"resistive" mode regulation

[sbslider]

I use the word regulation loosely in the thread title. I have a Manker E01 I use as a night stand light for using in a dark house. I confirmed something I suspected for some time, that is that the light output on the the lowest two modes is proportional to the battery voltage. I don't really use the high mode, so I have not examined the performance there. On the lowest two modes the current drawn from the battery is proportional o the battery voltage. Brief chart below

[TABLE="class: grid, width: 500, align: center"]
[TR]
[TD]Battery Voltage (V)[/TD]
[TD]Mode[/TD]
[TD]Current (mA)[/TD]
[/TR]
[TR]
[TD]1.25[/TD]
[TD]Low/med[/TD]
[TD] 3.7 / 82[/TD]
[/TR]
[TR]
[TD]1.45[/TD]
[TD]low/med[/TD]
[TD] 4.7 / 106[/TD]
[/TR]
[TR]
[TD]1.58[/TD]
[TD]low/med[/TD]
[TD] 5.5 / 126[/TD]
[/TR]
[/TABLE]

As far as I can tell it does not use a form of PWM for regulation, at least not one I can see. I suppose if the frequency was high enough maybe I would not see it. Anyway I am just curious if anyone has an idea of how the light sets up the three modes.

 

[Timothybil]

First, there is a driver in your light, I am assuming a boost one to get the 1.5v from the cell up to the Vf of the LED. It appears from your testing that it is not a constant current one, but just a fixed amount of boost. That would fit into your data since it follows the I=V/R equation. So a decrease in voltage will result in a decrease in current since the R, that is the load, is remaining constant. I am also assuming that the different modes are achieved by differing the amount of the fixed boost.

As I said, these are all assumptions based on my small knowledge of electronics, esp. those of drivers. I am open to being corrected by anyone whose knowledge of these matters exceeds my own.

 

[sbslider]

Yes, I agree the voltage needs to be boosted up to drive the LED. I am not sure how sharp the slope of the I vs V curve is for this emitter, which is a Nichia 219b I believe. I also meant to mention the current in low mode with the 1.58V battery is tracking with what I see going to another "moonlight" mode light I have, Thrunite Archer 1A V3 which also puts out 0.1 lumens in its lowest mode, and draws about 5.x mA, depending on battery voltage. For that light I see the current increase as the battery decreases, so I can tell there is actual regulation going on there.

 

[hiuintahs]

I think Timothybil is correct in his assessment of what is going on. It has to boost the voltage up but its not as sophisticated as a regulated light otherwise as you said, the battery current would go up as the voltage goes down. I think there are a number of drivers that are not necessarily current regulated..........ones that are trying to be as simple as possible. The Zetex ZXSC300 (or 310) comes to mind. With a cap across the output, you see no pwm, but at the expense of a little efficiency loss. This was the driver that Terralux used in the 2AA Mag light upgrade module years ago. Not sure if they still do or not.