Hey all
Someone recently asked me to make (or find )a buck driver to power the CBT-140. 2-3 li-ions will be the voltage. Also 2-3 brightness levels are also preferred.
The space we have to work with is 32mm diameter and 50mm long.
I am open to suggestions :)
What’s the VF of the CBT-140? My BU_CK could probably handle it, not sure tho.
Edit: http://www.luminus.com/products/Luminus_CBT140_Datasheet.pdf
3.6-4.2.
Gotta love the low Vf at 25A
FET driver from RMM. Cells (parallel) could possibly limit LED current.
You don't need a buck driver with those big boys, unless you want limited/regulated output.
That said, there is no buck driver I'm aware of that will fit in a flashlight that can handle 20A, or anywhere even close to that. Maybe with a 50mm depth you could do it, since the inductor would have to be enormous as well as the flyback diode. It is definitely far outside of the realm of anything I've ever seen done in a flashlight with a buck driver. Not saying it can't be done, but it isn't something that you can just put together and hope to work on the first try. The LED is tough enough that it can probably handle a ton of extra voltage ripple and abuse so you've got some margin there, but at the same time experimenting with new buck driver designs on a $100 LED isn't something for the faint of heart.
IMO a well heat synced direct drive is the way to go, since it is simple and you know that if the wire connections are done right (HEAVY) it will work, and work reliably without blowing LEDs.
Unless something changes soon, I don't believe that Luminus will overtake Cree anytime soon for most of our lights. The efficiency stinks and they are a lot more expensive. For a mega thrower where heat, cost, or battery life isn't an issue, sure, they offer something there, but for a normal light the gains just aren't worth it. I know that it sounds cool to be able to draw mega amps, but in reality it just isn't that practical for most lights.
Similar question is bothering me this days, what driver to use for powering Luminus PT54 red led. Somehow I thought this led Vf is about 6V but today I finally found datasheet and imagine my surprise when I saw that the typ.Vf for PT54 is 2.7V … I am thinking something like zener-FET driver (I think this is the one I want), only question is whether it can push 8-10A…
CBT-140 is a kick ass beast for itself, must have costed some serious $…
Sirius, I believe a 7135 based driver would be better suited for driving a low Vf LED from a LiIon. Not too sure.
I would use a regulated driver, similar to my PT-54 red build running 37 chips for 13.5+ amps. Works really well, but if your host is 2-3 batteries in series (mag?) then you might want to try a HX-1175b. It will definitely have some ripple modded (proven to run MT-G2s at 13.5A), and you will have to settle for lower amps.
Luminus LEDs can run cool to hot in a matter of a few amps, so if a FET doesn’t overshot the recommended current by much it is the easiest route.
For a low Vf led it might be a good idea to drop a chunk of the voltage with a high wattage resistor and let the 7135’s only have to account for ~1V.
Run my fet switched green PT120 maglite aspherical direct drive with 4D Tenergy 10,000mah NiMH batteries. According to Lambda data this setup is capable of 30A fresh off the charger. The real beauty of NiMH is the long flat discharge power curve.
My easiest red PT54 maglite build was using the stock switch with 18ga wire soldered to emitter negative, heatsink providing positive ground (install batteries backward), 2 Tenergy D NiMH batteries, copper braided tail spring. 9A to the emitter and decent run time. Modes? Don’t need no stinkin modes!
Thanks for the update guys, 7135 are even better solution, they offer more simplicity I just need to get 30 more 380mA chips 
and a slave board for them all 
Just blew up my last SST-90 using BU_CK with a stack of two .01ohm 2512’s!
Happened to fast to get a current reading, only a few seconds, but to blow an SST-90 screwed to a 2Lb block of Al takes some current.
Don’t even care I’m out $18!!!
Welcome to the club. 