Overcurrent protection in lab bench power supplies
There are many hobbyist quality schematics out there, so it's harder than one might think to find the schematic for a commercial product. Below is taken from this website. It's a lower end commercial product from an Asian supplier. The overcurrent limit is via the differential comparator IC2D. Very crude current limiting.  



The way it works is pretty straightforward- R3 carries about 20% of the current flowing to the output (R1~R5 are 0.5 ohm resistors), so the voltage across R9+M1+VR1 is proportional to the output current, and that voltage is divided down by R10/R11+VR2 for one side and R24/R25 for the other side. The frequency compensation pin of the LM723 is used for shutdown via D12. 

Offhand, I'm not quite sure what the R23/D9/R23 network achieves. The R22/R23 divider yields nominally a bit under 0.6V unloaded so it would only have an effect if the output voltage was very close to 0V. It might be to prevent a problem with the case of an externally applied voltage to the output that causes it to go negative, which can happen (see D8).