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Nonlinear phenomena in power electronic circuits are generally studied through discrete-time maps. However, there exist very few circuit configurations (like, for example, the current-mode-controlled dc-dc converters or current programmed H-bridge inverter) for which the map can be obtained in closed form. In this paper, we show that, in a voltage-mode-controlled dc-dc converter, if the switching is governed by pulse-width modulation of the first kind (PWM-1), an explicit form of the stroboscopic map can be obtained. The resulting discrete-time state space is piecewise smooth, divided into five regions, each with a different functional form. We then analyze the bifurcation behavior using the explicit map and demonstrate the different types of border collision bifurcations that may occur in this system as a fixed point moves from one region to another. This includes the very interesting case of a direct transition from periodicity to quasi-periodicity through the route of border collision bifurcation. Mode-locking periodic windows are also obtained at certain ranges of the parameters. The two-parameter bifurcation diagram is presented, showing the domains of existence of different oscillatory modes in the system parameter plane. [ABSTRACT FROM AUTHOR]