The STTH1R04QRL is a 400 V, 1 A fast-recovery rectifier from STMicroelectronics, built for the high-frequency side of offline power supplies. The 1.5 V forward drop at 1 A is typical for a 400 V-class fast diode — the trade-off for the speed is a slightly higher Vf than a standard recovery part, but the recovery charge saved at 50–100 kHz more than compensates in efficiency.
175°C junction — thermal headroom for dense layouts
Rated for a maximum junction temperature of 175°C, the STTH1R04QRL gives thermal margin in designs where the diode shares a cramped heatsink or sits near a hot MOSFET. The 5 µA reverse leakage at 400 V is specified at 25°C; expect that to multiply with temperature, so the leakage power contribution should be checked against the thermal model at the full 175°C limit. The DO-15 axial package is a through-hole format that suits point-to-point wiring on heatsink tabs or terminal blocks in industrial power modules.
STMicroelectronics lists the STTH1R04QRL as Active. The base product number STTH1 covers a family of 1 A fast-recovery diodes with voltage options from 200 V to 600 V; the R04 suffix in this variant specifies the 400 V rating.