Pre-biased NPN — what the integrated resistors save you
The Infineon BCR135E6327HTSA1 is an NPN pre-biased transistor in a SOT-23-3 package. It integrates a 10 kΩ base resistor (R1) and a 47 kΩ base-emitter resistor (R2) on-chip, so you can drive the base directly from a logic output without adding external bias components. Collector current is rated to 100 mA, collector-emitter breakdown to 50 V, and the transition frequency sits at 150 MHz — fast enough for most low-side switching up to a few megahertz.
Maximum power dissipation is 200 mW. In a SOT-23 package on standard FR4, that translates to a thermal resistance around 300–400 °C/W junction-to-ambient. At 100 mA continuous collector current with a 300 mV Vce(sat), the dissipation is 30 mW — well within the budget. But if you run the transistor near its voltage and current limits simultaneously, check the junction temperature. The 200 mW ceiling is the absolute limit; derate for ambient above 25 °C.
The BCR135E6327HTSA1 carries a Last Buy lifecycle status. That means Infineon has announced a final ordering window — once that window closes, the part will no longer be manufactured. If you have an active design using this exact order code, now is the time to secure lifetime buy quantities or qualify a replacement.