Effect of parasitics in high voltage bipolar flyback converter for lightly loaded resistive loads

In high voltage (HV) flyback charging circuits, the importance of transformer parasitics holds a significant part in the overall system parasitics. The resonance between magnetising inductance and resonant capacitance cause significant deviations in voltage gain. This effect is predominant in the case of very lightly loaded high voltage flyback converters when used for bipolar output voltages. In this paper, two circuit configurations are proposed to obtain the bipolar output voltage from a high voltage(HV) flyback for lightly loaded circuits. The operational similarities and the advantages/limitations of the two configurations are presented. The effect of transformer winding capacitance on the achievable gain in a bipolar operation is analysed in both the approaches. The analysis is verified in simulation and hardware implementation for high voltage bipolar flyback converters with valley mode switching to achieve minimum switching loss and device stress.