A novel, self-excited, PWM forward converter with ZVS resonant transition using two minor-loop-operated saturable cores

A self-excited forward power converter is proposed. The turn-on and turn-off transitions of the switch are zero voltage switched resonant transitions. Two saturable cores operated in minor B-H loop are used to achieve such transitions. The waveform of the voltage across the switch is trapezoidal, and the current flowing in the switch is a quasi-square-wave. The switching losses are considerably reduced, and the stresses in the switch are significantly suppressed. The converter has load characteristics similar to those of a square-wave pulse-width-modulated (PWM) forward converter. The on duty ratio is modulated by a small current applied to the winding of one core. Experiments on a 350 kHz, 100 W DC-DC power converter show good performance.<
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