Single BJT transistor is possible to achieve a high level of efficiency by maintaining the emSingle BJT transistorter base voltage at 5V.A maximum collector current of 100mA volts can be achieved.
BC857BMB,315 Features
the emitter base voltage is kept at 5V
BC857BMB,315 Applications
There are a lot of Nexperia USA Inc. BC857BMB,315 applications of single BJT transistors.