NPN transistor in SOT-23 — 500 mA, 45 V, 170 MHz fT
The Infineon BC 817-25 E6433 is a general-purpose NPN bipolar junction transistor in a SOT-23-3 surface-mount package. The 170 MHz transition frequency keeps switching edges clean for sub-1 MHz PWM and audio-band amplification. The "25" gain group specifies a DC current gain (hFE) of 160 to 400 at 100 mA, 1 V, which gives consistent drive strength across reels. Saturation voltage is 700 mV maximum at 50 mA base current and 500 mA collector current — a reasonable Vce(sat) for a 500 mA device in this footprint. Maximum power dissipation is 330 mW, so derating is needed above 25 °C ambient if the transistor is used in continuous conduction.
Obsolete — plan for a last-time buy or second source
The BC 817-25 E6433 is marked obsolete by Infineon.
Package and temperature — SOT-23, 150 °C junction
The transistor is supplied in a TO-236-3 / SC-59 / SOT-23-3 package, with the Infineon-specific PG-SOT23 designation. It is surface-mount only, solders to a standard SOT-23 land pattern. The junction temperature rating is 150 °C, which covers most industrial and automotive under-hood environments when derated for power dissipation. The 100 nA collector cutoff current (ICBO) at 25 °C is typical for a small-signal NPN; expect it to rise with temperature, but it stays under a microamp for most bias networks.