Hard to tell without the full diagram, but this open collector IC output regulates the opto isolator feedback to maintain equal V+,V-
Vout is ac coupled to a common emitter device with a Shottky diode clamp , so that if there is current spike that exceeds 0.6V/330R it also saturates the collector to turn on the Opto feedback, while the 100K to gnd reduces the turn off time. Since Re is small (47R) and Opto diode pullup is large (1k) it operates as a comparator with high voltage gain for positive spikes only.