The Analysis of Dead time's Influence on the Operating Characteristics of LLC Resonant Converter

LLC resonant converter typically works in Pulse Frequency Modulation (PFM) mode. The output voltage can be adjusted by adjusting the switching frequency of the converter. In order to meet wide voltage variation and various load conditions, the switching frequency of LLC converter must be changed in a wide range, which brings great difficulties to the design of high frequency transformer and the selection of power devices. Based on the analysis of the relationship between dead-time and operating characteristics of LLC resonant converter, this paper establishes the mathematical relationship between resonant tank gain and dead-time of LLC resonant converter, and makes theoretical analysis and experimental verification. The results show that without increasing the gain of the converter, increasing the dead-time appropriately can reduce the switching frequency range of the converter, thus reducing the design difficulty and the switching loss of the converter.