A NOVEL SELF-EXCITED FORWARD DC-DC CONVERTER WITH ZERO-VOLTAGE-SWITCHED RESONANT TRANSITIONS USING A SATURABLE CORE

A novel self-excited forward converter is proposed, The turn-on and tu rn-off of the switch are zero-voltage-switching with resonant transiti on, A saturable core is used to achieve the self-excitation and the ze ro-voltage-switched resonant transition, The voltage waveform across t he switch is trapezoidal with sinusoidal transitions, and the current waveform flowing through the switch is quasisquare. The switching loss es, the conduction losses and the stresses of the switch are significa ntly reduced in the proposed converter, The output voltage is determin ed by the ON duty ratio of the switch as in a PWM converter, Two metho ds to modulate the ON duty ratio are proposed, Both methods results in variable-frequency operation. Experiments on two 5 V, 20 A dc-dc conv erters show good performance.