The light-emitting diode of an LED package radiates light and heat according to the input power. However, the surface area of an LED package is quite small,and the package itself is expected to release little heat into the atmosphere.An external radiator such as a heat sink is thus required.The heat dissipation structure up to the connection portion of the external radiator uses mainly heat conduction.
This document describes the detailed heat dissipation structure of the CITIZEN CLLO30 series LED packages. It explains how the package minimizes thermal resistance between the junction and the case to efficiently conduct heat to an external radiator.
The text provides formulas for calculating junction temperature based on input power, ambient temperature, and thermal resistances. It includes charts correlating ambient temperature with allowable external thermal resistance for various models (CLLO30-1205A1 through CLLO30-1212A1) and presents simulation results regarding heat sink surface area and input power.
| Absolute maximum junction temperature | 150°C |
|---|---|
| Thermal resistance Rj-c (CLLO30-1205A1) | 1.7 °C/W |
| Thermal resistance Rj-c (CLLO30-1206A1) | 1.5 °C/W |
| Thermal resistance Rj-c (CLLO30-1208A1) | 1.2 °C/W |
| Thermal resistance Rj-c (CLLO30-1212A1) | 0.8 °C/W |
The junction temperature Tj can be calculated using the formula: Tj = Rj-c * Pd + Te.
As ambient temperature and driving current increase, the allowable thermal resistance outside the package must decrease to prevent overheating.