The BSX39 is a silicon planar epitaxial NPN tran-sistor in Jedec TO-18 metal case. It is designed for very fast switching applications up to 500 mA. TO-18 INTERNAL SCHEMATIC DIAGRAM ABSOLUTE MAXIMUM RATINGS Symbol VCBO VCEO VEBO IC Pto t Tstg, Tj Parameter Collector-base Voltage (IE = 0) Collecto.