Simple and Effective Adaptive Deadtime Strategies for LLC Resonant Converter: Analysis, Design, and Implementation

Deadtime is a critical design target for soft switching dc/dc converters. On the one hand, the deadtime is necessary to ensure the safety operation of the devices in one switching leg; on the other hand, enough deadtime is required to achieve zero voltage switching (ZVS) operation. Due to the complexity of LLC converters, traditionally, the deadtime selection is either based on engineering experience or inaccurate analysis of the converter, which leads to an unoptimized deadtime. Specifically, a large deadtime will lead to efficiency degradation due to the body diode conduction during deadtime. The ZVS operation cannot be completely achieved with a small deadtime, which will also degrade the converter efficiency. Therefore, there is a demand for an accurate analysis of the deadtime effect on LLC converters. In this article, an accurate and in-depth analysis of the deadtime effect on the LLC converter is performed with the aid of the time-domain analysis (TDA). However, the proposed adaptive deadtime strategies can also be implemented based on the experiment or simulation results for those who do not have access to the TDA of LLC converters. Based on the analysis, novel adaptive deadtime strategies are proposed for the LLC converter. Compared with the traditional fixed deadtime strategy, around 1% efficiency improvement is achieved for a 125-W experimental prototype during the whole operating range.