50 ns reverse recovery — the switching-loop enabler
The STTH8R04G is a 400 V, 8 A fast-recovery epitaxial diode from STMicroelectronics, built for hard-switching topologies where recovery charge and reverse recovery time directly impact efficiency and EMI. Its 50 ns trr places it in the ultrafast class, suitable for continuous-conduction-mode (CCM) power-factor-correction boost stages, output rectification in flyback converters, and snubber clamping in motor drives. The 400 V reverse voltage rating gives headroom for universal-input (85–265 VAC) PFC stages, while the 8 A average forward current suits 1–2 kW power supplies when properly heatsinked. The 1.5 V forward drop at 8 A is a typical ultrafast trade-off — lower than a SiC Schottky but higher than a standard recovery diode — so the designer budgets that conduction loss against the switching loss saved by the fast recovery.
175 °C junction — thermal budget for compact PFC
That 175°C ceiling allows the diode to run hotter in a cramped power supply without derating the current — useful when the PFC inductor and bulk cap are sharing the same airflow-starved corner of the chassis. The D2PAK (TO-263AB) surface-mount package with its exposed tab needs a good thermal via stitch to the PCB copper plane; without it, the junction-to-board thermal resistance limits continuous current well below the 8 A rating.
STMicroelectronics lists the STTH8R04G as obsolete. For new designs, a SiC Schottky diode in the same D2PAK footprint (e.g., 650 V / 8 A class) is the common replacement, offering near-zero reverse recovery charge at a higher upfront cost. No last-time-buy window remains; procurement should qualify a substitute or secure inventory for remaining production runs.