When the power is dissipated in the semiconductor device, the junction temperature rises.
The temperature rise ΔTj is shown as follows:
ΔTj [deg.C]＝ Rth [deg.C /W] × PLOSS [W]
ΔTj: Junction temperature rise
Rth: Thermal resistance
PLOSS: Power dissipation in the semiconductor device
Junction temperature is shown as follows:
Tj = ΔTj + Ta
Tj: Junction temperature
Ta: Ambient temperature
＊In a bipolar transistor, Tj is used as the symbol of junction temperature.
In a MOSFET, Tch is used as the symbol of channel temperature instead of Tj.
For calculation of junction temperature, please refer to “Thermal Design and Attachment of a Thermal Fin: Power MOSFET Application Notes”