I’m curious about something?
On the other thread about the Cofly light which appears to use the same driver, nofearek9 reported 1.4 amps at the tailcap with 2xLi-ion. So I guess that’d be like 1.4 x 8V = 11.2 watts, right?
On the emitter side, let’s say the Vf was about 4V, so if the power-out was ~11.2 watts, then emitter current should be about 2.8 amps?
But, from the testing I did initially with the bench power supply, even though I didn’t go more than say 5.5V, current at the emitter didn’t increase to that level (seemed to go down instead)?
Shouldn’t I have seen, say, 3 amps at the emitter?
I’ll need to test with the single XM-L again, but this time, bump the Vin to the driver to maybe 8V (yes, I’m willing to lose that emitter)…
EDIT: I just tested again, both with a single XM-L U2 (I think) and a new XM-L2, and am seeing the same behavior I saw before. With Vin up to 8V, the current both at Iin and Iemitter were dropping to about 0.7 - 0.8 amps. I also measured Vemitter (just in case) and was about 3V with the XM-L2 (I didn’t make a note of it for the XM-L, but I think that Vemitter was about the same, i.e., about 3V).
So I’m still puzzled!
I understand this is a buck driver, but where the heck is that power/watts disappearing to? Is the driver soaking up all the extra power/current?
I SHOULD be seeing about 2+ amps Iemitter, correct :(?
EDIT:
Although this is not the right chip, just to get an idea, I found this:
http://andrewpearson.org/?p=643
So, assuming that this driver is using a similar chip, I am guessing that the answer to my question about where the excess power is going is to the sense resistors in the R1/R2 voltage divider (fig. 11 in the above page), and probably the reason I’m seeing lower than 3 amps is that the sense resistors’ values are controlling that.
So that’s why you all are looking for the board without the toroid, to try to figure out which resistors could be/need to be changed to try to bump the driver output current?