Linear regulator heat
A linear regulator does not convert, it burns the difference — so the number that decides whether the part lives is the one nobody prints on it. Twelve volts into 3.3 at half an amp is 4.35 watts in a package the size of a grain of rice.
4.35 W
(12 V − 3.3 V) × 0.5 A = 4.35 W of heat
Package — 62 °C/W. What an AMS1117 arrives in. The figure assumes its tab is soldered to a pour, not to a pad.
In
Out
Efficiency
27%
Junction
295 °C
Headroom
8.70 V
A buck instead
183 mW
4.35 W into the package and 1.65 W into the board — 27% of what you paid for at the wall arrives. At 62 °C/W that is 270 degrees of rise onto a 25 °C bench, so the junction lands near 295 °C against a 125 °C limit. It will not get there: it will fold back, drop out, and read as a board that resets under load. A buck converter would burn 183 mW doing the same job.