What the 27 ns reverse recovery time means for your PFC stage
The STTH50W03CW is a 300 V, 25 A per diode fast-recovery rectifier in a common-cathode TO-247-3 package, built for continuous-conduction-mode PFC and output rectification in high-frequency SMPS. Its 27 ns reverse recovery time (trr) is the key spec that determines switching losses and EMI — a 27 ns trr keeps the recovery snap soft enough that you can run the boost stage at 100 kHz without a snubber on the diode, provided the layout keeps the loop inductance under 20 nH. Each of the two diodes handles 25 A average with a 1.5 V forward drop at that current, so the total package dissipation at full load is roughly 75 W — plan for a heatsink with a thermal resistance below 1.5 °C/W to keep the junction under the 175 °C max.
Package and mounting — TO-247-3 through-hole
The TO-247-3 package is a standard through-hole power package with a large copper tab for heatsink mounting. The common-cathode configuration means the two diode cathodes are tied to the tab, so the tab is at the output voltage — insulate the heatsink or use a thermal pad. The through-hole leads handle the 25 A per diode without issue, but the PCB trace width from the anode pins to the transformer should be at least 5 mm for the return path. The ECOPACK®2 series designation means the part is RoHS-compliant and free of halogens and antimony trioxide, which simplifies compliance for EU and China RoHS.