LED downlight heat dissipation technology explanation

LED downlight heat dissipation technology explanation

With the development of LED downlight lighting products, there are two new technologies: First, in order to increase the luminous flux of a single tube, inject a larger current density, as mentioned below, so that the chip generates more heat and needs to dissipate heat. . Second, the new packaging structure. As the power of the LED light source increases, multiple power LED chip sets are required to be packaged together, such as COB structures, modular lamps, etc., which will generate more heat and require more effective heat dissipation structures and Measures, which puts forward a new topic for heat dissipation, otherwise it will greatly affect the performance and life of LED lamps.

At present, the total heat dissipation efficiency of LED lamps is only 50%, and there is still a lot of electric energy to become heat. Secondly, LED high current density and modular lamps will generate more concentrated waste heat, which requires good heat dissipation.

The main parameters related to heat dissipation are thermal resistance, junction temperature and temperature rise. Thermal resistance refers to the quotient obtained by dividing the difference between the effective temperature of the device and the external specified reference point temperature by the steady-state power dissipation in the device. It is the most important parameter indicating the degree of heat dissipation of the device. At present, the thermal resistance of power LEDs with better heat dissipation is ≤10℃/W, the best thermal resistance reported in China is ≤5℃/W, and the thermal resistance in foreign countries can reach ≤3℃/W. If this level is achieved, the life of the power LED can be guaranteed .

The power of LED lamps, which LEDs need to be considered for heat dissipation, and power LEDs need to dissipate heat. Power LED refers to a light-emitting diode with a working current above 100mA. It is defined by my country's industry standard with reference to the American ASSIST Union. According to the typical forward voltages of the two existing LEDs of 2.1V and 3.3V, that is, the LEDs with input power of 210mw and 330mw or more are power LEDs, and device heat dissipation needs to be considered. Some people may have different opinions, but practice has proved that to improve the reliability (lifetime) of power LEDs, it is necessary to consider the heat dissipation of power LEDs.

There are several different temperature rises for temperature rise, what we are discussing here is: shell-environmental temperature rise. It refers to the difference between the temperature of the LED device shell (the hottest spot that can be measured by the LED lamp) and the temperature of the environment (on the light-emitting plane of the lamp, 0.5 meters away from the lamp). It is a temperature value that can be directly measured, and it can directly reflect the degree of heat dissipation around the LED device. Practice has proven that if the LED case is 60°C when the ambient temperature is 30°C, the temperature rise should be 30°C At this time, the lifetime value of the LED device can be basically ensured. If the temperature rise is too high, the maintenance rate of the LED light source will be greatly reduced.

The junction temperature refers to the temperature of the semiconductor junction of the main heat-generating part in the LED device. It reflects the temperature value that the LED device can withstand under working conditions. To this end, the US SSL plans to establish targets for improving heat resistance. The heat resistance of the chip and phosphor is still very high. At present, the junction temperature of the chip has been reached at 150°C, and the phosphor at 130°C will basically have no effect on the life of the device. It shows that the higher the heat resistance of the chip phosphor, the lower the requirement for heat dissipation.

In order to improve the heat dissipation level, we provide the following suggestions:

1. There are many ways to dissipate heat, such as the use of heat pipes, of course it is good, but the cost factor should be considered, and the cost-effectiveness should be considered in the design.

2. From the perspective of LED chips, new structures and new processes should be adopted to improve the heat resistance of the junction temperature of the LED chips and the heat resistance of other materials, which reduces the requirements for heat dissipation conditions.