400 V, 1 A fast recovery — what the 30 ns trr buys you
The STTH1R04RL is a 400 V, 1 A fast recovery rectifier from STMicroelectronics in a DO-41 axial package. The 1.5 V forward drop at 1 A is typical for a 400 V fast-recovery part — expect about 1.5 W conduction loss at full rated current, which the DO-41 body can handle with reasonable lead-length derating.
ST lists the STTH1R04RL as obsolete. No last-time-buy window or official successor part number appears on the record. If you have this on a legacy BOM, you are looking at the surplus and broker channel for remaining stock. The DO-41 package and 400 V / 1 A / 30 ns trr parametric set is common enough that several manufacturers offer functionally equivalent fast-recovery diodes — but there is no pin-compatible second source certified by ST. Each replacement needs a board-level qualification, especially for the trr and forward voltage match.
Where you would have used it
This diode was designed for continuous-current mode (CCM) power factor correction boost stages, flyback snubbers, and output rectification in off-line switch-mode power supplies up to about 75 W. The 400 V reverse voltage covers rectified 240 VAC mains with margin. The through-hole DO-41 package is a through-hole legacy form factor — the scorch mark on a dead PSU board often traces to a shorted output rectifier, and this part would have been the original fit.