The STTH8R03D is a TURBOSWITCH™ ultrafast rectifier from STMicroelectronics, rated for 300 V reverse voltage and 8 A average forward current in a TO-220AC through-hole package. Its 30 ns reverse recovery time (trr) puts it in the ultrafast class — not just fast-recovery (which the catalog speed category also covers with ≤500 ns), but genuinely fast enough for 100+ kHz hard-switched converters where recovery losses and ringing dominate the efficiency budget. The 1.8 V forward drop at 8 A is the trade-off: you give up a few hundred millivolts compared to a softer-recovery diode to get that 30 ns turn-off. On a PFC boost stage or a secondary-side flyback clamp, that trr figure is what keeps the MOSFET from seeing a current spike on every cycle.
Package and thermal handling — TO-220AC in the real world
The TO-220AC is a two-lead through-hole package with the tab as the anode connection. It bolts to a heatsink with a single screw — common on PFC heatsinks and output rectifier brackets. Without a heatsink, derate aggressively above 100°C case temperature. The lead form is straight for vertical mounting; no right-angle bend option in this variant.