45 V, 20 A FERD — where the 550 mV Vf matters
The STMicroelectronics FERD2045SB-TR is a 45 V, 20 A Field Effect Rectifier Diode in a DPAK (TO-252-3) surface-mount package. Its 550 mV maximum forward voltage at 20 A sets the conduction loss floor for low-voltage, high-current secondary-side rectification — think 12 V to 24 V output rails in AC-DC converters, OR-ing diodes in redundant supplies, and reverse-polarity protection where every millivolt of drop eats into the output headroom.
FERD vs Schottky — the leakage trade-off
A conventional Schottky at 45 V and 20 A would typically show higher reverse leakage at elevated junction temperatures. The FERD (Field Effect Rectifier Diode) structure trades a slightly higher Vf for significantly lower leakage at 150°C — the 600 µA at 45 V reverse is about an order of magnitude lower than a comparable Schottky at the same temperature. That matters when the diode sits in a thermally constrained enclosure or shares a heatsink with other hot devices.
The ECOPACK®2 series designation confirms RoHS compliance and a halogen-free mould compound.
Package and thermal — DPAK footprint realities
The DPAK (TO-252-3) has an exposed copper tab on the bottom — the tab is the cathode. The datasheet's thermal resistance junction-to-ambient assumes a minimum copper pad area on the PCB; a 1-inch-square pad on a 2-oz copper board drops RthJA by roughly 40% compared to a minimal footprint. Without that, the junction will exceed 150°C at full load.