  We investigate time-dependent electron current through a quantum dot under
external drive (pulses), coupled to leads at zero bias. Simple analytic
expressions for current, generated by periodic pulses of any shape, are
obtained without any use of the Floquet expansion. We demonstrate that the
current, follows a local quench, displays the transient and steady-state
behavior, which are described by the same universal function of an external
drive. The results are applied for an analysis of the current generated by
rectangular and linear form pulses, in comparison with ultra-fast pulses of
very high amplitude. Our results are also applicable for study of On-Demand
Single-Electron sources and laser driven junctions.
