Post by thread:[EE] trouble while driving power leds (OT topic ha

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)

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) -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.375 / Virus Database: 268.0.0/267 - Release Date: 22/02/2006 part 2 35 bytes content-type:text/plain; charset="us-ascii" (decoded 7bit)

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?

{Quote hidden}> 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? 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 -- FCC Rules Updated Daily at http://www.hallikainen.com