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Thread: "resistive" mode regulation

  1. #1

    Default "resistive" mode regulation

    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

    Battery Voltage (V) Mode Current (mA)
    1.25 Low/med 3.7 / 82
    1.45 low/med 4.7 / 106
    1.58 low/med 5.5 / 126

    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.

  2. #2
    Flashaholic* Timothybil's Avatar
    Join Date
    Nov 2007
    The great state of Iowa

    Default Re: "resistive" mode regulation

    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.
    You don't need a parachute to skydive. You DO need a parachute to skydive twice.

  3. #3

    Default Re: "resistive" mode regulation

    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.

  4. #4
    Flashaholic* hiuintahs's Avatar
    Join Date
    Sep 2006

    Default Re: "resistive" mode regulation

    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.

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