Some basic points of LED optical design (two)

Importance of heat dissipation design

LED itself is a semiconductor device, all semiconductor devices work properly have a certain temperature requirements, including ambient temperature and operating temperature. Generally, the normal working temperature of semiconductor devices is less than 80 degrees, and when the PN junction temperature of LED reaches the temperature of 140 degrees, it will fail. The normal work when its temperature will shine out through a pin or special base, and then through the circuit board or aluminum plate connected to the pin to the surrounding air is emitted out, to ensure the normal operation of LED. In general, a single power is greater than 0.2W, aluminum substrate to do heat dissipation, and then increase the power of aluminum and aluminum radiator. Of course, this is related to the number and density of LED within the entire lamp, too concentrated small power LED also consider the heat dissipation design. It's like every electronic product around you, such as TV sets, monitors, computer hosts, etc.. Heat the incorrect design will directly lead to shorten the life and accelerate the decay speed of LED.

1 now most of the junction temperature limit can be done around 120 degrees, the current Cree should be regarded as high, for the degree of 150.

2 Beads resistance different packaging materials according to the structure, some multi chip tens, single chip is generally a digit, at most ten, of course, which is directly related to the junction temperature is related to the life of LED, an important parameter of the light effect.

3 most of the current LED lamp design life is 20000~50000H, which is determined by a number of factors, such as the life of the first IC to limit the life of the whole lamp.

4 structural layout from the heat is actually the contact thermal resistance and thermal conductivity of the bottleneck, which involves more, not listed. Generally speaking, the structure is one, large area of good contact. PCB is the average distribution of beads as far as possible, avoid heat source concentration.

5 the driving efficiency of course the higher the better, as far as possible on the layout of the principle of maximum heat source is LED lamp. Can be used to glue, etc., to achieve the effect of heat insulation.

Comprehensive consideration: good heat dissipation design temperature rise is best controlled below 35. Junction temperature below 80. Theoretical life of more than 50000.

Current thermal design problems

1 natural heat dissipation by the space is too large (radiation cooling itself is less affected by the size of the space limit).

2 natural heat dissipation area to improve the limited space (convection heat dissipation).

3 are now used to make metal parts radiator, heat conduction in the smaller space is enough. Radiator temperature difference is smaller, less thermal conductivity.

Most of the 4 thermal design focused only on the lamp choice, cooling area, thermal contact resistance, heat radiation. Almost desperate.

5 the current situation, the design of heat dissipation in the lighting system in the design of the heat dissipation, is a practical production and manufacturing, materials accessories, structural modeling and heat dissipation design of a combination of experience.