What this PNP transistor is and when you pick it
The Infineon BC 807-40 E6433 is a PNP general-purpose switching transistor in a SOT-23 surface-mount package. It is the high-gain variant (hFE grade 40) of the BC 807 family, with a minimum DC current gain of 250 at 100 mA collector current and 1 V VCE. The 45 V collector-emitter breakdown and 500 mA continuous collector rating place it in the medium-power small-signal class — suitable for driving relays, small solenoids, LED arrays, and as a high-side load switch where a PNP pull-up is needed. The 200 MHz transition frequency keeps switching losses low in sub-MHz PWM applications like fan control or dimming.
The 500 mA collector current — what it can and cannot drive
The 500 mA continuous collector current is the absolute limit, not a recommended operating point for sustained use. For a 24 V relay coil drawing 200 mA, this transistor has comfortable margin. For a 500 mA solenoid, you are at the ceiling — derate for ambient temperature and consider a TO-252 or larger device. The 330 mW power dissipation in the SOT-23 package is the real constraint: at 500 mA and 0.7 V VCE(sat), you are already at 350 mW, exceeding the package rating. Practical continuous current is lower, around 300 mA, before the junction temperature climbs above 150°C.
Gain of 250 — why this matters for logic-level drive
The minimum hFE of 250 at 100 mA means a base current of only 400 µA is needed to saturate the transistor at that collector current. A 3.3 V GPIO through a 6.8 kΩ series resistor delivers that easily. This is the advantage of the -40 gain grade over the -16 or -25 variants — you can drive heavier loads directly from a microcontroller pin without a pre-driver transistor. The VCE(sat) of 700 mV at 50 mA base, 500 mA collector is typical for a saturated PNP in this class.
SOT-23 footprint and second-source reality
The SOT-23 (TO-236-3 / SC-59) footprint is ubiquitous. The Infineon PG-SOT23 variant is pin-compatible with the industry-standard BC807-40 from Nexperia, ON Semiconductor, and Diodes Inc. If you are replacing a BC807-40 from another manufacturer, the mechanical fit is identical — same 1.9 mm pitch, same 2.9 x 1.3 mm body. The electrical specs are interchangeable across suppliers for the -40 gain grade.
Infineon lists the BC 807-40 E6433 as obsolete. For a production BOM, you need a replacement or a surplus-channel source. For existing designs, the surplus market carries inventory, but expect pricing above the original factory level and no guaranteed long-term availability.