You guys are going to like this post a lot.
Doing voltage measurements from L2D-CE
Not testing turbo, probably not safe (I'm using a 3A 18V adj PSU)
Might blow the head anyway though, we'll see. *BOOM HEADSHOT*
Preliminary results:
L1D users (or L2D users like me who use an aluminum foil "battery") should be interested in the <1.5V results!
Methodology:
1. Constant voltage, variable current. Current limit set to 2.1A. (See note 2).
2. Note that these are not battery measurements, these represent infinitely awesome batteries with no internal resistance.
Bold entries show out-of-regulation behavior.
Non-bold entries are in "High Efficiency Mode" [HEM].
Observations:
1. High mode goes out of regulation at 1.3V, and
begins to squeal audibly as well as
go crazy on the power consumption. Medium mode goes out of regulation around 1V, and begins to go
crazy on power consumption, but doesn't squeal. Low mode does
not go out of regulation at all, but instead,
the flashlight refuses to turn on below about 800mV.
2. The Vf of the LED at 350mA (assuming high = 350mA) is around 3.5V. I suspect it's actually lower, but Fenix's circuit probably 'inflates' this measurement of the LED 350mA Vf to be higher because if it were 3.3 as the Cree datasheets say it should be, we'd have problems driving the LED at low with fresh Alkalines (1.5+1.5 @ 60mA is quite plausible).
Note 1: I didn't measure Turbo mode, but... at 1V, it drew over 2.1A before I realized I was probably cooking the circuitry!
Note 2: I found out that the circuit may need to draw over 1.3A when switching modes at low voltage. If you don't feed it enough, it'll remain stuck in low-efficiency mode, explained below.
I observed this when testing at 0.9V. The flashlight drew 1.3A (the current limit!) and depressed the PSU's voltage output to 400mV! This yields... 520mW, which is incidentally the same power consumption of medium!! But it was not as bright as medium, apparently because it's also much less efficient!)
Circuit behavior:
The circuit requires 800mV to
start; no "run-down" test was done to determine
shut-off voltage. (These are different; you can run a L2D-CE down enough that you can then turn it off, but not turn it back on again; the LED would be dimly lit for this to happen)
The circuit proceeds to bootstrap in
"Low Efficiency Mode" to hit a target output current, and will draw
incredible amounts of current to do so; the flashlight may even
SQUEAL!! Once it reaches the target output, it will go into
"High Efficiency Mode" and reduce power consumption while staying in regulation.
So what happens when I have my flashlight set to "High"? (Note that old, used 1.3V alkalines are probably below 0.8V/cell at 700mA)
1) 2.7V to 1.5V: the circuit goes into HEM, I have High mode etc. and I'm happy.
2) 1.4V to failure: the circuit goes out of regulation. LEM kicks in as the circuit tries to regain regulation. The batteries are drained at incredible currents (see note 2), and if the batteries can keep up, the light remains as bright as it was in HEM. But that is sadly not ever going to be the case, so output drops from "high" to "medium" for me, while consuming a lot more power than HEM-medium.
Going to do 1.5, 2.0, 2.6, 3, and 3.6V measurements.