Fast-recovery diode for PFC and SMPS output stages
The STTH8R04G-TR is a 400 V, 8 A fast-recovery epitaxial diode from STMicroelectronics, built for continuous-current-mode power factor correction (PFC) boost stages and the output rectifier of medium-power switched-mode supplies. The 50 ns reverse recovery time keeps switching losses low at frequencies up to 100 kHz, which is where a standard recovery diode would overheat.
A 50 ns trr at 8 A forward current means the diode clears stored charge quickly when the MOSFET or IGBT turns on, minimising the reverse-recovery current spike that adds to the switch's turn-on loss. In a 100 kHz PFC boost, the difference between a 50 ns and a 200 ns diode can be 5–8 W of saved dissipation in the diode alone. The 1.5 V forward voltage at 8 A is a conduction loss of 12 W at full rated current — the D²Pak tab must be heatsunk to a copper plane or an external heatsink to keep the junction below the 175°C maximum.
The D²Pak (TO-263-3) surface-mount package has a large copper tab that is electrically the cathode. Without that copper area, the 8 A continuous rating derates significantly above 85°C ambient.