Detailed analysis of a current-doubler rectifier for an LLC resonant converter with high output current

Current-doubler rectifiers are well-known in conjunction with double ended buck-derived isolated converters. One major purpose for its implementation is the reduction of power losses in the transformer secondary winding. The topic of this paper is an extension to this approach and presents a detailed analysis of a current-doubler rectifier used in an LLC resonant converter. The analysis uses the first harmonic approximation (FHA) approach, which tremendously simplifies the system model, leading to a linear circuit. The design constraints are worked out, such that the converter behavior remains unaltered by adding the current-doubler. By using this type of rectifier, the LLC efficiency can be improved over a traditional approach with a center tapped secondary winding. The secondary side power losses are reduced significantly and the drawback of an unequal coupling between the primary and either one of the two secondary windings is eliminated. Measurements on a prototype verify the analytical and simulation results.