AEC-Q101 pre-biased NPN in SOT-23 — what it is
The Infineon BCR146 is an automotive-grade NPN pre-biased transistor in a SOT-23-3 package. It integrates two bias resistors — 47 kΩ on the base (R1) and 22 kΩ on the emitter-base (R2) — so you can drop it into a switching circuit without external resistors. Rated for 50 V collector-emitter breakdown and 70 mA continuous collector current, it handles the kind of low-power loads you find in automotive relay pre-drivers, lamp check circuits, and logic-level interfaces. The AEC-Q101 qualification (Series Automotive, AEC-Q101) means it's characterised and tested for the under-hood or cabin environment, not just a commercial-grade part with a sticker.
Built-in resistors — one fewer component per node
The 47 kΩ base resistor and 22 kΩ emitter-base resistor set the transistor's turn-on threshold and speed. For a 5 V logic drive, the base current is roughly (5 V - 0.7 V) / 47 kΩ ≈ 91 µA, which with a minimum DC current gain of 50 at 5 mA collector current gives you plenty of saturation margin. The 22 kΩ resistor across the base-emitter junction speeds turn-off by shunting stored charge — useful in pulsed or PWM applications where you need clean edges. The Vce(sat) of 300 mV at 500 µA base and 10 mA collector is tight enough for low-drop switching.
Sourcing and lifecycle — active, automotive-qualified
It's a current-production part, so there's no last-time-buy pressure. If you're stocking for a long-life automotive program, this is a part you can plan around without worrying about an imminent EOL notice.