Hi,

I am using a modified version of the lighting controller circuit at...

Thermal resistance, junction-to-case, R(theta)JC =3D 1.92=B0C/W Thermal resistance, junction-to-ambient, R(theta)JA =3D 62.5=B0C/W Operating and storage junction, temperature range, Tj, Tstg:

-65--150=B0C

With regards to power dissipation, all it says is:

TC =3D 25=B0C =3D> PD =3D 65W derating at 0.52W/=B0C above 25=B0C TA =3D 25=B0C =3D> PD =3D 2.0W derating at 0.016W/=B0C above 25=B0C

Given this, how do I calculate the heatsink I need?

(The maximum current, ideally, is 1.67A, so presumably it's worth working to a maximum of at least 2A, and the maximum voltage across the transistor will be about 16V.)