This paper addresses the problem of obtain a one-dimensional discrete-time map for the duty-cycle of a boost converter under current-mode control. This converter is widely used in the power supply industry. In practice, period-one operation is of interest from the engineering design point of view; however, nonlinear phenomena such as bifurcations and chaos can occur in switch-mode DC-DC converters under current-mode control basically. A discrete-time map for the duty-cycle is particularly useful because in the converters the duty-cycle is the control signal.