The protected surface conduction of topological insulators is in high demand for the next generation of electronic devices. What is needed to move forward are robust settings where topological surface currents can be controlled by simple means, ideally by the application of external stimuli. Surprisingly, this direction is only little explored and the role of topological states in such processes has remained obscure. In this work we demonstrate that we can boost the surface conduction of a topological insulator by light and/or electric field. This happens in a fully controlled way, and the additional Dirac carriers exhibit ultra-long live times. We provide a comprehensive understanding—carriers injection from the bulk to the surface states across an intrinsic Schottky barrier—and expect this mechanism to be at play in a broad range of materials and experimental settings.