650 V N-channel MOSFET for offline SMPS primary side
The STF12N65M5 is a 650 V N-channel power MOSFET from STMicroelectronics' MDmesh™ V series, packaged in a TO-220-5 Full Pack (TO-220FP) with isolated mounting tab. The 650 V drain-source voltage rating suits it for the primary side of single-switch flyback, PFC boost, and half-bridge LLC converters operating from universal AC input (85–265 VAC) with adequate derating headroom for line transients.
On-resistance and gate charge — switching loss trade-off
The low gate charge reduces drive current requirements at high frequency — a 22 nC gate charged at 100 kHz draws roughly 2.2 mA average from the gate driver, keeping the bootstrap capacitor voltage stable.
Thermal limits and package reality
Maximum power dissipation is 25 W at case temperature, limited by the TO-220FP's insulated tab. The junction temperature rating of 150 °C means the design must keep the junction below that under worst-case load and ambient — the 25 W ceiling translates to a junction-to-case thermal resistance of about 5 °C/W, typical for a full-pack TO-220. The through-hole TO-220FP package (TO-220-5 Full Pack) provides a fully isolated backside tab — no insulating washer needed, which simplifies assembly and improves thermal coupling to a heatsink. The 5-lead variant includes a dedicated sense pin (if present) or Kelvin source connection for accurate gate-drive return.
ROHS3 compliant per, with no exemptions that would complicate EU or RoHS-restricted markets. No stock-holding claim; the part is procured per BOM quantity.