High Cross-Regulation Multioutput $LLC$ Series Resonant Converter With Magamp Postregulator

A magnetic amplifier (Magamp) postregulator using a time-sharing control strategy is proposed when using a multioutput LLC series resonant converter. The operating principles of the proposed converter and the Magamp postregulator are analyzed in detail. Furthermore, the design criterion for the Magamp core is presented, and the dead-time problem of the Magamp postregulator is analyzed. Compared with a flyback converter, the dead-time impact in the LLC structure is much better for two main reasons. The first one is that there is no reverse-recovery resetting effect for the Magamp postregulator in an LLC topology, and the second is that, when the same dead time is applied in both converters, the effect is better by using an LLC topology than a flyback topology. Finally, an experimental prototype of 310-V input and 24-V/3-A and 18-V/2-A outputs was built and tested to verify the zero-voltage-switching (zero-current-switching) operation and the high cross-regulating ratio. The experimental results prove that the dead-time impact over a Magamp in an LLC converter is much better than that when using a flyback converter, since a high cross-regulating ratio was easily achieved without using complicate resetting methods or large dead load.