Analysis of LED passive cooling scheme

Introduction: LED passive heat is mainly suitable for medium and small power LED to heat. Since no additional power consumption is required, the overall efficiency of the application is not affected.

Natural cooling

The principle of natural heat dissipation is to add heat sink on the outer side of the substrate, and heat the chip to heat the heat through the heat conduction.

Basic formula of heat conduction:

In the formula, Q is the heat, heat is heat conduction; K heat conduction coefficient of the material, the heat conduction coefficient is high, the value of specific heat is low; A is the heat transfer area (or contact area of two objects); T is the temperature difference across the delta L at both ends; the distance. Therefore, it can be found from the formula that the size of the heat transfer is proportional to the heat transfer coefficient, heat transfer area, the temperature difference between the two ends, and the distance is inversely proportional to the distance. That is to say, the material of the radiator should have a high thermal conductivity, and its temperature rise is low, the specific heat is large, generally with high thermal conductivity and heat capacity of large materials (copper, aluminum) made (see Table 1).

The basic formula of thermal convection:

In the formula, Q is the heat, that is, the heat carried away by the thermal convection; H is the numerical value of the thermal convection; A is the effective contact area of the thermal convection; the T is the temperature difference between the solid surface and the region fluid. Therefore, the heat transfer is proportional to the heat convection coefficient, the effective contact area and the temperature difference. In order to increase the heat dissipation effect, namely, increasing the contact area between the surface and air, the outer surface of the radiator can be made into a fin shape. Fin shape also has a variety of quantity, and the fin position, size, inclination angle and thickness etc. need to be carefully studied, in addition to common and straight, wavy, spiral, cylindrical and conical, this is not the only one. The purpose is to facilitate the air convection and rainfall, to obtain the best cooling effect. In the use of materials, thermal conductivity of copper is much faster than aluminum, copper aluminum heat but no fast, thus forming a copper aluminum composite radiator - model combining the advantages of the copper aluminum, copper can quickly put the high calorie LED chip to aluminum, the aluminum fin a large area of the heat dispersed, so as to achieve better cooling effect.