Today, the editor has compiled the information on the relationship between the life and temperature of the LED injection molding module to share with you.

Everything happens,Develops and The process of dying,

LED injection molding moduleis no exception, has a certain lifespan. EarlyLEDjust Gifts such as flashlights and table lamps are not used for a long time, and the life problem is not prominent. But now LEDhas Begin to be widely used in outdoor and indoor lighting, especially high-power LEDRoadlamp, its power is high, the heat is high, the working time is high long, the problem of longevity is very prominent. In the past, it was thought thatLED injection molding moduleLife must be 10The myth of 10,000 hours seems to have been completely shattered. So where is the problem?

If power and drive failures are not considered,LED injection molding moduleThe lifespan is represented by its light decay,That is, the brightness will become more and more darker and darker after a long time, until it finally goes out. Usually define attenuation30% time as its lifetime.

thenLED be predicted? There is no easy answer to this question, and it needs to start from the beginning.

1, LEDLuminous Decay

Most WhiteLED is made of blueLEDIt is obtained by irradiating yellow phosphor. Causes LEDlight decay The main reasons are two, one is Blu-rayLEDIts light decay, blue lightLEDthe light decay is much higher than red, yellow, green LEDbe fast. Also one is the light decay of phosphor powder, which is very seriously attenuated at high temperature. Various brands of LEDIts light decay is differentthe same. Usually the manufacturer of LED A set of standard light decay curves can be given. eg USCree< /span>The company's light decay curve is justAs shown1 .

As can be seen from the figure, LED injection molding moduleThe light decay is related to its junction temperature, the so-called junction temperature is the semiconductorPNjunction temperature,the higher the junction temperature, the earlier Light decay, that is, the shorter the life. As can be seen from the figure, if the junction temperature is 105degrees, brightness dropsto70% has a lifespan of only over 10,000 hours, 95degrees210,000 hours while the junction temperature dropped to75degrees, the life expectancy is< /span>5Wan Xiao span>,65degrees can be extended to 9 10,000 hours. Therefore, the key to prolonging the life is to reduce the junction temperature. However, these data only suitable forCree LED. Not suitable for other companies' LED. For exampleLumiledCompany's LuxeonK2Luminance Decay The curve is as shown 2.

When the junction temperature goes from115°C increased to135℃, will make the life span from 50,000hours reduced to 20,000hours. OtherCompanies The light decay curve should be available from the original factory.

2, how to extendLED injection molding moduleLifetime< /span>

It can be concluded from the figure that the key to prolonging its life is to reduce its junction temperature. The key to reducing the junction temperature is to have a good heat sink . Able to put LEDThe generated heat is dissipated.

Here we are not going to discuss how to design the radiator, but which radiator will dissipate heat.A relatively good question. In fact, this is a junction temperature measurement problem, if we can measure the junction temperature that any kind of heat sink can reach , then not only can compare the heat dissipation effect of various radiators, but also know what can be achieved after using this radiator TheLED injection moduleLifetime.

The junction temperature appears to be a temperature measurement problem, but the junction temperature to be measured is atLEDinside, never take a thermometeror thermocouple put inPNjunction to measure its temperature. Of course, its case temperature can still be measured with a thermocouple, and then based on the given thermal resistanceaccording to the given thermal resistanceRjc (to the shell), it can be calculated its junction temperature. But after installing the radiator, the problem complicated again. Because usually LEDis Soldered to the aluminum substrate, and the aluminum substrate is mounted on the radiator, if only can measure the temperature of the radiator shell, span>Then to calculate the junction temperature, it is necessary to know a lot of thermal resistance values. includesRjc span>(junction to shell)< /span>,Rcm(case to aluminum substrate, in fact, it should also include the thermal resistance of the film printing plate), Rms(aluminum substrate to heat sink),< span style="line-height:1.5;text-indent:2em;">Rsa(radiator to air), only one data Inaccuracy affects the accuracy of the test. Figure3 span>givesLED span>A schematic diagram of each thermal resistance to the heat sink. A lot of thermal resistance is incorporated, making its accuracy even more limited. That is, says, it is even less accurate to infer the junction temperature from the measured surface temperature of the heat sink.

Fortunately, there is an indirect way to measure temperature, and that is to measure voltage. So which voltage is the junction temperature related to? What about this relationship?

We first start with the voltammetry of the LED Features start.

3, LED< span style="line-height:1.5;text-indent:2em;">Temperature coefficient of volt-ampere characteristics

We know that LED is a semiconductor diode, It has a volt-ampere characteristic like all diodes, and like all semiconductor diodesthis volt-ampere characteristic has a temperature characteristic. Its characteristic is that when the temperature rises, the volt-ampere characteristic shifts to the left. Figure4Medium Out of LED Temperature characteristics of volt-ampere characteristics.

Assume that the LED is displayed with IoConstant current supply, at junction temperature is T1, The voltage is V1, And when the junction temperature rises to T2When the entirevolt-ampere characteristic is shifted to the left, the currentIoNo change, the voltage changes toV2. These two voltage differences are removed by temperature, and the temperature coefficient can be obtained asmV/oC means. For ordinary silicon diodes, this temperature coefficient is approximately-2mV/oC. But LEDmost It is not made of silicon material, so its temperature coefficient should be determined separately. Fortunately, each LED Most of the manufacturer's data sheets give its temperature coefficient. For example, for CreeCompany TheXLamp7090XR-E High powerLED, Its temperature coefficientis -4mV/oC. Larger than ordinary silicon diodes2 times. As for the US Preh's arrayLED(BXRA) gives more detailed data.