The bifurcation and chaos phenomena in a current mode controlled buck converter were explored,with the rectified output voltage as the input of the converter instead of a regulated ideal DC power supply.The mathematical model was developed under the continuous conduction mode.Considering the average value of DC input voltage as a variable,a set of bifurcation and chaos diagrams were given through computer simulation,when the converter is eguipped with regulated DC power supply and three rectified DC sources with different ripple content.The diagrams about inductive current and capacitor voltage were given and analyzed when the input comes from a rectified DC source with 10% ripple content.