LLC series resonant converter with auxiliary circuit for hold-up time

Although LLC series resonant converter has advantages of wide operation range and high efficiency, hold up time requirement makes it difficult to optimal design at normal operating condition, results in increasing transformer size and low efficiency. In this paper, LLC series resonant converter with auxiliary circuit is proposed. Compare with conventional LLC series resonant converter, higher gain at the same frequency can be achieved because the proposed converter has a current boost up capability. Therefore, even if ac line is turned off, switching frequency range of LLC series resonant converter can be reduced. With the auxiliary circuit, LLC series resonant converter can achieve high power density and high efficiency at normal operation condition.