Analysis of a PWM-resonant DC-to-DC converter

When a parallel resonant tank is excited by a bipolar current pulse train a sinusoidal voltage develops across the tank whose amplitude depends on the duty cycle of the pulse train. An isolated secondary can be derived by applying the tank voltage to an isolation transformer whose magnetizing inductance acts as the resonance inductor of the tank circuit. A DC output voltage is obtained after rectification and filtering of the sinusoidal secondary voltage and regulation is achieved by controlling the duty-cycle of the pulse train. The sinusoidal nature of the voltage across the isolation transformer alleviates some of the noise problems associated with parasitic capacitances of an isolation transformer when operated with square voltage waveforms. The DC and small-signal analysis of the power converter is given and an equivalent small-signal circuit model is derived. Experimental results which confirm the validity of the model are presented