Switching power between two 7-segment displays using NPN transistors
You could use an emitter follower and drive it from a 5V input. It will drop one Vbe drop, about 0.7V, so the power dissipation at 150mA would be about 100mW, which should be okay for most transistors over a reasonable temperature range. Use a pull-up resistor on the base if you don't have something like an HCMOS driver. 







simulate this circuit &ndash; Schematic created using CircuitLab

The 100R base resistor is sort-of optional, but in some cases the emitter follower can oscillate at VHF frequencies if you give a really stiff base voltage, and the resistor will prevent that.