The Infineon BCR 503 B6327 is an NPN pre-biased transistor in a SOT-23-3 package. It integrates two 2.2 kOhm resistors — one in series with the base, one between base and emitter — which eliminates the need for external bias components in low-side switching and driver applications. The transistor is rated for a 500 mA collector current and a 50 V collector-emitter breakdown voltage, with a transition frequency of 100 MHz. Typical uses include relay and solenoid drivers, LED switching, and logic-level interface circuits where board space is tight.
Package and mounting
Both R1 (base resistor) and R2 (base-emitter resistor) are 2.2 kOhms. This ratio sets the transistor's turn-on threshold: with a 5 V logic drive, the base current is roughly (5 V - 0.7 V) / 2.2 kOhm ≈ 2 mA, which is enough to saturate the transistor at collector currents up to about 50 mA. The DC current gain minimum is 40 at 50 mA collector current and 5 V Vce, so the integrated resistors are sized for typical digital I/O drive levels. The 100 nA maximum collector cutoff current means the transistor stays firmly off when the base is pulled low.