The STTH8S12D is a 1200 V, 8 A fast-recovery epitaxial diode from STMicroelectronics in a TO-220AC package. Its headline rating is the 45 ns reverse recovery time (trr), which places it in the ultrafast class despite the standard 'Fast Recovery' category label. That trr is measured at the 8 A forward current and 1200 V blocking voltage — the same conditions you see in a power-factor-correction boost stage or a 3-phase inverter freewheel leg. The 2.7 V forward drop at 8 A is a tradeoff: you trade a higher Vf for the fast turn-off that cuts switching losses in hard-switched topologies.
1200 V blocking and 175°C junction — fit for industrial and traction auxiliaries
With a 1200 V DC reverse voltage rating and a 175°C maximum junction temperature, this diode is sized for the high-voltage rails found in industrial motor drives, solar inverters, and auxiliary supplies in railway or EV traction systems. The 5 µA leakage at 1200 V is a room-temperature typical; expect it to rise with junction temperature, but the 175°C Tj headroom gives you margin when derating for a 105°C ambient inside a sealed enclosure.
STMicroelectronics lists the STTH8S12D as an active product. That means no last-time-buy window to track, no risk of a sudden EOL notice during a production run. For a procurement desk qualifying this into a power-stage BOM, the active status removes the single-source lifecycle risk that haunts older fast-recovery diodes.