LLC converter with Taiwan Tech voltage doubler rectifier (LLC-TVD) for large-size LED-backlit LCD display applications

Employing Taiwan Tech voltage doubler rectifier, an enhanced LLC resonant converter (LLC-TVD) is proposed. In addition to having zero-voltage switching operation on the MOSFETs and zero-current switching on the rectifier diodes inherited from its predecessor, the proposed converter has several additional features. For instance, the rectifier diodes are clamped to the output voltage due to the utilization of the voltage doubler technique, the recovery of the transformer secondary leakage energy, and the lack of filter inductor. A smaller transformer secondary-to-primary turns-ratio can thus be applied leading to decreasing the conduction losses. Moreover, output capacitors are significantly reduced because of its built-in output voltage ripple cancellation mechanism. Consequently, film capacitor can be used instead of electrolytic capacitor resulting in achieving long life performance. In addition to the descriptions of the operation principle, theoretical analysis, and design considerations, a high frequency with 300-400-V input and 200V/200W output specification is realized by an LLC with conventional voltage doubler rectification circuit (LLC-VD) and the proposed LLC-TVD. The performance comparisons are made to demonstrate the superiority of the LLC-TVD over the LLC-VD.