My buddy has bought two Convoy L21A lights, one with an SFT40 and one with an SST40. He wants me to put a W2 in the the one that has an SST40 and try to match amp draw on the two lights so he can compare the difference between the two throwy emitters.
Now, I’ve been out of the modding scene and things have been changing… so I’m seeing very different drivers in these two lights!
The silver SFT40 driver looks to be regulated? It’s making 6.95A at the tail off a 40T.
The black SST40 has two FET’s and is making 5.9A at the tail. It’s tempting to remove those two FET’s in favor of an Infineon and bypassing the R020 sense resistor to push a W2 in direct drive. Should I?
As far as the Inductor equipped driver, yeah, don’t remember much about what can be done there.
Yeah, there’s numerous lights that run on a single cell that have buck drivers. Off the top of my head: ZL SC64c LE, Lume1, Skilhunt H04/M200, Sofirn SP35, Convoy 8A (used in many of his lights, S21D, etc.)
As @quahog said the first one is a 8A buck driver, second is a linear driver.
For the buck driver the output (LED) current is not the same as the input (cell) current, the input current is lower as long as the driver isn’t in dropout (Vin close to Vout). the buck driver might barely be able to do 8A with an SFT-40 or CULPM1 and full cell due to the duty cycle limit of ~90% (Vout <Vin*0.9) of the buck IC used and higher component resistance.
For the linear driver Iin=Iout the the current can be measured at the tail, if you get 5.9A then it must be a 6A driver.
15Ω ? 15mΩ ? 15mΩ||20mΩ=8.6mΩ
for 8A newRsense = 5.9*20/8 = 14.75mΩ
But again the actual current depends if it’s in dropout or not, reducing the circuit resistance by bypassing spring is a good idea to reduce the dropout voltage, not sure replacing the double FET will change much though, unfortunately the sense voltage used on this driver is high : -5.9*20= 118mV, so that’s 0.12V wasted here, reducing the sense voltage is possible but the resistor to change is more difficult to identify.
Ok, now I really just don’t get what’s going on here. On the linear driver, the one with an R020 sense resistor… I removed the 15 Ohm resistor and stacked an R025 sense resistor. And it changed… nothing! Still 5.93A at the tail.
Controlling current was never my thing, sense resistors are not something I have a lot of. I do have quite a few drivers removed from lights, some of which have these, usually in higher values. The R025 was the lowest easily obtainable, there is an R010 but at this point…
Ok, so… the linear driver didn’t like the sense resistor pads bridged, 3 of 5 modes were all Turbo.
I removed the bridge and stacked the R025 with the R010 for 5.793 mOhms and this works. 5 separate modes with Turbo at 8.71A on a 48G cell, for 1320 lumens from the Osram W2 emitter. (30x30 package)
