighting so that cooling is less of an issue.

Step 1 Case Design

The case is designed to be manufactured easily using eMachineShop.com. All holes are straight through, the case is 0.062" aluminum, the holes are tapped as appropriate, and after receiving them I took a lot of 40 or so to be anodized all at once for $60. The 3D structure is made using the CNC Bending option, which produces a case that has a nice 30 degree or so taper without needing any expensive internal milling.

Inside, the hole pattern for the star board is centered, and the hole pattern for the power resistor is off to the side with only four total solder junctions to worry about per light. The screws for the LED are #4-40 while the resistor uses #2-56 aerospace screws. The two larger visible holes are both tapped 1/8" NPT holes for use with LOC-Line flexible arms, but otherwise are simply the hole to allow wiring to be taken outside of the case while mounted either in a hanging fashion using #8 eye bolts, or from the side when fixed directly to a surface such as an aquarium canopy.

Comments

[cpotoso]

Using a resistor to limit current is simple, but wastes a lot of energy as heat. Perhaps using a switching device like the following link (for only $2) would be advisable.

http://www.dealextreme.com/p/18v-5w-cree-circuit-board-for-flashlights-16-8mm-5-5mm-26110

[neltnerb]

This is an excellent suggestion, and a great price for a constant current buck regulator. Thanks for the link!

For anyone interested in a more integrated system, I have circuit schematics for use of the national semiconductor buck regulators on my saiko 5 instructable. You can also purchase current sources from meanwell for good prices that could run up to 5 or 6 of these in series!

In this case the goal was low price only, thus no custom pcb.

[neltnerb]

Have you used the linked part before? If it has any kind of sane mounting options, I would be interested in including tapped holes for attaching it to this case in my next revision. However, the product page doesn't seem to have a datasheet and the images, while it looks like there might be some holes, make it look like the holes are probably not okay to electrically connect to a case.

Best,
Brian

[cpotoso]

Sorry, I've never used this part before but have bought things from DX in the past and been happy with them. Be aware that it takes a loooooooooong time for them to send things (1 month is typical), but since the s&h = $0, I am not too worried. I really like the idea of these switching regulators, they are really cool, but have not used them (other than in pre-made power supplies).

[neltnerb]

Thanks for the information, and the heads up on shipping time.

If you find that you want to get into building your own switching supplies, I *very* highly recommend the National Semiconductor parts such as the LM3404, LM3406, and LM3402. They have an integrated MOSFET so you don't need an external transistor (a source of minor headache if you don't know anything about power transistors already), they are rated at up to 1.5A at 72VDC, and the design tools offered on the National Semiconductor website are *amazing*. Literally, it's as simple as telling it which LED you're using out of their database of thousands of choices, how many you want in series, how many in parallel, what current you want to operate at, and it literally designs your entire circuit for you -- including a parts list of digikey stocked parts. It's amazing, and great for beginners in power supply design!

It even has built in spice simulation so you can see how well your system will perform, has the option to swap out among a list of valid parts if you want to make it so that multiple designs share components, and you can order their prototyping board if you want to try it out. Their prototype boards are a bit on the large size due to the need to fit any application, but if you're at all nervous about whether it will work in a custom PCB the price for their prototype board is far less than even the $33 each student specials for boards from Advanced Circuits.

Best,
Brian