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Thread: PWM or linear?

  1. #1
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    PWM or linear?

    I have built a helmet light with 3 XM-L and I use a PowerLine Constant Current Power Supply (2800mA) from led-tech.de

    My question is what's the difference between using a driver with linear regulator from using a driver with PWM capabilities?

    Can someone recommend a driver that generates the maximum 3A for this application? Just a simple driver, not a advanced driver like the H6Flex.
    Maybe three 1A driver in parallel http://www.led-tech.de/en/LED-Contro...3_118_119.html ?

    I just want the maximum lumen out of the XM-L's, but I'm very satisfied with the helmet light so far. I can recommend using the LM1 lens for MC-E.

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    Have you looked at lFlex? It's cheaper than 3x 1A drivers from led-tech, and has many more goodies. It drives 1 XML from 1 LiIon/LiPoly.

  3. #3
    help with the zip please
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    Quote Originally Posted by Toaster79
    Have you looked at lFlex? It's cheaper than 3x 1A drivers from led-tech, and has many more goodies. It drives 1 XML from 1 LiIon/LiPoly.
    bit I don't believe it will drive 3 xm L.

    Hoobs first off I don't think your eyes will actually pick up the difference between the output at 3A and that at 2.8A. Happy to stand corrected but I think with three @ 2.8A you've already got so much light that the small percentage increase will be negligible, vertainly not worth the expense of changing drivers.

    Secondly, how do you find the Powerline? How are you dimming it? I have been looking at their range of drivers for ages but have always been put off because I've never found an easy way to dim them that is suitable for a helmet light.

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    ..2,8A to 3A ?
    you wouldn`t notice any difference!
    tell me what the gain would be
    how hot does your unit get at 2.8A
    ...Scun.thorpe, UK

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    Quote Originally Posted by emu26
    bit I don't believe it will drive 3 xm L.

    Hoobs first off I don't think your eyes will actually pick up the difference between the output at 3A and that at 2.8A. Happy to stand corrected but I think with three @ 2.8A you've already got so much light that the small percentage increase will be negligible, vertainly not worth the expense of changing drivers.

    Secondly, how do you find the Powerline? How are you dimming it? I have been looking at their range of drivers for ages but have always been put off because I've never found an easy way to dim them that is suitable for a helmet light.
    Dim it? Why?

  6. #6
    help with the zip please
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    Quote Originally Posted by hoobs
    Dim it? Why?
    I assume you're joking, or a complete novice?

    I have never gone night riding when I have needed high the whole time, and that is with lights that have an output far less than three xml @ 2.8A.

    When that output comes at the cost of having to carry bigger batteries or go for a shorter ride then I'll choose to dim my lights.

    do you do shuttle DH runs by any chance? I get it if that's the case, but if it were I'd just build a quad xml for the bars as well as the triple on the lid 'cause the weight doesn't matter...much

    Edit: I see in your sig that your bike is a Yamaha 250WRF. are we talking mountainbike riding or motorbike riding?

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    Hoobs

    any chance of some photos of your triple xml light so we can see how you have it mounted on the helmet and how it copes with the heat a triple set up can generate.

    I agree with the others who say you will not see a difference from 2.8 amps to 3 amps
    better to add another led to the mix if you need some more light .

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    I have always found more led's to work well. Now if you were overdriving a lot, like running your light at 4A rather than 2.8A, you would see a difference. Then the devil steps in; you are required to use a larger heat sink. I use 21 sg in of heatsink (with short fins, not RBF; sigh) with 27 watts of input power. I figure a couple watts in the regulator, rest in the led's. This light runs cool in the cold weather, warm in the hot weather. Post a few pics.

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    Yes, I ride motorbike, Swedish enduro.
    And my goal with this project is to beat my 35W xenon light that I now have as a helmet light.
    I want a quite wide beam and a lot of lumen, all the time, so no dimming.

    So I'm not joking but I'm a complete novice in building LED lights.

    I just need to decide the right configuration (no of XM-L, optics)
    I have a 12V system.

    6 XM-L at 1400mA (units of 2 XM-L in parallel, 3 units in series)
    3 XM-L at 2800mA (in series)

    Is it better to have more LEDs at lower Amp than having fewer at maximum Amp?

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    OK for a motor bike helmet. I would favour making. 2. double. or triple. XMLs
    using H6flexs one in each. and fitting them one on each side of the helmet for balance

    you say you want a wide floody beam. so the triple and cute optic. will give you a terrific amount of light. will need good heat disipation for when you are not moving if you dont dim them.

    going for two lights. means smaller housings and a fail safe if one gets struck by a branch or something.

  11. #11
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    Quote Originally Posted by hoobs
    Is it better to have more LEDs at lower Amp than having fewer at maximum Amp?
    Yes, by all means. First, you will burn a bit less power (as Vf of the leds will be lower) and second, you will get a bit more lumens with twice the number of leds at half the current - for XM-L this difference will be about 20%, according to the Cree's data sheet.

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    Does Lumen adds?
    I mean if I have two leds that generates 100 lumen each is the same as one led that generate 200 lumen?

  13. #13
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    Yes.

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    Why not build a led driver with a LM150 http://www.national.com/ds/LM/LM150.pdf

    Just a simple 3A current regulator.

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    Quote Originally Posted by hoobs
    Why not build a led driver with a LM150 http://www.national.com/ds/LM/LM150.pdf

    Just a simple 3A current regulator.
    It has huge dropout voltage. At 3A the dropout voltage is ~2.2V, so you are burning 6.6W!

    Arne

  16. #16
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    Quote Originally Posted by arnea
    It has huge dropout voltage. At 3A the dropout voltage is ~2.2V, so you are burning 6.6W!
    Likely that the power consumption is of little importance to hoobs as he is using his light on a motorcycle. Maybe his concern should be that it would add significantly to the heat load in a housing.

  17. #17
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    I have now built a constant current regulator with a LM338.
    I connected my three XM-L's to it and lighted it up, I measured the current to 3.06A and the voltage across the three XM-L's to 9,4V.

    Isn't 9,4V a little bit low Vf? I expected about 10V.
    The input to the regulator was 13V, 5A.

    But what a light!
    Tomorrow evening I will take it out in the dark forest to compare it to my xenon light.
    I'm pretty sure that the xenon will lose this fight.

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