Where does thermal resistance occur?
A1 The thermal resistance (resistance to the conductivity of heat) between the junction and the case is determined by the structure of the device. Therefore, the thermal resistance of this part is treated as a fixed value. The thermal resistance between the case and the ambient air varies greatly according to the mounting conditions. The attachment of a radiator represents the addition of a heat dissipation route from the case surface via the radiator. The concept here is the introduction of thermal resistance via a radiator in parallel with the device’s original thermal resistance between the case and the ambient air. Since the resistance is connected in parallel, it is possible to reduce the thermal resistance between the case and the ambient air by the amount corresponding to the radiator.
