PowerPeg thermal management and efficiency - Page 1
Forum section: electronics / projects

author: TEMProducts
author_rank: Newbie
timestamp: August 11, 2015, 05:52:42 pm
content: Everyone loves the Cree XML. This past week I did some long overdue applications testing based on the Cree XML with PowerPeg thermal management.http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Discrete-Directional/XLamp-XML2About Cree XML LEDOver the past four years the Cree XML series LED has been my favorite LED. It is a very popular component in DIY projects and commercial products around the world.Cree XML series is one of many new-generation light emitting diodes which are designed to be surface-mounted on a PCB. This small LED packs big power into a package only 5mm X 5mm in size.The thing that makes the XML so special is it’s especially large die. The semiconductor inside the XML is 3mm X 3mm in size, providing nine square millimeters for light emission. In LED physics size does matter. You may be able to pipe more power into a smaller LED, but efficiency will undoubtedly be lower when emission area is limited.The 3mm die in XML LEDs is connected to a large thermal pad on the bottom side of the chip. The LED itself is rated at 10 watts maximum, but this rating is very limited by how effectively heat can dissipate from the LED.Efficiency in lightingEfficiency in lighting systems is important. As greenhouse gasses are continuously accumulating in the earth’s atmosphere, all the big names in lighting seek to produce the world’s most efficient light bulbs. LEDs aregreenbecause they use less electricity, and they are also green because they last for more years than old technologies.The especially large die in the Cree XML means it can:A) handle huge power for it’s size. Many of the new ULTRABRIGHT flashlights use the XML technology because it is just so powerful! The LED can be driven at up to 3 Amps if cooled properly.OrB) The XML can be driven at a moderate power level to achieve high energy efficiency!Ultimately the energy savings equates to less fossil fuel consumption, and a healthier planet.CalculationsCalculating the energy efficiency of an LED light can be tricky. In resistive circuits P = VI, but LEDs are semiconductors which means V is a function of the temperature and other variables.The best way to characterize the efficiency of an LED light is by conducting a lab test.The goal of this experiment is to test Cree XML LED at various power levels, and with multiple heatsinks. The effect of each heatsink on energy efficiency will be observed.The HeatsinksAfter four years of research and development into PowerPeg Thermal Management, I have a beautiful assortment of standardized heatsinks to test.Once PowerPeg is soldered to the LED, any of these heatsinks can be added or removed.The ExperimentThe experiment is designed to monitor:the temperature of the thermal padthe forward voltage of the LEDthe light output of the LEDA benchtop power supply maintains constant-current through the LED during each test. Four heatsink arrangements were tested:PowerPeg with no heatsink attachedGP-43-A heatsinkGP-43-A-FC1 forced convection coolerWC-43-A water coolerThe experiment was repeated at three power levels (350mA, 700mA, 1500mA) for a total of twelve trials.The ApparatusAn Arduino Mega served as the controller. The KCA-259 thermocouple shield easily attached to the Arduino for temperature measurements.The LED was installed on a PCB with a TCAP-4325 PowerPeg.Tiny 40 AWG thermocouple wires were sandwiched between the LED and PCB for measuring the temperature. I started by welding the thermocouple wires to the copper pad on the PCB using a capacitor, then covered the pad with solder, then reflowed the LED on top.Test leads were soldered to the PCB as close as possible to the LED for measuring the forward voltage.The LED was mounted at the top end of an optical tube approximately 3” long. The optics tube contained a series of light diffusers and filters. The filters were necessary in order to bring the light intensity down to a measureable level.The light intensity is measured at the bottom end of the tube by a TSL230 light intensity sensor. The bottom half of the assembly was positioned inside a cardboard box to block out ambient light.ResultsThe experiment produced a comprehensive data set.When the LED kicks on the temperature of the system rises until thermal equilibrium is reached. Each heatsink reaches a different temperature for a given power level.Temperature affects light output. The measured light intensity was identical at the start of each test. Light output decreased as temperature increased.The forward voltage of the LED decreased as temperature increased.The power supply delivers constant current despite changes in voltage. The decrease in forward voltage means that power input also decreased proportionally (P=VI).Coefficient of relative power input was calculated by dividing the forward voltage at each point by the initial voltage.Then efficiency was calculated by dividing relative Lux by the relative power input.The experiment showed that efficiency was significantly improved by incorporating a thermal management system.More Pictureshttps://plus.google.com/photos/105142970227332631428/albums/6180263645545718161PowerPeg Applications Test PDFhttp://www.tem-products.com/PowerPeg%20Application%20Test%20Cree%20XML.pdfHackaday 2015https://hackaday.io/project/6874-powerpeg-thermal-management-system