Pre-biased NPN in a SOT-23 — what the integrated resistor buys you
The Infineon BCR129E6327 is an NPN pre-biased transistor (BRT) that integrates a 10 kΩ base resistor (R1) in the same SOT-23-3 package. That one resistor eliminates an external passive and a pick-and-place step, shrinking the BOM for simple switching loads up to 100 mA collector current and 50 V collector-emitter breakdown. The 150 MHz transition frequency keeps switching losses low in low-speed relay drivers, LED indicators, and logic-level interface circuits.
At 200 mW maximum power dissipation in the SOT-23 body, the practical continuous collector current sits well below the 100 mA absolute maximum unless you keep VCE low. For a 5 V rail switching a 50 mA load, the VCE(sat) of 300 mV at 500 µA base drive and 10 mA collector current gives a rough dissipation of 15 mW — plenty of margin. Push toward 100 mA at higher VCE, and the junction temperature climbs fast; the 200 mW limit is the hard ceiling for thermal design.