1200 V / 5 A fast recovery diode — the snubber and PFC choice
The STTH512B is a 1200 V, 5 A fast recovery rectifier from STMicroelectronics in a DPAK (TO-252-3) surface-mount package. Its 95 ns reverse recovery time (trr) makes it suitable for continuous-conduction-mode PFC boost stages, flyback snubbers, and output rectification in 1–2 kW switch-mode power supplies where reverse-recovery losses dominate the switching loss budget. Reverse leakage is 5 µA at 1200 V, a low figure that helps standby efficiency in off-line supplies.
STMicroelectronics lists the STTH512B as obsolete. For new designs, a same-function 1200 V, 5 A fast recovery diode in DPAK from ST's current portfolio (e.g., the STTH5L12 series) or from competitors (Vishay, ON Semiconductor) should be evaluated.
A 95 ns trr at 5 A forward current and 1200 V blocking means the diode recovers quickly enough for switching frequencies up to about 100 kHz in hard-switched topologies before reverse-recovery losses become the dominant loss mechanism. In a 100 kHz PFC boost, the recovery charge (Qrr) will be roughly 0.5 µC, which the MOSFET must absorb each cycle — a figure that keeps the switching node ringing within acceptable bounds with a properly damped snubber.