In prior calculations, the maximum impedance allowed between the junction and ambient air was 27°C/W. Subtracting the impedance of the junction-to-case (0.5°C/W) and the impedance of the case-to-sink (0.45°C/W), the maximum allowance left over for the heat sink is 26.05°C/W (calculated as 27°C/W minus 0.5°C/W minus 0.45°C/W). The thermal impedance of 19.1°C/W for this heat sink under the assumed conditions is well below the previously-calculated allowance of 26.05°C/W. This translates to a cooler silicon junction temperature inside the TO-220 package and more thermal margin in the design. The maximum temperature of the junction can be estimated by adding up all of the thermal impedances, multiplying them by the number of Watts dissipated in the junction, and adding the result to the maximum ambient temperature. The result in this example is an estimated junction temperature of 105.7°C with a heat sink. This shows the dramatic impact a heat sink can have on an application when compared to the 222°C junction temperature calculated earlier without a heat sink.