3.3 DC current for Uno and Mega 2560

Forum 2005-2010 (read only) General Uno Punto Zero
5

The dissipation at 150mA assuming it comes after the 5V regulator is 0.15*(5-3.3)=0.255W.
Seeing that the max dissipation at 25C is (125-25)/225[ch8776]0.444W (calculation from datasheet), you can safely pull 150mA.