30 ns recovery — the switching loss number
The STTH806DTI is an STMicroelectronics ultrafast recovery diode rated 600 V reverse and 8 A average rectified current. Its 30 ns reverse recovery time places it in the fast-switching class needed for PFC boost stages, SMPS output rectification, and flyback snubbers where stored charge in the junction directly eats into efficiency.
Forward drop and thermal budget
Maximum forward voltage is 3.6 V at 8 A — a deliberate trade-off that keeps the die small and the recovery fast. At full rated current the conduction loss is about 29 W peak, which the TO-220AC insulated package must sink through the tab. Junction temperature is rated to 175 °C max, so the heatsink needs to hold the case temperature below about 150 °C at full load to stay inside the SOA.