The STQ2HNK60ZR-AP is an N-channel MOSFET from ST's SuperMESH™ series, rated for 600 V drain-source breakdown and 500 mA continuous drain current in a TO-92-3 through-hole package. The 600 V Vdss is the headline number — it tells you this part is built for off-line auxiliary supplies, bias rails in power-factor-correction stages, or any circuit where the DC bus sits above 300 V and the load stays under half an amp.
Rds(on) and the 3 W thermal ceiling
At 500 mA continuous drain, conduction loss is roughly 1.2 W — well within the 3 W package limit at 25 °C case temperature. But the TO-92-3 has no exposed pad; the junction-to-ambient thermal resistance is high, so any sustained load near the 3 W ceiling requires forced air or a heatsink clip. The 15 nC total gate charge keeps the drive current modest — a 10 V gate signal at 100 kHz draws about 1.5 mA from the driver.