800 V, 2 A, 75 ns — PFC boost rectifier fit
The STTH208U: The 75 ns reverse recovery time (trr) places it in the fast-recovery class — fast enough for continuous-conduction-mode PFC boost stages in offline power supplies up to about 100 kHz, where the recovery charge does not dominate the switching loss. The 800 V Vrrm gives 2× derating margin over a 380 VDC PFC bus, covering universal-input (85–265 VAC) designs without an additional series diode.
Forward drop and thermal budget at 2 A
Forward voltage is 1.65 V maximum at 2 A, producing 3.3 W conduction loss at full rated current. The SMB package junction-to-ambient thermal resistance is typically 75–90 °C/W on a standard FR-4 pad — at 3.3 W the junction rises 250–300 °C above ambient, which exceeds the 175 °C Tj max unless the board provides a larger copper heatsink area or forced airflow. In practice the part is derated to about 1 A continuous in still air at 85 °C ambient. The 175 °C maximum junction temperature is a die-level limit; the solder joint reliability at sustained operation above 150 °C is the board-level constraint. For high-temperature environments (engine bay, industrial oven controls), the derating curve in the ST datasheet should be consulted for the actual allowable current at the target ambient.
Package and board integration
Supplied in DO-214AA SMB, a standard surface-mount package with a 0.208-inch body width. The cathode is marked by a band on the body; polarity is not indicated on the reel label. The SMB footprint is shared across many ST fast-recovery diodes in the STTH family — the STTH208U is the 800 V, 2 A variant. The pad layout follows the standard JEDEC SMB land pattern; no special thermal vias are required for currents below 1 A continuous.
The base product number is STTH208; the 'U' suffix indicates the SMB package variant.