Abstract: A DC-DC buck converter controlled by naturally sampled, constant-frequency PWM is operated in continuous conduction mode. Its behavior under different circuit parameters is deeply studied in this paper, especially chaotic behavior and corresponding output performance. The transforming pattern of the system behavior from stable state to chaotic state is discovered via a cascade of period-doubling bifurcations of the output voltage in the bifurcation diagram and a cascade of periodic orbits in the u-i phase space with filter capacitor as a variational parameter. The fact that some special values of the circuit parameters may lead to chaotic behavior is validated. Performances of the output ripples from stable state to chaotic state are also analyzed in time domain and frequency domain respectively.According to the developing trend of spectral characteristics from period 1 to chaotic state,some important conclusions which will become a helpful tool for optimization design of DC-DC converter are given.

Key words: DC-DC buck converter, periodic orbits, chaos, Lyapunov index, spectral characteristics