An exemplary power supply system for a direct-current drive includes a power converter for at least one direction-dependent two-quadrant operating mode, at least one associated pulse-based actuation device, an input-side connection and an output-side connection for the power converter, and at least one mechanical interruption device for the input-side connection and/or the output-side connection. The power supply system is provided to continually provide values of a current flowing on the output-side during operation by receiving an STO (safe torque off) signal, immediate changeover of the power converter operating mode into the inverter limitation if an STO signal is received, interrupting a feed of actuation power through the actuation device into the power converter, and supplying an interruption signal to the at least one mechanical interruption device once a second subsequent time interval has elapsed and the current flowing on the output side has not decayed below a safety-critical limit value.