A computationally efficient computer large signal simulation of thyristor chopper circuits is presented. Nonlinear circuit models are used to represent the active circuit components in a Gear iteration algorithim. The forced steady-state response of the system is found by linearizing the system at each time step and evaluating the equivalent state transition matrix. In addition, the steady-state junction temperatures of the active devices are determined and used to modify the device characteristics accordingly. Finally, sample results for a simple chopper system are presented. Due to the general nature of the algorithims employed, the simulation program has a wide range of application.