Calculate Junction Temperature

The following is a simple tool to help you evaluate the interplay of the various thermal design parameters that influence junction temperature. In the model, you can enter the thermal resistance values at each step of the path from the array itself to ambient air.

We have laid the model out in two columns. In the left column, you can enter a target junction temperature and calculate the required heat sink capacity. In the right column, you can enter a heat sink capacity and calculate the expected junction temperature.

In both cases, you can change your assumptions about ambient air temperature, type of thermal interface and level of input current. The two-column approach also makes it easy for you to verify maximum junction temperature at the highest expected ambient temperature, while cross-checking what temperatures you can expect on an ongoing basis under normal conditions.

Please feel free to contact us with any questions you might have. We look forward to helping you with your LED thermal management issues.


Rheatsink Tjunction
Forward voltage Vf data input
Current mA data input
Power in We calculated
Power dissipation ratio Pd data input % %
Thermal power Wt calculated
Resistance - LED device Rj-m data input
Resistance - MCPCB Rm-c data input
Resistance - Thermal interface Rc-h data input
Resistance - Heat sink Rh-a calculated input
Junction temperature Tj input calculated
Case temperature Tc calculated
Heat sink temperature Th calculated
Ambient temperature Ta data input