The STTH312B-TR is a 1200 V, 3 A fast recovery diode from STMicroelectronics, housed in a DPAK (TO-252-3) surface-mount package. Its 115 ns reverse recovery time places it in the fast-recovery class, distinct from standard recovery diodes that lack a controlled turn-off. This part is typically specified in power-factor-correction (PFC) boost stages, high-voltage flyback snubbers, and output rectification in switch-mode power supplies where reverse-recovery losses matter at the switching frequency.
115 ns trr — the switching-speed decision
The 115 ns reverse recovery time separates this diode from a standard rectifier. In a continuous-conduction-mode PFC stage, that trr keeps the reverse-recovery charge low enough that the MOSFET or IGBT does not see a current spike at turn-on.
Obsolete — sourcing and replacement planning
If the board can tolerate a package change, the STTH312 family includes other 1200 V, 3 A variants in different packages; confirm the footprint and thermal pad before substituting. No pin-compatible second source is documented in the available records.
DPAK footprint and junction temperature
The DPAK (TO-252-3) package has a tab that carries the cathode current.