Hello BLF,
Hope this project isn't too off-topic since this is a laser project, though I think it's still relevant since it's just as capable of driving LEDs. I had some time to do a short post about this project from the end of 2018. Thought some folks here may be interested in.
Here's what I'm calling Project 450 - a compact, simple, fully-integrated laser platform.
[Update - a small update with Project 450 - the copper block housing was changed to a much higher quality aluminium housing. Batteries were also upgraded to one of the best 16340 cells]
This project currently incorporates a 7W NUBM44-V2 450nm blue laser diode, which comes in a TO-5 can package, and as of writing, is currently the most powerful available visible wavelength laser diode.
This project focuses specifically on the design and development of the drive electronics in order to safely drive a constant-current load (such as this diode, or any LED for that matter), and is therefore applicable to all sorts of constant current loads such as LEDs for flashlights.
I would like to make it abundantly clear that I do not advocate the use of these kinds of laser diodes at these power levels since they are extremely dangerous and any mistake will lead to irreversible eye damage. I hope this project will be a good educational resource; please proceed reading responsibly. Laser goggles are always used (in this case a proper 5+OD for the wavelength googles are always worn whenever operated).
This project has two main aspects - an integrated, compact, single-PCB platform designed to be mounted on an aluminium extrusion as heat-sinking, and a 12A-capable true constant-current synchronous buck converter.
Integrated Platform
The integrated PCB measures exactly 50 x 100mm, making it fairly compact.
Power is supplied via two 16340 batteries, which essentially dictates the size of the product. In this specific scenario, the maximum drive current is only 4.5A at about 4.7V (~21W), and maximum load current on the cells is about 3A. As a result, the fairly mid-range quality EBL 16340 cells will suffice, though will be upgraded to Vapcell 16340s in the future, which will easily handle over twice the load.
For convenience, there is a charging circuit on board, which allows charging of the cells via micro-USB at 700mA. On board circuitry boosts the 5V from USB and charges the 2S battery via a dedicated Li-ion charging IC. For most 16340 cells, this results in a roughly 1 hour charge time from flat.
An Atmel microcontroller handles the entire system for various kinds of events. Here are a few features:
- Security Safety interlock requiring secret code to be entered via switches before system unlocks, impossible to turn on in a bag
- Constant current control with 4 programmable power modes
- Battery monitoring and low voltage cut-off
- Charge management
- Error codes via a total of 5 colourful LEDs
For heat-sinking of the diode, the switching regulators, and the battery charger, the entire PCB only has components on one-side, with exposed ground pads on the bottom. This PCB is then screwed onto a milled aluminium baseplate.
To prevent shorts, holes are milled into the baseplate for through-hole legs to sit in. A kapton sheet was then laser-cut to insulate all other parts, and thermal paste was then applied to the exposed ground copper pads.
A cutout allows the diode, housed in a solid copper mount, to be attached directly to the baseplate.
Synchronous Constant-Current Buck Converter
In order to drive the diode safely, a current-regulated driver is required.
There are several that exist today, the most powerful of which is the BlackBuck 8M Rev 3 by x-wossee. This is a 7-12Vin 1-8A constant current buck driver, using the IR3475 10A integrated SupIRBuck regulator. While a nice design, I thought I'd go for something with a little more power capability (not that we would need it). My original thought was to go with the TPS548D21, a 40A fully integrated regulator, but that's too excessive (and expensive), so I settled for a sensible 12A design instead, having about 50% more power handling capability than the blackbuck 8M.
The final design allowed me to layout the buck converter in a very symmetric way, which brings a tear to the eye! No consideration was made to make the layout as compact as possible, since the PCB had a lot of space. However, the main buck converter portion is very compact, and can likely be made much smaller for use in say flashlights or smaller hosts.
Testing & Results
Testing was initially done with a Cree XML2 LED to ensure correct operation and proper current regulation, before it was replaced with the laser diode. Frankly, it made a very nice, cute flashlight, so maybe I'll make this into a lamp in the future... To be honest I will probably not use this much at all since it's too dangerous, so it will likely have an alternate life as a desktop lamp. :)
Power levels were set to be (fairly arbitrarily):
- Threshold
- Bright (0.5W output) at ~600mA
- Powerful (2W output) at ~1.35A
- Turbo (7W output) at ~4.5A
Finally, the system was put together with a stock glass lens on the diode. The housing allows for a standard M9-0.5mm thread lens, which will be likely replaced in the future with a better lens. For now, a AR coated 405-470nm lens is used.
The result was as expected and the system runs very well. More result images to come soon later.
For more information, here's a detailed write-up: http://loneoceans.com/labs/project450/
Hope this was slightly interesting.
Cheers
:smiling_imp: “Ballz-eye!”