A fast and accurate method for the time-domain analysis of cyclically switching circuits with internally controlled switches is presented. At each time simulation step, by using the modified nodal method, the power electronics regulator is analyzed as a linear resistive circuit, obtained by replacing the energy-storing elements by dc independent sources of values equivalent to their charges at the respective moment. The resulting nodal voltage vector includes the signals controlling the state of the externally-controlled switches. No prior knowledge of the switches position is required. At each step, the algorithm monitors the position of each switch and checks the validity of the presumed state of the internally controlled switches, changing their state if necessary. DC parasitic resistances and forward voltage drops on switching elements are taken into account. No time-consuming operations, such as calculation of inverse Laplace transforms, are required. During each interval, the state is advanced by a simple integration. Experimental results confirmed the simulator's accuracy.