Steady state voltage gain of flyback converters for high voltage low power applications

A significant influence of parasitics is perceived in high voltage low power flyback converters. The sinusoidal resonance between the magnetising inductance and the parasitic capacitance results in apparent deviations in voltage gain unlike the conventional flyback converter. This effect is predominant in case of very lightly loaded converter where the major portion of the input energy is consumed in charging the parasitic capacitances. The paper presents an analytical expression for steady state voltage gain of flyback converter in high voltage low power applications. Insight on sinusoidal resonance between the magnetising inductance and the parasitic capacitances is outlined and the effects of converter operating with fixed frequency is addressed. Profile of converter voltage gain and switch stress with variation in switching frequency is examined from which a range of frequency which offers optimal gain along with zero voltage stress during turn on is observed. A control scheme which deploys variable switching frequency thereby facilitating Zero Voltage Switching is investigated. Analysis of converter employing zero voltage switching scheme is carried out and the analytical equations governing the operation are derived. Simulation model and hardware prototype is built to validate the analytical results.