1. A method for simulating transient conditions in a circuit using a piecewise constant model, the method comprising the steps of: evaluating an error criteria to determine a maximum allowable change in one of a current and a voltage, including replacing a plurality of predefined steps of the piecewise constant model; simulating the transient conditions by implementing an adaptive step in the piecewise constant model according to the maximum allowable change; and analyzing the circuit based on a result of the simulating.