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 datasheet describes the heat dissipation structure of the CITIZEN CLLO10 Series LED packages. It explains that the light-emitting diode is mounted directly on a well-conductive aluminum substrate to efficiently transfer heat to an external radiator. The document provides the necessary thermal resistance values and formulas to calculate junction temperature based on input power and ambient conditions.
| Absolute maximum junction temperature | 150°C |
|---|---|
| Heat conductive sheet thickness | 0.12mm |
An external radiator is required because the surface area of the LED package is small and it cannot release much heat into the atmosphere on its own.
The junction temperature (Tj) is calculated using the formula Tj = (Rj-c + Rc-a) * Pd + Ta, where Rc-a is the thermal resistance of the grease and heat sink.