500 V, 8 A N-channel — the TO-220 workhorse for offline power stages
The IRF840APBF is a Vishay N-channel power MOSFET in a TO-220AB through-hole package, rated for 500 V drain-source breakdown and 8 A continuous drain current at 25°C case temperature. It targets high-voltage switching applications such as flyback converters, offline AC-DC power supplies, and motor drive circuits where the 500 V blocking voltage provides margin for rectified 240 VAC rails. With a maximum on-resistance of 850 mOhm at 4.8 A and 10 V gate drive, conduction losses stay manageable for loads up to a few amps. The 38 nC total gate charge keeps the gate-drive power low at moderate switching frequencies — a practical fit for 50–100 kHz hard-switched topologies.
Gate drive and switching — what the numbers mean at the bench
The 10 V gate drive voltage is specified for both the maximum and minimum Rds(on) — this part expects a full 10 V gate signal to achieve the rated on-resistance. The gate threshold is 4 V maximum at 250 µA drain current, so a 5 V logic-level gate drive will not fully enhance the channel; plan for a dedicated gate driver or a bootstrap supply above 10 V. Input capacitance is 1018 pF typical at 25 V drain-source — a moderate figure that does not require a heroic gate-driver for switching frequencies under 100 kHz. The 38 nC gate charge translates to roughly 3.8 mA average gate-drive current at 100 kHz, well within the capability of a standard MOSFET driver like the TC4427.
Thermal handling and package rework
Maximum power dissipation is 125 W at the case, but the real thermal limit depends on the heatsink. The TO-220AB package has a metal tab that must be electrically isolated or connected to the drain node — the tab is the drain. For rework, the through-hole leads are easy to desolder with a solder sucker or wick; the tab can be soldered to a PCB pad or bolted to a heatsink with a TO-220 mounting kit.