Adaptive Dead-time Algorithm for Reducing Body-Diode Conduction Loss in an LLC Resonant Converter

LLC resonant converters can achieve zero-voltage switching (ZVS) of the primary-side switches by utilizing the characteristics of the resonant tank, and are therefore widely employed in various power conversion applications requiring high efficiency. Conventional dead-time design methods for LLC resonant converters have mainly focused on determining a sufficiently long dead time to ensure ZVS, while body-diode conduction loss during the dead-time interval has received relatively limited consideration. To address this issue, this paper proposes an adaptive dead-time algorithm that estimates the time required to achieve ZVS according to the operating condition using the resonant current measured at the switch turn-off instant and adjusts the dead time based on the estimated value. The proposed algorithm is evaluated under abrupt load-change conditions, and the results confirmed that the dead time was appropriately adjusted according to the operating condition, thereby maintaining ZVS operation while minimizing the body-diode conduction interval. In addition, compared with the conventional fixed dead-time method, the proposed algorithm effectively reduced both body-diode conduction loss and total switch loss. In particular, the reduction in total switch loss was approximately 66.12~69.85 % at rated load, whereas it increased to approximately 82.37~85.79 % under light-load conditions, demonstrating that the loss-reduction effect of the proposed algorithm is more pronounced at light load.