A pulse-width rectifier for operating an electric machine in motor operating mode or in generator operating mode, includes a terminal for a control device that communicates with the pulse-width rectifier via a data connection. In order to safeguard the supply of energy in the case of a disturbance in the data transmission between the control device and the pulse-width rectifier, the pulse-width rectifier is constructed such that it automatically switches into an emergency generator operating mode in which it produces at its direct-voltage output a prespecified power with which it is possible to maintain at least an emergency operation of electrical consumers.