20 A in a DPAK — what the current rating tells you
The FERD20S100SB-TR is a 100 V, 20 A average rectified FERD diode from STMicroelectronics in a DPAK (TO-252) package. The 20 A rating is the average rectified current at the case temperature — the actual current you can pull continuously depends on the board copper area under the tab and the airflow. At 20 A the forward drop is 780 mV at 10 A, rising with current and temperature, so the conduction loss budget needs a real thermal calculation, not just the headline number.
FERD vs Schottky — the trade-off that matters
A FERD (Field Effect Rectifier Diode) sits between a standard fast-recovery PN diode and a Schottky. It gives a lower forward voltage than a PN diode — 780 mV at 10 A — but with a higher reverse voltage rating than most Schottkys at this current. The reverse leakage is 100 µA at 100 V, which is higher than a PN diode but lower than a Schottky of the same voltage class. If your design runs hot and the reverse voltage spikes above 60 V, the FERD is the better choice over a Schottky; if you need the absolute lowest Vf at low voltage, a Schottky still wins.
175°C junction — where it fits
The maximum junction temperature is 175°C. That puts it in the industrial/power-supply class — rated for the hot side of a PFC stage, a DC-DC converter output, or a motor-drive rectifier bridge where the ambient inside the enclosure hits 85°C or more. The DPAK tab is the thermal path; the datasheet's thermal resistance figures assume a minimum copper pad area on the PCB. If you are laying out a board for this part, budget a 1-inch-square copper pour under the tab with thermal vias to the inner plane.
The DPAK package is a common footprint, so second-sourcing from other manufacturers with a similar 100 V, 20 A rated diode in TO-252 is straightforward if you need a dual-source hedge.