A Novel Synchronous Rectifier Driving Scheme for LLC Converter Based on Secondary Rectification Current Emulation

In conventional synchronous rectifier (SR) driving schemes, the drain to source voltage of SR is detected to generate its driving signal. However, the driving signal by this method will lose a portion of duty cycle due to the parasitic inductance in SR package and on-board parasitic inductance. This phenomenon is severe under heavy load and deteriorates the efficiency of the converter. In this article, a novel
LLC
SR driving scheme based on secondary rectification current emulation is proposed. An auxiliary winding of the transformer and an auxiliary winding of the resonant inductor located on the secondary side are in series to generate a superposed voltage signal. The secondary rectification current is emulated out according to the superposed voltage signal by an integration circuit. After that the SR driving signal, which is not affected by parasitic inductance, is generated with a logic circuit. Detailed theoretical analysis and circuit implementation have been presented. Finally, a 400 V input and 12 V/20 A output half-bridge
LLC
resonant converter prototype has been built up to verify the feasibility of the proposed SR driving scheme.