First the disclaimer. I posted most of this at the entry #33 from this post XHP-35 But thought it might be needed it’s own thread.
After reading the specs on this chip it look doable. Do we have any electrical engineers out there that could design a 17mm board for this. A single cell XHP35 running 1800 lumens in a P60 dropin would give throw much closer to the XM-L led as apposed to the MT-G2 and still be more efficient than either. This would also be the same for any single cell light, keeping them still in the EDC realm. I mod a lot of lights but I tend to destroy many in the process. It’s too complex for my skills. Anyone want to take up the challenge as I believe this type of driver would also give practicability too 9v MT-G2’s, 12v XHP-50’s and 70’s. I believe high drain 18650’s and 26650’s could carry the loads. Most of the lights I carry or sell to others are EDC size. Don’t get me wrong I love the 3-5 cell 9-18 led light as much as the other but it is probable not going with me for a walk at night.
I will be having a go at making a driver using this chip (I’ve ordered the parts and can prototype on a cnc router). I think the biggest challenge is the multiple small traces and the need for an inductor (which will be the largest component). Ti do have a reference board which is 15mm x 38mm but that looks like it can be trimmed down quite a bit. The board outputs 18W at either 5, 9 or 12V which sounds perfect… the challenge is getting it onto an area 1/2 what it uses currently and implementing some sort of mode control (MCU switching feedback path / resistance?).
Edit:
E-fuse can be removed which saves some space and a little resistance. Page 8 shows efficiency above 90-92% from 0.5-1.3A from 3-4.2V which would mean a 4 Amp draw from a 3.7V cell to deliver 1.05A at 12V… well within what most Japanese cells can deliver without hurting battery life.
Well, without doing any actual measurements yet, I roughly estimated that you could possibly remove half the space from that board. The remaining area, if it can be converted to a round board of the same area, would still require a 19mm disc. With the possibility of removing several things (but also adding stuff, such as attiny13) and maybe making the driver double-sided, you should be able to get it down to a 17mm or maybe even 15mm driver. Can you imagine installing this with a XHP-35 in a 18350-size light with a high-drain cell? Talk about shock factor!
Edit: I just now printed the picture of the reference board, took some rough measurements, and did some more calculations. It seems a 15mm board would not hold everything on one side. But again, taking some things off you don’t need (yet adding back stuff you do need, like attiny13) and making it double sided should work within a 15mm round footprint. Now, when ya gonna get this thing built? I’d like to buy a few of each: 15mm and 17mm size. :bigsmile:
Would this also be an appropriate driver for triple XPE2 or Rebel emitter lights?
(I’m still not sure how much I don’t know about driver electronics and emitter matching)
Should do. The chip will provide any voltage from 2.7 through to 13.2V at 18W output… only the feedback resistance values and inductor size needs to be changed.
I have been looking for an ic like this for a while and it seems to be the best ive seen for this application. It does present a few challenges though. If you look at the datasheet, especially where it has the thermal images you can see this thing generates alot of heat, even in open air. I dont think this is a good choice for 12 volt leds because of the massive amount of heat. The other problem is getting a small enough inductor that can handle 5 amps. You can increase the switch frequency to get a smaller sized inductor but the amperage drops off when you do that. Another thing is the chip is physically large. Double sided is a must. But i think im going to take a stab at this one. It wont be cheap though.
Looks like both of those who took on the challenge have been gone for a long time, not a good sign… I wouldn’t be surprised if they’re both in a mental recovery resort of some kind, this sort of stuff can easily overload the brain.
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