Last-time-buy — plan your final order now
Infineon has marked the BC817K40E6359HTMA1 as Last Buy. That means the production window is closing — this is the time to secure lifetime buy quantities or qualify a drop-in replacement before the line goes dark.
Automotive-grade NPN in a SOT-23 footprint
It handles a collector current of 500 mA with a collector-emitter breakdown voltage of 45 V, making it a solid choice for general-purpose switching and driver circuits in engine control units, body electronics, and sensor interfaces where the under-hood temperature range demands a 150°C junction rating. The 170 MHz transition frequency keeps switching edges clean for PWM and low-speed logic-level translation. DC current gain is a minimum of 250 at 100 mA, 1 V — that high gain means you can drive the base with a modest microcontroller GPIO through a single resistor and still saturate the transistor hard.
The 500 mA continuous collector current is the practical ceiling for this device in a SOT-23. The 500 mW power dissipation limit means you need to derate for ambient temperature — at 85°C ambient the available power drops to roughly 60% of the 500 mW maximum. For loads above 300 mA continuous, check the junction temperature against the 150°C rating. Vce(sat) is 700 mV maximum at 50 mA base current and 500 mA collector current. That saturation voltage is typical for a medium-power NPN in this package — budget for the drop when calculating the load voltage in a low-side switch configuration. The 100 nA maximum collector cutoff current is tight enough for most automotive loads; for high-impedance nodes like a wake-up input, that leakage is negligible.