What the 95 ns reverse recovery time buys you
The STTH512FP is a 1200 V, 5 A fast-recovery diode from STMicroelectronics, built for the high-voltage side of power supplies, PFC stages, and motor-drive snubbers. Its 95 ns reverse recovery time puts it in the class that can handle hard-switching transitions without cooking the junction — a standard recovery part would still be conducting during the voltage rise, burning extra watts and ringing the node. At 5 A average rectified and a forward drop of 2.2 V at that current, the conduction loss is predictable; the fast recovery keeps the switching loss from dominating the thermal budget.
1200 V blocking — derating headroom for 400 V rails
The 1200 V DC reverse rating covers the usual 400 VDC bus plus a healthy safety margin for transients and ring-back. In a PFC boost stage running a 400 V output, the diode sees peak reverse stress near the bus voltage plus the switching overshoot — 1200 V buys the design margin to skip an extra snubber in many cases. The junction temperature max of 175 °C is standard for fast-recovery silicon; keep the heatsink sized so the junction stays below 150 °C in steady state to preserve the 95 ns recovery speed.
Package and mounting — isolated tab matters
The TO-220-2 Full Pack with isolated tab means the metal back is electrically isolated from the cathode — no insulating pad or washer needed between the diode and the heatsink. That simplifies assembly and improves thermal transfer in a crowded PFC or inverter stage. The supplier device package is TO-220FPAC; it is a through-hole mount, so expect to hand-place or wave-solder it. The isolated tab also cuts the risk of a heatsink-to-ground short if the diode fails short-circuit.
Active production — no end-of-life scramble
The base product number is STTH512, and the FP suffix identifies the full-pack isolated-tab variant — make sure your BOM calls out the FP suffix if you need the isolated tab, because the non-isolated TO-220 version (STTH512) has a different thermal mounting requirement.