At present, the biggest technical problem of LED lighting fixtures is heat dissipation. Poor heat dissipation causes LED driving power and electrolytic capacitors to become the short board for the further development of LED lighting fixtures.
In the luminaire solution using LV LED light source, because the LED light source works at low voltage (VF = 3.2V) and high current (IF = 300 ～ 700mA), the heat is very strong. The space of traditional lamps is small and the area is small. It is difficult for a radiator to dissipate heat quickly. Although a variety of heat dissipation schemes were used, the results were unsatisfactory and became an unsolved problem for LED lighting fixtures. Finding easy-to-use, good thermal conductivity, and low-cost thermal materials is always working.
At present, after the LED light source is powered on, about 30% of the electrical energy is converted into light energy, and the rest is converted into thermal energy. Therefore, it is the key technology for the structural design of LED lamps to export so much heat energy as soon as possible. Heat energy needs to be dissipated through heat conduction, heat convection and heat radiation. Only by expelling the heat as soon as possible can the cavity temperature in the LED luminaire be effectively reduced, the power supply can be protected from working in a persistent high temperature environment, and the LED light source can be prevented from premature aging due to long-term high temperature work.
Heat dissipation of LED lighting fixtures
Because the LED light source itself does not have infrared rays and ultraviolet rays, the LED light source itself does not have a radiation heat dissipation function, and the heat dissipation path of the LED lighting fixture can only derive heat through a heat sink closely combined with the LED lamp bead board. The radiator must have the functions of heat conduction, heat convection and heat radiation.
In addition to any heat sink, it is necessary to quickly transfer heat from the heat source to the surface of the heat sink. The main thing is to radiate the heat into the air by convection and radiation. Heat conduction only solves the heat transfer path, and heat convection is the main function of the heat sink. The heat dissipation performance is mainly determined by the ability of heat dissipation area, shape, and natural convection strength. Heat radiation is only an auxiliary function.
Generally, if the distance from the heat source to the surface of the heat sink is less than 5mm, as long as the thermal conductivity of the material is greater than 5, the heat can be derived, and the remaining heat dissipation must be dominated by thermal convection.
Most LED lighting sources still use low voltage (VF = 3.2V) and high current (IF = 200 ~ 700mA) LED lamp beads. Due to the high heat during work, aluminum alloys with high thermal conductivity must be used. There are usually die-cast aluminum radiators, extruded aluminum radiators, and stamped aluminum radiators. Die-casting aluminum radiator is a technology of pressure-casting parts. Liquid zinc-copper-aluminum alloy is poured into the inlet of the die-casting machine, and then the die-casting machine is used to cast a shape-defined heat sink.
Die-cast aluminum radiator
The production cost is controllable, the heat dissipation wing cannot be made thin, and it is difficult to enlarge the heat dissipation area. The commonly used die casting materials for LED lamp radiators are ADC10 and ADC12.
Extruded aluminum radiator
The liquid aluminum is extruded through a fixed mold, and then the rod is machined to cut into a required shape of the heat sink, and the post-processing cost is relatively high. The heat dissipation wing can be made very thin and the heat dissipation area is maximized. When the heat dissipation wing is in operation, air convection diffuses heat automatically and the heat dissipation effect is better. Common materials are AL6061 and AL6063.
Stamped aluminum radiator
The punching and die stamping and drawing of steel and aluminum alloy plates make it a cup-and-tube radiator. The inner and outer perimeter of the stamped radiator is smooth, and the heat dissipation area is limited due to the lack of wings. Commonly used aluminum alloy materials are 5052, 6061, 6063. The quality of stamping parts is very small and the utilization rate of materials is high, which is a low cost solution.
The heat conduction of aluminum alloy radiator is ideal, which is more suitable for isolated switching constant current power supply. For non-isolated switch constant current power supply, the AC and DC, high voltage and low voltage power supply isolation must be done through the structural design of the luminaire in order to pass CE or UL certification.
Plastic coated aluminum radiator
It is a heat sink with thermally conductive plastic shell and aluminum core. The thermally conductive plastic and aluminum heat sink are formed on the injection molding machine at one time. The aluminum heat sink is used as a buried part and requires machining in advance. The heat of the LED lamp beads is quickly conducted to the thermally conductive plastic through the aluminum heat dissipation core. The thermally conductive plastic uses its multiple wings to form air convection to dissipate heat, and uses its surface to radiate some heat.
Plastic-clad aluminum radiators generally use the original colors of heat-conducting plastics, white and black. Black plastic-plastic aluminum radiators have a better radiation heat dissipation effect. Thermally conductive plastic is a thermoplastic material. The material's fluidity, density, toughness, and strength are easy to injection molding. It has good cold and heat shock cycle resistance characteristics and excellent insulation properties. The thermal conductivity of the thermal plastic is better than that of ordinary metal materials.
The density of heat-conducting plastic is 40% smaller than that of die-cast aluminum and ceramics. The heat sink of the same shape can reduce the weight of plastic-clad aluminum by nearly one-third. Compared with the all-aluminum radiator, the processing cost is lower, the processing cycle is shorter, and the processing temperature is lower; The finished product is not fragile; the customer-supplied injection molding machine can carry out the differentiated design and production of lamps. Plastic-clad aluminum heat sinks have good insulation properties and can easily pass safety regulations.
High thermal conductivity plastic heat sink
Highly thermally conductive plastic heat sinks have recently developed rapidly. Highly thermally conductive plastic heat sinks are all-plastic heat sinks, whose thermal conductivity is several tens of times higher than ordinary plastics, reaching 2-9w / mk, which has excellent heat conduction and heat radiation capabilities. ; New insulation materials that can be applied to a variety of power lamps, can be widely used in various types of LED lamps from 1W to 200W.
High thermal conductivity plastic withstand voltage level up to 6000V AC, suitable for non-isolated switch constant current power supply, HVLED high voltage linear constant current power supply. Make this kind of LED lighting fixture easy to pass the strict safety inspections such as CE, TUV, UL. HVLED uses high voltage (VF = 35-280VDC) and low current (IF = 20-60mA) working state, so the heat of HVLED lamp bead board is reduced. Highly thermally conductive plastic radiators can be used with traditional injection molding and extrusion machines.
One-time molding, high finished product finish. Significantly improve the efficiency of production, flexible design, and give full play to the designer's design concept. The high thermal conductivity plastic radiator is made of PLA (corn starch) polymerization. It is fully degraded, no residue, no chemical pollution, no heavy metal pollution in the production process, no sewage, no exhaust, and meets global environmental protection requirements.
Nano-scale metal ions are densely packed between PLA molecules inside the highly thermally conductive plastic heat sink, which can move quickly at high temperatures and increase heat radiation energy. Its vitality is better than metal heat sink. High thermal conductivity plastic heat sink with high temperature resistance, no cracking or deformation for five hours at 150 ° C. In conjunction with the application of high voltage linear constant current IC driving scheme, no electrolytic capacitors and large volume inductors are needed, which greatly improves the life of the LED lamp. ,low cost. Particularly suitable for the application of fluorescent tubes and high-power industrial and mining lamps.
Highly thermally conductive plastic radiators can be designed with many precise cooling wings. The cooling wings can be made very thin and the heat dissipation area is maximized. When the cooling wings work, air convection diffuses heat automatically and the heat dissipation effect is better. The heat of the LED lamp beads passes through the highly thermally conductive plastic directly to the heat dissipation wing, and the heat is rapidly dissipated through air convection and surface radiation.
High thermal conductivity plastic heat sinks are lighter than aluminum. The density of aluminum is 2700kg / m3, and the density of plastic is 1420kg / m3, which is almost half that of aluminum. Therefore, the weight of a plastic radiator of the same shape is only 1/2 of that of aluminum. Moreover, the processing is simple, and the molding cycle can be shortened by 20-50%, which also reduces the power of cost.