30 ns reverse recovery — what it buys you
The STTH4R02RL is a 200 V, 4 A fast-recovery rectifier from STMicroelectronics built on standard planar technology. The 1.25 V forward drop at 12 A is a pulsed rating — the continuous 4 A average is the number to size the heatsink against.
ST lists the STTH4R02RL as obsolete.
Package and thermal fit
The DO-201AB axial-lead package (also known as DO-32) is a through-hole form factor that clips into a heatsink or solders into a board with lead bending. Junction temperature is rated to 175 °C max, which gives headroom in high-ambient environments like enclosed power supplies or motor-drive cabinets — but the 4 A continuous rating needs derating above 100 °C case temperature, typical for this package class.