The STTH3L06RL is a 600 V, 3 A fast-recovery epitaxial diode from STMicroelectronics, housed in a DO-201AD axial-lead package. Its 85 ns reverse recovery time (trr) qualifies it for switching power supplies, power factor correction (PFC) boost stages, and flyback output rectification where the diode must turn off cleanly to keep switching losses and EMI under control.
The 85 ns reverse recovery time is the headline spec for this class of diode. In a hard-switched PFC or flyback converter, trr determines the reverse-recovery charge that the MOSFET must absorb at turn-on. A faster trr reduces the current spike and the associated switching loss. At 85 ns this diode is a standard-speed fast recovery part — adequate for line-frequency PFC (50–60 kHz switching) and moderate-speed flybacks, but not intended for multi-hundred-kHz resonant or LLC converters where sub-30 ns parts are typical.
Voltage and current — sizing the BOM slot
Rated 600 V reverse and 3 A average forward current (Io), this diode fits the boost rectifier in a 300 W-class PFC stage or the output rectifier in a 150 W flyback. The forward voltage drop is 1.3 V at 3 A — moderate for a 600 V part, so the thermal design should budget about 3.9 W conduction loss at full load. The DO-201AD axial body is through-hole, which simplifies heatsinking with a clip-on or board-mount heat spreader.
Obsolete — the sourcing reality
STMicroelectronics lists the STTH3L06RL as obsolete. For a BOM that already specifies this diode, the procurement path is the independent distribution channel — surplus and new-old-stock lots. If the design is still in development, a cross-reference to an active 600 V, 3 A fast recovery diode in DO-201AD should be evaluated to avoid a future last-time-buy scramble.