45 V, 500 mA general-purpose NPN — now obsolete
The Infineon BC817K40WE6327HTSA1 is a general-purpose NPN epitaxial silicon transistor in the SC-70 (SOT-323) surface-mount package. It is rated for a collector-emitter breakdown voltage of 45 V and a continuous collector current of 500 mA, with a power dissipation limit of 250 mW. The DC current gain (hFE) is a minimum of 250 at 100 mA collector current and 1 V Vce, and the transition frequency is 170 MHz. This part is now listed as obsolete by the manufacturer.
What the 45 V breakdown and 500 mA Ic mean for your design
The 45 V Vce breakdown gives comfortable headroom for 24 V and 12 V rails, but the 250 mW power limit in the SC-70 package means the safe operating area is constrained. At 500 mA continuous, Vce(sat) is 700 mV at 50 mA base drive, so the conduction loss in saturation is about 350 mW — above the package's 250 mW rating. For continuous saturation switching, derate the current or pulse the load. The 170 MHz fT is fine for switching up to a few MHz and for audio-frequency amplification.
Infineon has marked the BC817K40WE6327HTSA1 as obsolete. There is no official successor listed in the manufacturer's documentation. For BOM lines that still require this exact order code, the remaining stock in the independent distribution channel is the only option. For new designs or long-term production, a pin-compatible alternative in the BC817 family with the same SC-70 footprint should be qualified.