There is a single switch variant of the buck-boost topology. It inverts the output voltage, but that should not be a problem.
Hmm, firmware guy . . . you are not by any chance into DSpics and desperately want to implement synchronous rectification in SW? 
DSPics? I just threw up a little when I read that :Sp
Never was a Microchip fan, I have used them enough (16 and 18 series) but never really appealed to me.
These days I’m a little biased though, current employment and all 
Sorry that I disturbed your stomach.
I’m not a Microchip fan either. But some of the DSPics have dedicated hardware for smps. The only others I know with those features are within the Ti c2000 family. That’s even more exotic, at least to me. 
Synchronous rectification is so nice I would even touch a Microchip part for that.
Are there constant current boost drivers that can deliver 3A from 2xAA?
Last time I looked (several years ago) you had to use a high current fixed voltage boost regulator, sense resistor, and an op amp to make it work as a constant current source. You multiplied the voltage from the sense resistor with the op amp and then used that as the feedback voltage for the regulator.
Maybe I’m missing the target here? 3-6V 3A to power multiple LEDs in series or what? 3-6V to power a single LED with 3A needs a buck/boost.
If possible, include compatibility for 2 & 3 NiMH/alkaline and you'll really have something special here. 3 NiMH shouldn't be a problem, and even if it has reduced output with only 2 NiMH, that'll still be far ahead of what's available now.
I’m not aware of any. Most capable of that current have an undervoltage lockout of at least 2.8…3V.
But one could convert a voltage regulator in the way you described. Would probably fit on an 16mm veroboard cutout if you have a calm soldering hand.
Yes, perfectly right, the driver needs buck/boost capabilities. (but hasn’t to be of the buck-boost topology)
This one from Fasttech has the specs to do 3A, but it’s been out of stock since January. I’d like to get one, just to see if it can do it. I suspect that it can only do 3A when running on a full charged Li-Ion. Since it is output voltage adjustable, there has the possibility to run two emitters in series.
Too bad it looks like they will probably not get any more.
Relic, I just submitted a request to FT for the driver you mentioned.
Its been awfully quiet over here. Does anyone have any more ideas or strategies? Please dont give up trying.
What about that 1A boost driver that was looking to scale to 3A in a future iteration?
Hey, who’s talking about giving up?
I jotted down a few ideas I want to try out on my ‘when I finally got some freetime’ list, but unfortunately I will not be able to build anything within the next 6…8 weeks.
If this is not done by others in the meantime, I will happily contribute what I can after that time.
So, here is the circuit I'm using in a custom light. This isn't intended to be the solution to this thread - I was just asked to upload it...
Yes it's complicated, and may not PWM well, but it does work for my intended application. Which as I stated earlier is 2amps maximum.
Feel free to comment and question!
A HUGE thanks goes out to all the intellects for your energetic participation in trying to come up with a solution. Your efforts are imensly appreciated. I think the need and desire for such a driver has been well established. Regardless of who or where the driver is manufactured and sold, I believe it will sell in high quantity if it can remain affordable. While we have an unreliable claim of a possible driver larger than 17mm being able to provide good boost results, (for obvious reasons) the 17mm target size still remains the goal until all other options have been exhausted.
Aside from the huge physical & intellectual challenges, I also realize that this isnt something that can quickly or inexpensively be thrown together and tested. The hurdles are enormous, but yet we have members that still arent willing to give up trying. THANK YOU!!
Please, if there are others that have more ideas to add to the discussion, please feel free to join in. If you wish to keep your ideas private for a possible joint venture, please do PM others with your plans and ideas if you think it will help. My initial thoughts about surrendering a design to a chinese manufacturer for production was simply in the interest of keeping it affordable to the masses. Looking ahead: if anyone can have these made by a preferred local vendor at good rates, then more power to them… and for the rest of us who want to buy.
Please help keep this thread alive.
Great inputs PPtk!
I will point out that we are not talking about a high ratio boost driver though. This is one cell driving one emitter, with boost kicking in once the cell drops below Vf. Still not easy, but peak currents will not be as extreme as a high ratio boost.
In reality, I do believe the only way to do this will be a two-board solution (messy, costly), since the parts are probably not going to fit on one board. Even if some passives are moved to the battery side, the emitter side will be very crowded. This is the primary issue that Bill from Lightmalls had with the design. By reducing the drive to around 3.5A, it got a little better.
I believe that too. Even with a so23-8, 4x4mm qfn or similar sized microcontroller, there is just not enough room.
The power stuff will probably occupy one board, and the µC will need a second one. I guess this is still going to be cheaper than making a real high density design. But we’ll know more when some actually working prototypes exist.
Cramping all that stuff into an 17mm pill cavity will still be somewhat of a challenge (maybe .5 or .8mm pcb needed?). Looking forward to some experiments when I get the time. (I’m sick of studying for silly exams, still one moth to go. yay )
Given the height & component size restrictions does it still make sense to stick to the 17mm dia? Are there enough lights out there that have the necessary depth to fit such a driver, but can't take anything bigger than 17mm? I'm assuming most of these aren't going to be used in P60 pills.
Would it be easier to design & commission a suitable compact 2S 18650 (side-by-side, but with a C8 size head) host instead (unless something similar already exists), and use a buck driver? That would still be reasonably compact, it's the length of inline 2 cell lights that makes them awkward.
Hi,
Sorry to jump in, but I have a couple of thoughts… feel free to ignore :)…
- I think that one of the things you all should think on/focus on is “form factor”, in addition to the electrical/electronic design. What I mean is that you all also have a lot of experience trying to jam in a driver, whethere single-PCB or multi-PCB, into existing pill spaces, so, think about “If this driver was such-and-such size, it would sure be a heck of lot easier to get it into this darn pill arrangement.”
- Also, think about partitioning functionality? Maybe have a single PCB that has the electronics for driving the emitter and a 2nd PCB that hosts the “smarts” (MCU, etc.), but also such that the 1st PCB could, via some jumper settings, function as a standalone single mode booster? So, if you have a pill with limited space, you could use just the 1st PCB by itself for a single-mode light, but if you have a more spacious pill, you could use both PCBs and get multi-mode.
Again, just some thoughts…
Jim
Is there really no such thing readily available?
In that voltage/current range, one could use anything from a dedicated synchronous buck LED driver to a quick&dirty comparator based switcher. There is no parts gap like in the single cell 3A+ buck/boost application.
Strange no one builds such a thing.
@ohaya
Of course functionality is an important design aspect. There is no use in building something no one wants to have in the end.
Those things always need to stay in the mind, and Ideas should be documented here so they don’t get forgotten.
There may be, but not one I'm aware of. I haven't been at this nearly as long as some of you guys but I think if there were such a light/host, I would have seen it being raved about here by now. I've seen stuff like ZY-T08 modded to convert from 2P to 2S but that's got way too big a head for something that would compete with single cell lights, like I said around the C8's overall size just with a wider battery tube.
The initial primary intent is still to produce a driver that will fit the widest range of flashlights possible while adequately driving an emitter @ +3A. This is why we chose the 17mm size. We also want it to be mass produced in large quantity to drive down production costs and make it more affordable for everyone. Just a guess, but probably as much as 20% of all production might possibly go to the P60 crowd… if it could be made small enough to fit. We really do want to please everyone.
Now with the constraints of fitting everything on a single board, a stacked design is being discussed, but we are still hopeful of making it fit within the 17mm width. While this would preclude fitment into smaller pills (P60 and the like), it would still be extremely useful for most single cell flashlight builds.
I have more than a few budget flashlights (C8 and similar) that use 20-21mm drivers, but they are not the norm in this price category of flashlights. In budget lights, most of the the descent quality and popular/recommended examples still contain a 17mm driver. Any size other than 17mm would probably eliminate 80% of the lights we might want to mod with this driver.
Remember, we want this to be useful and available to as many people as possible to help promote the hobby and drive down costs.
If anyone ever makes it to the design stage, if possible please consider:
- MCU placement to be user accessible for programming
- Resistor placement accessibility for swapping for different current outputs