A system for protecting against reverse current flow in an output module of an Industrial Process Control System includes a transistor that is driven by a control signal and a current monitor arranged to monitor a current through the transistor. The system includes a processor that is arranged to receive the monitored current and to generate the control signal in dependence upon the monitored current. The processor is configured to turn off the transistor if a reverse current is detected in the transistor. Extension of the system provides a power feed combiner that is protected against reverse current flow.