The Infineon BC 817-40 B5003 is an NPN bipolar junction transistor in a standard SOT-23 surface-mount package. It is designed for general-purpose switching and amplification in low-power circuits, with a collector-emitter breakdown voltage of 45 V and a continuous collector current rating of 500 mA. The 170 MHz transition frequency suits it for driver stages and signal conditioning up to the low-MHz range.
The 45 V Vce breakdown gives enough headroom for 12 V and 24 V rails, but it is not a 60 V or 80 V part — do not use it where transients can exceed that ceiling. The 500 mA Ic rating covers moderate loads like relay coils, LED strings, and small solenoids, but it is not a power transistor; the 330 mW dissipation limit means derating is required above 25 °C ambient. The 170 MHz fT is adequate for switching regulators in the 100–500 kHz range and for audio preamp stages, but not for RF power applications.
Lifecycle status — obsolete, no official successor
The BC 817-40 B5003 is marked obsolete by the manufacturer. For new designs, consider a current-production NPN transistor in SOT-23 with similar ratings, such as the BC 817-25 or BC 817-16 variants (different hFE binning) or the BC 847 series, but verify pin compatibility and hFE range for your circuit.
Package and mounting — SOT-23 footprint
The BC 817-40 B5003 is supplied in a TO-236-3 / SC-59 / SOT-23-3 package, with the Infineon code PG-SOT23. It is a surface-mount device with three leads. The small footprint is standard for low-power discrete transistors and is compatible with most pick-and-place and reflow processes.