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'[EE] trouble while driving power leds (OT topic ha'
2006\02\23@093041 by Gökhan SEVER

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Greetings to Piclist community,

i'm new to power-led design area. I have to design a led strip with 6 white
power led. I chose Luxeon
III Emitter White leds for my application. I have prepared the pcb and
proper heatsink for my design.
The strip will be sourced with 24V DC Meanwell smps. (this smps has max 10A
drive capability) So i
calculated required resistor value for driving the strip at 1A which is
24-6Vf = R (The datasheet of
Lux III Emtter notes that it has 3.90 forward voltage at 1A) So i have
chosen the Resistor value
0,75R / 5W. But when i conntected the serie to the power supply i only get
500mA and the value
increased slowly to the 650mA and after that no increasing in current.

I looked the luxeon datasheets and application notes over and over but still
i havent found where is
the problem? Do i need to design a specific smps with different topologies
or else?
(Datasheets and application notes can easily found on http://www.luxeon.com)

2006\02\23@130318 by Roy

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face
part 1 1882 bytes content-type:text/plain; (decoded 7bit)

Are your LED in series or parallel?

I would normally put one resistor in series with each LED with the LEDs
in parallel to the supply.


+24v DC  ------------------
             \           \
             /           /
             \           \
             /           /
             |           |
             |           |
            ___         ___
            \ /         \ /
             v           v
            ___         ___
             |           |
             |           |
0v DC    ------------------            

_______________________________________

Roy Hopkins
New Zealand
_______________________________________

>
> i'm new to power-led design area. I have to design a led strip with 6
> white
> power led. I chose Luxeon
> III Emitter White leds for my application. I have prepared the pcb and
> proper heatsink for my design.
> The strip will be sourced with 24V DC Meanwell smps. (this smps has
max
> 10A
> drive capability) So i
> calculated required resistor value for driving the strip at 1A which
is
> 24-6Vf = R (The datasheet of
> Lux III Emtter notes that it has 3.90 forward voltage at 1A) So i have
> chosen the Resistor value
> 0,75R / 5W. But when i conntected the serie to the power supply i only
get
> 500mA and the value
> increased slowly to the 650mA and after that no increasing in current.
>
> I looked the luxeon datasheets and application notes over and over but
> still
> i havent found where is
> the problem? Do i need to design a specific smps with different
topologies
> or else?
> (Datasheets and application notes can easily found on http://www.luxeon.com)

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part 2 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\02\24@035235 by Gökhan SEVER

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Another concern about luxeon power leds:

Why does the typical lumens value given at [W] unit rather than [lm] unit
for royal blue leds?

The datasheets note that "Royal Blue product is binned by radiometric power
and peak wavelength rather than photometric lumens and dominant wavelength."
(the state has been given but no description.)

Also i read an article named "More Light - Practical high-power LEDs" from
Elektor Magazine. There says: "The royal blue version emits light with a
wavelength of 450nm and the eye is so insensitive to this colour that the
luminous flux is given in miliwatts. This parameter gives some indication of
the LED efficiency; 10% of the 1W of electrical power is converted to
visible light."

What is the real explanation of this case?

2006\02\24@114027 by Harold Hallikainen

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{Quote hidden}

As I recall, Lumens refer to an apparent brightness to a human observer.
The watts per square meter "power density" at various wavelengths is run
through a photopic filter to attenuate wavelengths the eye responds poorly
to so the lumen value approximates what an observer would say the
brightness of the lamp is. I wrote some PIC code to do this, taking values
from a spectrometer, multiplying by the photopic filter values for that
wavelength, then adding the results.

The power output (in watts) ignores the brightness as preceived by the eye
and, instead, just considers all power equally. The royal blue LED is
often used for purposes other than "lighting" (where someone looks at the
light). I used it in a dental curing light where the light activates
curing components of the composite. The light characteristic we're
interested in this application is watts per square meter (they use
milliwatts per square centimeter, but I think metric should use the basic
units with just a single scaling prefix!) at the appropriate wavelength.

Harold



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