Ok, hot off the development 'floor':
...is the Booster Prototype 2.
This now includes short-circuit protection! The final design will have 2 outputs (for two separate segments of track) at 3Amp each (depending on power supply capabilities.)
There are now 4 status LEDs (Supply Power, Data, Overload, Track Power/Data)
More to come as I finalise the circuit board design.