A transformer model which consists of a nonlinear core with hysteresis and multiple windings is described as implemented in DSPICE. In contrast to previous implementations, the nonlinear behavior of the new model is described by continuous piecewise-hyperbolic functions characterized by three parameters. These parameters are the same as parameters previously published in the literature. A loop-traversing algorithm has been implemented which avoids discontinuities and eliminates both nonconvergence problems and the occurrence of erroneous voltage spikes during time-domain simulation. In the large-signal time-domain analysis the frequency-dependent eddy current losses in the core and wire losses are modeled. Additional effects, such as wire skin effect and temperature dependence, are also included. In the small-signal AC analysis the transformer is modeled as frequency-dependent lossy mutual inductors. For both analyses, the air gap and the elated fringe field effect are modeled by extending the magnetic path length of the core appropriately.>