Design Example with TPP7130 in A60 LED bulb heat sink

Transcription

1 Design Example with TPP7130 in A60 LED bulb heat sink Abstract: This article introduces the design example with TPP7130, an insulated thermally conductive plastic with thermal conductivity of 15w/m*K, in A60 LED bulb heat sink. The design is implemented with injection molding, and the result heat sink is tested with 7w, 8w,and 9w LED modules. The temperatures of soldering points of LED components are 63 C, 67 C and 73 C corresponding to 7w, 8w and 9w LED module respectively. Comparison testing are also conducted among different A60 LED bulb with heat sinks of different materials such as aluminia, ceramic etc. 1. High thermally conductive plastics PAKCOOL TPP-7130/TPP-8130 PAKCOOL TPP-8130,TPP-7130 are insulated thermally conductive plastics with highh thermal conductivity(15w/m*k per ASTM E1461),high strength and excellent flexibility (with Nominal Break of 7%), designed for LED lighting market and electronics devices. TPP7130, TPP8130 can meet the requirements of most LED manufactures. TPP7130 is based on PA66. It has been modified with thermal conductivity and flexibility. Besides the LED bulb heat sinks, TPP7130/8130 can be used in plastics cases for power adapter, UPS and other devices that need insulation and heat dissipation. So far most thermally conductive plastics in market are brisk and easy to break when being trimmed after injection molding fabrication, or when applying screws. Chooyu s TPP7130 has been improved to be more flexible. Figure 1 shows the flexibility of TPP7130 with a 3mm thickness sample. The property provides more flexibility for designing and fabrication. Figure 1 2.PAKCOOL TPP-8130 can be used in extrusion processing TPP-8130 is based on PP. The modification type of TPP8130 has been improved with great tensile property, and is the first insulated thermally conductive plastic that can be used for extrusion processing. Used in LED tubes to replace aluminium heat sink, it can be more safe and helpful in heat dissipation.

2 2. TPP7130 in A60 LED bulb heat sink In order to provide reference design for customer in using TPP7130/TPP8130, Chooyu developed a heat sink cup for A60 LED bulb, and assembled with LED boards & LED driver for testing. The result are that the temperatures of soldering poinst of LED components are 63 C, 67 C and 73 C corresponding to 7w, 8w and 9w LED module respectively. Figure TPP7130 PA66 typical properties Typical Properties Color PAKCOOL TPP-7130 Black / White Test Methods Visual Temperature of 0.45MPa 250 C ISO 75:2004 Thermal Conductivity (W/m K) 15 ASTM E1461 Tensile Strength, 1A, 20mm/s (MPa) 20 ISO 527:1993 Tensile Break, 1A, 20mm/s 7% ISO 527:1993 Modulus of Elasticity in Tension, 1A, 20mm/s (MPa) ISO 527:1993 Impact Strength Charpy Notched (kj/m²) 3.5 ISO 179:2000/ 1 e A Impact Strength Charpy Unnotched (kj/m²) 45 ISO 179:2000/ 1 e A Density (g/ cm 3 ) Dielectric Strength (kv/mm) 2.06 ISO ASTM D149 Surface Resistivity (Ω cm) 1x10 14 ASTM D257 Volume Resistivity (Ω cm) 1x10 15 ASTM D257 Flammability (1mm) V0 UL The structure and dimension of the A60 LED bulb heat sink with TPP7130 Because A60 LED bulbs from 7w to 9w are most popular in the market to replace old 100w incandescent lamp, we designed a heat sink with TPP7130 and TPP8130 that can be used in A60

3 LED bulbs. Although TPP7130 has the thermal conductivity of 15W/m*K and high heat radiation capacity, we addd an embedded metal component inside the heat sink to help conduct the heat of LED module to all heat sink so that the heat can be exchanged with circumstance. The embedded metal component is a stretched aluminium barrel with convex-concave to improve the adhesiveness with plastic in injection proceeding, see Figure 3. Figure 3 In LED bulb heat sink, the fins of smooth and straight can absorb the heat emitted from the neighbor fins, which will affect the heat dissipation effects. So we designed the heat sink with fins of slight curly angulations which can lead to spiraling rising air flow to help heat dissipation. In general heat sink design of LED bulbs, the LED driver is installed in a plastic barrel to isolate from the metal heat sink, the plastics barrel are not thermally conductive in most cases. In fact, due to the limited space for LED driver in LED bulbs, the temperatures of some power components can reach up to 90 C, conventional plastic barrel will hold the heat inside, and the temperature of the components will be higher and higher, and that will cause life-time reduction of the LED bulbs. In order to resolve the heat dissipation issue, we use TPP7130 to make the isolated plastic barrels, and the design has been proved successful. We use the glass optical mix mask with the size of 60*54*36, as the light transmittance of glass mixing mask is higher than mixing mask with plastics, even B grade can reach 92% or above. And the heat radiation capacity of glass mixing mask is much higher than that of plastics mixing mask, so that the final bulb can provide better luminous and heat dissipation performance. Figure 4

4 3.3 Special Note when injection processing The injection mold must be pre-heated before injection process. Back pressure of injection machine must be high enough The speed of injection process should be fast so as to reduce the time exposed in high temperature. 3.4 The result heat sink for A Testing Result

5 3.6 Testing comparison among A60 LED bulbs with heat sinks of different material Observations: Under same working condition, the aluminium heat sinks have best heat dissipation performance. The heat dissipation performance of heat sink of TPP7130/8130 embedded with metal component has achieved or even better than the performance of same size heat sink with 96 ceramic. Despite the fact that the thermal conductivity of 96% ceramicc is 24.7W/m*K, and the thermal conductivity of TPP7130/TPP8130 is only 15W/m*K, and when embedded with metal component, TPP7130 heat sink excels the test. The heat dissipation effect when using LED chips of 0.5W/pcs or 0.3W/pcs is much better than when using high power LEDs. 4.Conclusion Thermally conductive plastics can be used in LED bulbs with power range up to 10w. Although the heat dissipation performance of thermally conductive plastics is not as good as aluminium heat sink, it can help customers in CE certification with its insulation features. And it is more suitable for mass production by using injection processing.