A voltage generating device includes a mechanically driven generator that is separately excited. An electric starting voltage of the generator is rectified by way of a rectifier. The voltage generating device is closed-loop-controlled by way of a regulating device. A current regulating device has a model of an excitation coil of the generator, and a model value of the electric excitation current of the generator can be ascertained using the model. The current regulating device additionally has a correction element, by way of which the model value of the electric excitation current can be corrected such that the model value of the electric excitation current better matches the actual value of the electric excitation current in a defined manner.