Table of Contents
Thermal AnalysisThermal analysis was required since high power LEDs are utilized in the system. Each board contains several 1.4 Watt LEDs, creating a need for heat dissipation. All of the energy consumed (1.4 Watts) is assumed to be dissipated as heat.
Several iterations of finite element analysis were performed, using different parameters and geometries to determine the optimum solution, while also keeping cost of materials and manufacturing low. Natural convection coefficients were determined using theoretical hand calculations, and these boundary conditions were applied to the 3D model. The results are below.
PCB lamination alone, natural convection on both sides
Comparison between mounting the PCB laminations flat against the base plate, or on standoffs
With the standoff configuration, maximum temperature at the base of the LEDs is 369K. With the boards flat mounted that number drops to 351K.
PCB laminations flat against the base plate, with and without neglecting contact resistance
Contact resistance was modeled using a thin solid, with a thermal conductivity that makes it have the same thermal resistance as the contact resistance that would occur between two pieces of aluminum.
This analysis shows that contact resistance is negligible, since the highest thermal resistance is due to convection.
Final design thermal analysis
This analysis shows the results given the 5 board model, contact resistance modeled as thin solids, each LED generating 1.4W, external temperature of 50 degrees C, internal fixture temperature of 60 degrees C, and natural convection on internal and external surfaces. Results show maximum LED surface temperature of 109 degrees C. This is well below the maximum operating temperature of the LEDs of 150 degrees C, even under these worst case conditions.