Although this short-circuit protection is often sufficient, some applications require a true current limit, such as the implementation in Figure 1′s circuit. A low-value resistor, R1, performs current sensing. The circuit applies the voltage across this resistor, through R2 and R3, to the inputs of the comparator IC2A. R4 and R8 create initial offset voltages to set the current-limit trip point.

Source : http://www.edn.com/archives/1998/052198/11di.htm