Calculate max. power dissipation and with and without heatsink.

$\theta_jc$ = 1.75° c/w , $\theta_cs$ = 1° c/w , $\theta_ca$ = 50° c/w

$\theta_sa$ = 5° c/w , $t_jmax$ = 150°c and $t_amb$ = 30°

When no heat sink is used, the max device power dissipation is found as,

P D max = $\frac{T_JMAX = T_AMB}{\theta dev – Case + \theta Case – amb}$

= $\frac{150 – 30}{1.75 + 50}$ = 2.32 w

When a heat sink is used, the max device power dissipation is found as,

P DMAX = $\frac{T JMAX – T AMB}{\theta dev-Case + \theta Case-Sink + \theta Sink-amb}$

= $\frac{150 – 30}{1.75 + 1 + 5}$ = 15.5 w