This paper describes a simple-yet-effective control method for a DC-DC buck converter with voltage mode control (VMC), with a triangular wave generator (TWG) which regulates the slope of triangular wave based on the input and output voltages of the converter. Using the proposed TWG, both the load and line transient responses are improved. Since the TWG provides a line feed-forward control for the line transient response, it increases the open-loop bandwidth, and then better dynamic performance is obtained. Additional required circuit components are only a voltage controlled linear resistor (VCR) and a voltage controlled current source (VCCS). Compared with the conventional voltage control, the proposed method significantly improves the line and load transient responses. Furthermore this triangular wave slope regulation scheme is simple compared to digital feed-forward control scheme that requires non-linear calculation. Simulation results shows the effectiveness of the proposed method.