The present invention relates to X-ray generating technology in general. Providing X-radiation having multiple photon energies may help differentiating tissue structures when generating X-ray images. Consequently, an X-ray generating device that allows the switching of a potential of an electron collecting element versus an electron emitting element for providing different energy modes is presented. According to the present invention, an X-ray generating device is provided, comprising an electron emitting element (16) and electron collecting element (20). The electron emitting element (16) and the electron collecting element (20) are operatively coupled for the generation of X-radiation (14). A potential is arranged between the electron emitting element (16) and the electron collecting element (20) for acceleration of electrons from the electron emitting element 16 to the electron collecting element (20), the electrons constituting an electron beam (7). The electron beam (17) is adapted to influence the potential.