Automotive-grade NPN transistor for 12 V / 24 V switching
The Infineon BC817K-25WH6327 is an automotive-qualified NPN epitaxial planar transistor in a PG-SOT323-3-1 surface-mount package.
The 45 V Vceo is the maximum voltage the transistor can block between collector and emitter. For a 12 V automotive system, this gives roughly 3× derating against nominal, which is comfortable for suppressing inductive kickback from relays or solenoids without external clamp diodes in many cases. The 500 mA continuous collector current defines the load-driving capacity; at this current the saturation voltage is specified at 700 mV maximum with 50 mA base drive, so base-drive resistor values should be chosen to guarantee at least 50 mA into the base for a 500 mA collector load. The 170 MHz transition frequency is high enough for PWM switching up to several hundred kilohertz, though switching losses will dominate above 100 kHz in a typical gate-drive or DC-DC converter application. The 100 nA maximum collector cutoff current confirms low leakage at high temperature, which matters for circuits that must stay off in standby.