55 V, 3.7 A N-channel in a SOT-223 — what this part is for
The IRFL4105TRPBF is an N-channel enhancement-mode MOSFET from the HEXFET series, rated for 55 V drain-to-source and 3.7 A continuous drain current at 25°C. It comes in a surface-mount SOT-223 package (TO-261-4), which keeps the board footprint small for low-to-moderate power switching. The 45 mOhm maximum on-resistance at 10 V gate drive is the headline number for conduction loss — at 3.7 A that's about half a watt of dissipation, within the 1 W package limit. Typical applications include load switches, DC-DC converter input stages, and low-side switching in industrial control boards where board space is tight and the rail stays under 55 V.
Package and mounting
The 45 mOhm Rds(on) is specified at 10 V gate drive and 3.7 A drain current. That's the standard 10 V drive level for logic-level gate thresholds — the part's Vgs(th) max is 4 V at 250 µA, so 10 V gives you a solid overdrive. The 35 nC gate charge at 10 V is moderate; a typical gate driver with 1 A peak output can switch it in a few hundred nanoseconds. Input capacitance is 660 pF at 25 V Vds, which is low enough that a microcontroller GPIO through a series resistor can drive it for low-frequency switching, though a dedicated driver cleans up the edges for higher-frequency PWM.
Temperature range and environment
Junction temperature range is -55°C to 150°C, covering industrial and some automotive under-hood environments. The 1 W power dissipation at 25°C ambient is the package limit in free air; derating is needed above that. In a forced-air or heatsinked layout, the SOT-223 can handle more, but the 1 W number is the conservative design-in figure. ROHS3 compliant, no lead or restricted substances.
Active lifecycle — no LTB concern
The IRFL4105TRPBF is listed as Active in production. No last-time-buy or end-of-life notices are in the record. The part is ROHS3 compliant. For BOM planning, this means no near-term obsolescence risk — it's a standard catalog MOSFET that's been in the channel for years and should remain available through normal distribution.