A brushless DC dynamo includes a circular armature with N sets of first armature coils spaced with each other in sequence, N sets of second armature coils spaced with each other in sequence, a plurality of first wires and a plurality of second wires, and each first wire and each second wire respectively interconnecting between one set of the first armature coils and one set of the second armature coils; a control unit; a magnetic unit, disposed inside the circular armature unit, comprising a pair of magnetic poles, wherein the circular armature unit and the magnetic unit can rotate relatively to each other under control; and a position sensor for detecting the position of the magnetic unit, and outputting the information of magnetic unit's position to the control unit to trigger the control unit to output a control signal to control the first and second control switches.