20 A fast recovery in a DO-247 — switching loss anchor
The STTH20R04W is a standard fast recovery diode from STMicroelectronics, rated for 20 A average rectified current at 400 V reverse voltage. Its 45 ns reverse recovery time places it in the fast-recovery class, suited for continuous-conduction-mode PFC boost stages, output rectification in medium-frequency SMPS, and freewheeling diodes in motor-drive snubbers where the switching loss budget is dominated by trr.
45 ns trr — snubber and switching loss trade-off
A 45 ns reverse recovery time at 20 A forward current means the diode recovers fast enough to keep turn-off losses manageable in hard-switched topologies up to roughly 100 kHz, depending on the dI/dt and junction temperature. The 1.7 V forward voltage at 20 A sets the conduction loss floor: at full rated current, each device dissipates 34 W in forward conduction alone, so the DO-247 package's junction-to-case thermal impedance becomes the limiting factor for continuous duty.
175°C junction — thermal headroom in tight enclosures
Rated for a maximum junction temperature of 175°C, the STTH20R04W can operate in elevated ambient conditions typical of enclosed power supplies and motor drives. The reverse leakage is specified at 20 µA at 400 V and 25°C, but rises exponentially with temperature — at 125°C junction the leakage can dominate the off-state loss, so the thermal design should budget for the leakage power at the expected hot-spot temperature.
Obsolete — sourcing from surplus and independent channels
STMicroelectronics lists the STTH20R04W as obsolete.