Automotive AEC-Q101 NPN — why the K-40 variant exists
The BC817K-40E6327 is Infineon's AEC-Q101 qualified version of the general-purpose BC817-40 NPN transistor. The 'K' suffix signals the automotive release: this part ships with full PPAP documentation and is traceable to an automotive-grade production line. Rated for 45 V collector-emitter breakdown and 500 mA continuous collector current, it handles relay drivers, solenoid valves, and logic-level interface circuits common in automotive body electronics and engine-management modules. The 170 MHz transition frequency is fast enough for PWM switching up to several hundred kilohertz. Maximum power dissipation is 500 mW, and the junction temperature rating reaches 150 °C — necessary for under-hood ambient conditions where the part may see sustained 85 to 105 °C underhood air.
hFE = 250 minimum at 100 mA — gain margin for saturated switching
The '40' gain bin means DC current gain is guaranteed at a minimum of 250 at 100 mA, 1 V VCE. This is the most important number for the design engineer sizing the base resistor: a 10 mA base drive into a 500 mA load gives a forced beta of 50, well within the saturation rating. At lower collector currents the hFE typically rises, so the same base drive margin holds for lighter loads. The 100 nA maximum collector cutoff current ensures negligible leakage at high temperature, which matters when the transistor drives a load that must stay off during key-off or standby.
Package and footprint: SOT-23-3 (PG-SOT23)
Housed in a standard SOT-23-3 package (Infineon code PG-SOT23), the BC817K-40E6327 is a drop-in footprint match for any BC817-series transistor. The surface-mount package is rated for 500 mW total power — derate for ambient temperature above 25 °C per the thermal resistance curve in the datasheet.
Listed as Active by Infineon.