On high or lower modes? The Convoy and similar drivers have an odd quirk that causes poor regulation on lower modes.
I built my first Convoy recently using an 8x7135 Qlite driver - pretty similar to the Convoy driver, but I have STAR firmware on mine. Out of curiosity, I tested the regulation with a linear power supply. Mine held regulation at ~3 Amps until the input level dropped below 3.4V when driving a 2.8-2.9V rated 219C. It dropped to 50% of initial current draw at 3.15V.
Considering Nichiaās datasheet shows the forward voltage is 3.4V at roughly that current level, this $5 driver seemed to have perfect regulation. There are caveats for voltage binning and the temperature dependence of Vf, but they donāt change the conclusion much.
Surprisingly, regulation was far worse on lower modes.
My 750 mA target (25%) mode fell out of regulation at 3.9V.
My 90 mA target (3%) mode was already out of regulation at 4.3V.
This wasnāt actually a surprise to me. I was looking for it specifically because when shopping for a driver, I noticed HKJ documented it over 4 years ago. He speculated based on oscilloscope data that the 7135 chips respond too slowly to the 16 kHz PWM to turn on fully when the duty cycle is low. Maukka measured similar when he did a more cursory output test of an S2+.
However, the D4 also uses a high frequency PWM for its 7135 chip, yet does not share this issue. I donāt know if it is due to the specific brand of 7135 used, a driver design issue, or if Toykeeper, TomE or others know a firmware trick to avoid it.
All of the above. The FW3A uses a few methods to avoid that problem:
Chip brand: āRaptor clawā 7135 chip chosen specifically for its activation speed, so it will perform well with short pulses. The low-mode problems are mostly seen on āfailboatā 7135 chips.
Driver design: 1x7135 chip on its own channel, so it uses the 350mA Vf instead of the 3A Vf, and can thus regulate longer.
Firmware: Slower PWM frequency at the lowest levels, like moon, to improve stability and reduce voltage sensitivity. Also reduces total power draw significantly, so moon runs about 3X longer than it would at full speed. (the D4 doesnāt do this, but the FW3A does)
Soā¦ regulation on this thing actually works pretty well.
You probably donāt need to read every post, but ToyKeeper is one of the main FW3A team members who actually posts updares on this project. Itās always good to read her posts, even if the techno stuff goes over your head. Lol
FW3A Team
Fritz15: Design
Tommy TLF: General TLF communication
DEL: Driver Tom E: Firmware (originally), driver
ToyKeeper: Firmware / UI, BLF gardening The Miller: General BLF communication
pepinfaxera: Interest list management
MRsDNF: Early prototyping
Neal: Facilitating tasks in China
Lumintop: Manufacturing
1233 - # Post . bansuri
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Correcting: ā¦
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Apologies, Iām sorry.
I need to edit list.
Greetings.
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Totally agree. This summer, I replaced my BLF A6 cycling light with a Zebralight SC600w MkIV Plus. The BLF A6 uses a FET+1 driver with a XP-L, and the Zebralight a boost driver with an XHP50.2. I like to use about 700 lumens when cycling, and the BLF A6 would give me about 1 hour of output before it dims too much to be useful to me. The Zebralight gives me a constant 700 lumens for almost 3 hours, until the battery is drained to 2.8v. (Both using a Sanyo GA cell.)
While I like the BLF A6 as a casual light, there are some circumstances where FET will not do, and even a 8x7135 like a Convoy wonāt do either. When run-time and constant output is required, you gotta go boost or buck/boost.
I wonder if thereās a way in firmware to increase the PWM duty cycle of a FET driver as the battery voltage drops? It wouldnāt help with efficiency, but it would help to regulate output much better (on levels below max).
This is one of the differences between a $20 light and a $100 light. Some folks might prefer the A6 along with extra batteries for well less than half the cost. Good arguments can be made for both lights.
Luckily things get better as time goes on. We are close to getting high powered (40+ watt) aftermarket boost drivers with sweet UIās like NarsilM and Anduril. Maybe in a few more months?
At the present time we only have medium powered drivers (20W) with a set - low, med, high, turbo and dbl clk for strobe - user interface. :confounded:
Maybe the next BLF light can use a boost driver. :+1:
I could be wrong, but Iāve got a feeling it could be a significant price difference for a good boost driver compared to a FET +1 driver, in terms of Chinese production cost.