400 V, 3 A — the application envelope
The GBU4G-E3/45: Rated for 400 V peak reverse voltage and 3 A average rectified output current, this part handles low-power AC-to-DC conversion in off-line supplies up to roughly 100 W (derated for ambient and heatsinking). The 1 V forward drop at 4 A (specified at a higher test current than the average rating) gives a conduction loss of about 3 W at full load — the GBU package's copper lead frame and through-hole mounting dissipate that into the board or a clip-on heatsink. Reverse leakage is 5 µA at the 400 V blocking voltage — negligible for most designs, but worth noting if the application runs at elevated junction temperature where leakage doubles per 10°C rise.
Through-hole GBU — board integration
The 4-SIP GBU package (4-pin single in-line, 20.0 mm body length typical) mounts through-hole with a standard 5.08 mm pitch between the AC input and DC output pins. The tube packaging is the factory shipping format — 20 pieces per tube for the GBU4G-/45 variant. No reel or tape-and-reel option is listed; for automated assembly, the tube feed requires a tube handler or manual loading.