100 ns trr — fast enough for hard-switching PFC and SMPS
The STTH30R04PI is a 30 A, 400 V fast-recovery epitaxial diode from STMicroelectronics, built with planar technology for low leakage. Its 100 ns reverse recovery time (trr) places it squarely in the class used for continuous-current-mode (CCM) power-factor-correction boost stages and output rectification in 400 V bus converters. The 1.45 V forward drop at 30 A is typical for a 400 V-class fast diode — expect about 43 W conduction loss at full rated current, so the TO-247-like DOP3I package with its insulated tab needs a good heatsink or forced air above 15 A average.
175°C junction — built for the hot end of the board
Rated operating junction temperature from -40°C to 175°C, which is the extended range you see in industrial power supplies, motor drives, and welding inverters — not the 150°C ceiling of commodity fast diodes. That extra 25°C headroom matters when the heatsink is shared with a bridge rectifier or IGBT. Reverse leakage at 400 V is 15 µA at 25°C; it climbs with temperature, but the planar junction keeps it under control well past 125°C.
Obsolete — but the DOP3I footprint still has options
ST lists the STTH30R04PI as Obsolete. No official successor part number appears in the lifecycle record. The DOP3I (also called TO-247AD with insulated tab) is a standard high-power through-hole package, so a parametric replacement from another 30 A, 400 V fast-recovery family with similar trr and the same footprint is the practical path. No last-time-buy window remains; stock is what the surplus channel holds.