An electrostatographic printing apparatus comprises a charge receptor, and a transfer station for transferring a toner image from the charge receptor to a sheet by providing an electric field of predetermined magnitude at a transfer zone. The transfer station includes a rotatable transfer member, with a cleaning corotron associated therewith. A control system for maintaining a constant current at the transfer zone takes into account a current supplied by the cleaning corotron. The control system can also take into account current leakages associated with the transfer member.