An active-clamping resonant flyback DC/DC converter with improved output power transfer

In this paper, an active-clamping resonant flyback (ACRF) DC/DC converter is proposed. Two switches at the primary side of a single transformer are operated with pulse width modulation (PWM) at zero voltage switching (ZVS) turn-on condition during the dead time between switching instants. On the secondary side of the transformer, two series-resonant circuits are connected to the load through a half bridge rectifying stage, in which the diodes are operated at zero current switching (ZCS) condition. The two series-resonant circuits provide power transfer to the output load in both positive and negative cycles of operation, resulting in increased output power transfer without using additional switching devices or techniques such as interleaving. The extended describing function procedure is used to develop the steady state and small signal analyses of the proposed converter. Frequency domain analysis is then employed to derive transfer functions for small signal variations of the converter variables. The results are used to develop a single-loop, voltage-feedback control scheme to regulate the output voltage. It is demonstrated that the circuit provides two degrees of freedom to regulate the output voltage through duty ratio and switching frequency control. It is also shown that a single-loop, voltage-feedback control scheme is effective in regulating the output voltage.