This is simple current limiter. Current limit is easy ajdustable by changing value of 10 ohm resistor and can be calculated with equation current=0.8 (Base-emitter voltage drop)/R(10 ohm resistor) or simply I=0.8/R.
Other resistor (1k in this schematic) is there to limit base current and is calculated by equation R=((source voltage-0.7)*(beta of transistor)/(current limit) or
R=(V-0.8)*B/I.
