Automotive-grade NPN transistor in SOT-323
The Infineon BC817K40WE6327 is an NPN bipolar junction transistor qualified to AEC-Q101 for automotive applications. It is rated for a collector-emitter breakdown voltage of 45 V and a continuous collector current of 500 mA, with a power dissipation ceiling of 500 mW in the SOT-323 package. The minimum DC current gain (hFE) of 250 at 100 mA collector current and 1 V Vce makes this part suitable for medium-gain driver stages in automotive ECUs, relay drivers, and solenoid actuation circuits where the load current stays under 500 mA. With a transition frequency of 170 MHz, the BC817K40WE6327 can handle switching applications up to several megahertz, though the SOT-323 package limits thermal dissipation in continuous high-current operation.
hFE bin and saturation voltage
The '40' suffix in the order code denotes the hFE bin: a minimum gain of 250 at 100 mA, 1 V. This is the highest gain bin in the BC817 family, useful when base drive is limited or when the design needs to minimize input current from a microcontroller GPIO or sensor output. Maximum Vce saturation is 700 mV at 50 mA base current and 500 mA collector current. In a saturated switch application, the 700 mV drop at full load means the transistor dissipates about 350 mW at 500 mA — close to the package power limit, so derating for ambient temperature is necessary.
Package and thermal considerations
The BC817K40WE6327 is supplied in a PG-SOT323-3-1 package (SC-70 / SOT-323 footprint), a three-lead surface-mount package with a small 2.0 mm × 2.1 mm body. The 500 mW power rating assumes standard FR-4 board copper; for continuous operation near the maximum current, additional copper area on the collector pad or a lower ambient temperature is required. Junction temperature is rated to 150 °C, which allows operation in under-hood automotive environments when the board temperature stays below 125 °C and the power dissipation is derated accordingly.