The 500 V Vdss sets the absolute maximum drain-source voltage the device can block in the off state. For a universal-input flyback (85–265 VAC), the reflected voltage plus leakage spike typically reaches 450–500 V, so this part sits right at the margin — a 600 V rated device would give more headroom, but the STD3NK50ZT4 works if the snubber is well-tuned and the leakage inductance is controlled. The 2.3 A continuous current at 25°C case derates to about 1.5 A at 100°C case temperature (using the 45 W maximum power dissipation and the junction-to-case thermal resistance from the datasheet), so the load current in the application must stay below that derated value to keep the junction under 150°C.
Package and mounting — DPAK (TO-252-3)
The STD3NK50ZT4 comes in the DPAK (TO-252-3) surface-mount package with two leads and a tab that forms the drain connection.
The device is RoHS compliant per the standard ST EU declaration, and the base product number STD3NK50 covers the DPAK variant in the SuperMESH™ family.