If you’re asking about BST21, which is the single sided boost driver with 21mm component clearance, it can fit in probably many lights, for example the WT1M/WT3M (25.5mm), D4S (31.2mm),DM11, KR1, PL09, some Convoys 21700 with large drivers M21D (26mm IIRC), MT01/MT04 and Astrolux equivalant, probably a number of sorfin and Astrolux 21700 lights.
But as you can see they have different driver diameters, which would mean different production batches, or maybe one larger diameter could be produced ( or 2) then people would file them down to the suitable diameter for their light, but are people willing to do that ?
Assembling and testing the MP3432+MP2145 NiMH-li-ion boost+buck driver :
The MP3432 was used specifically (instead of MP3431) because it has a passthrough mode, meaning it stops boosting when the input voltage is higher that the output voltage and behave like a piece of wire, with some resistance (high side FET+ boost inductor = 10mΩ+8.2mΩ), this output voltage being the boosted voltage, not the LED voltage, presently the boosted voltage is set at 3.37V, then this serves as the input voltage for the constant current buck driver.
If you look at Vout at 3Vin and 4Aout, it’s lower than at 4Vin, that’s because the 3.37V boosted voltage is not high enough to allow 4Aout at ~3.28Vout, which is the LED Vf + drop across the longish wires and current shunt, used for accurate current measurement. It could only do ~1.7A.
So I used a lower resistance shunt there, lowering the output votage needed for 4A. A 519A at 4A has a Vf around 3.2V, so it should be OK, if a higher Vf LED is used then the boosted voltage should be set a bit higher to allow full output at any (li-ion) Vin.
I was a bit worried about the passthrough mode because it only works in PSM, meaning the switching frequency decreases in the audible range at very low output and could generate noise, like my first driver with the TPS61288 did, but I hear nothing so that’s great. Plus now the power consumption will be lower at very low output vs USM (ultrasonic mode, freq>30kHz).
Considering I used 4020 inductors (4x4x2mm) the efficiency is really good. Though the fact that it peaks at relatively high output current means that I might have used a too small inductance (680nH, 8.2mΩ) for the boost converter. It would be good to test with XGL4025 (4x4x2.5mm), like 900nH (7.4mΩ), or 1uH (8.5mΩ), it could maybe break the 90% barrier with NimH voltages.
Another great-looking design. Thank you for sharing, especially the test data. Really great performance even on an NiMH cell - 6W with a fresh cell and close to 5W even as it nears empty.
I had to read back through the thread a couple pages to remind myself of the previous FWAA mods. If I understand right:
The latest FWAA driver is the cascaded boost-buck design. This one works on both AA and 14500, where as the previous version had an issue with the boost chip unexpectedly not working at low voltages.
The first FWAA mod thefreeman did used a boost only driver, so it was matched to a triple MCPCB that was modified to feed the three LED’s in series (~9V) instead of parallel (~3V).
Both designs are very similar in efficiency, with seemingly a slight advantage in certain conditions in efficiency for the boost-only driver, and more obvious advantage in maximum power, but of course, the cascaded boost-buck offers the most flexibility (suitable for both the FWAA and FW1AA, for example).
And the latest here boost+buck with MP3432+MP2145, the MP3432 being larger and requiring more passives I had to use 0402 ones, but it has lower resistance FETs (6/10mΩ), so it’s more efficient/powerful in the end.
Once I receive XGL4025 inductors I’ll make new measurements, maybe push it to 5 or 6A on li-ion and a bit more on NiMH as well.
Another way to increase the efficiency a bit would be to use the TPS62867 for the buck converter, which is a bit better than the MP2145, but aside for availability problems, the layouting coupled with the MP3432 is kind of difficult, while the IN/OUT/GND pins of the MP3432 and MP2145 conveniently match.
So I’ve been working on making it production ready :
now single sided for lower assembly setup fee, the FWxA having 20mm clearance I used BST21 as base, a 6024 inductor instead of 7030 and a few 0402 passives to shrink it to 20mm
for the different output variants (6V5A, 9V3.33A, 12V2.5A) I left the resistors to be changed as 0603 for easier swapping.
I used a much less costly inductor that still has very good characteristics, only very slightly higher DCR (8-9.6mΩ instead of 6.8-8mΩ for XGL6020)
Well aside from size constraints, the magnetic switch requires additional hardware, and the firmware would have to be adapted for it (unless it simulate a simple on/off momentary switch)
They’re easier to work with than fat, springy and stranded silicone wires in my opinion. They virtually take no space, they’re rigid so you can bend them as you see fit and they stay put, no need to remove the insulation (it melts at high temp)
Ah. Insulation that does not require stripping … I did not know. All I have encountered are the silicone and teflon types. Is what you have enamel, like the magnet wire I used a lifetime ago?
