1. what is the LED junction temperature:
The basic structure of LED is a P-N junction of a semiconductor. The experiment points out that when the current flows through the LED element, the temperature of the P-N junction will rise. In strict sense, the temperature of the P-N junction region is defined as the junction temperature of LED. Usually, because the chip of the component has a very small size, we can regard the temperature of the LED chip as junction temperature. So the size of the 5730 bulb and the 2835 bulb is directly related to the heat dissipation of the lamp.
The harm of 2.led junction temperature:
(1) the increase of temperature will shorten the life of LED
The life span of LED is characterized by its decay of light, that is, the longer the time is, the lower the luminance is, until the final extinction. It is usually defined that the lifetime of LED luminous flux attenuation is 30%.
(2) high temperature will cause permanent damage to LED
LED is encapsulated more with silica gel. If the junction temperature exceeds the solid phase transition temperature (usually 125 C), the packaging material will change to the rubber and the thermal expansion coefficient rises suddenly, which leads to the opening and failure of the LED.
(3) the increase of temperature will reduce the luminous efficiency of LED
As the temperature increases, the radiation recombination probability of electrons and holes in the potential well decreases, resulting in non radiative recombination (generating heat), thereby reducing the internal quantum efficiency of LED a..
With the increase of B. temperature, the concentration of electrons and holes will increase, the forbidden band width will decrease, and the electron mobility will decrease.
C. with the increase of temperature, the quantum efficiency of phosphor is reduced, the light emission is reduced, and the external light extraction efficiency of LED is reduced.
The properties of D. silica gel are greatly influenced by ambient temperature. With the increase of temperature, the thermal stress inside silica gel increases, leading to a decrease in the refractive index of silica gel, thereby affecting LED.
3. light effect
In general, the effect of luminous flux decreases with the increase of junction temperature. That is to say, when the temperature reaches the initial temperature, the output flux of light will have a recovery growth. This is because some relevant parameters of the material will change with temperature, resulting in the change of LED device parameters and the output of LED. When the temperature is restored to the initial state, the change of LED device parameters will vanish and the LED output will return to the initial state value. For this reason, the luminous flux of LED has "cold lumen" and "hot lumen" points, which indicate the light output of LED node at room temperature and a certain temperature respectively. LED
4. The influence of temperature on the forward voltage of LED
The forward voltage is an important parameter to determine the performance of LED, and its size depends on the characteristics of the semiconductor material, the size of the chip, the formation of the device and the fabrication process of the electrode. When the current is fixed, the forward voltage of LED will decrease when the temperature rises. Because the relationship between forward voltage and temperature is nearly linear, most of the LED thermal resistance tester uses the characteristic of LED to measure its thermal resistance or junction temperature.
5. high temperature will limit the maximum injection current of LED
With the increase of temperature, the forbidden band width of material will decrease, and the maximum injection current will decrease. Temperature also affects the distribution curve, color temperature and color rendering of LED. The influence of temperature on refractive index of light transmittance will change the spatial distribution of LED light emission, that is, the light distribution curve. When the temperature is too high, the blue wavelength will shift and the phosphor wave will become flat and deteriorate, which will lead to a high color temperature and a poor color rendering of LED.
Therefore, due to the high calorific value of LED, its working temperature is high and its performance drops sharply. Only by thoroughly understanding the temperature characteristics of LED, developing the LED chip and LED application products with low thermal resistance can we truly embody the superiority of LED. The structure is a P-N junction of a semiconductor. The experiment points out that when the current flows through the LED element, the temperature of the P-N junction will rise. In strict sense, the temperature of the P-N junction region is defined as the junction temperature of LED. Usually, because the chip of the component has a very small size, we can regard the temperature of the LED chip as junction temperature.