This work proposes a methodology to estimate core losses under pulsewidth modulation (PWM) or de bias ripple voltage excitations. A special hysteresisgraph was built to measure toroidal samples under pulsed voltages. An experimental methodology, based on the principles of ferromagnetism, was implemented to investigate minor loop losses in toroidal samples of oriented and nonoriented FeSi. Triangular induction waveforms with constant dB/dt were generated. The results demonstrated that minor loops produced by PWM voltage, do not affect the major hysteresis loop losses nor the losses of other minor loops measured at different points of the major loop. In these experiments, minor loop losses under PWM voltage were very similar to minor loop losses under dc bias ripple voltage. Aspects of the behavior of minor loop losses as a function of amplitude and magnetic flux density are reported in this work.