# Calculating required thermal resistance (rsa)

If I have a TO-220, with max power dissipation of 10w and the worst case ambient temp is 50°c, with a $R_{jc}$ of 4°c/w and a max allowed junction temp of 150°c (ignore any thermal resistance between case and heatsink).

Would the heatsink's required thermal resistance $R_{sa}$ be 6°c/w?

• Your calculations are correct, so yes, the maximum required heatsink thermal resistance would be 6ºC/W. – stefandz Sep 5 '15 at 11:59