Universal Synchronous Rectification Scheme for LLC Resonant Converter Using Primary-Side Inductor Voltage

Abstract

In recent years, many advanced modulation strategies have been applied in LLC resonant converters, resulting in the increased demand for the synchronous rectification (SR) schemes without modulation strategy limitation. However, the conventional universal SR schemes are mainly on the basis of primary/secondary side current or drain-source voltage of synchronous rectifiers, which are limited by high cost of current transformer (CT) and loss of duty cycle caused by parasitic inductance, respectively. To deal with these problems, this paper proposes a novel SR scheme for LLC resonant converter. Firstly, a SR analysis method on the basis of the idea of power transmission is proposed. It can decouple SR from modulation strategy. Based on this method, this paper proposes a universal SR scheme using primary-side inductor voltage. The scheme is no longer restricted by the modulation strategy of converter. Meanwhile, no CT is required, thereby reducing the cost and conduction loss. Thanks to the large signal sensing-based, this scheme has good noise immunity. Moreover, it eliminates the negative effect of parasitic inductance by integral operation. With these effects, it has high accuracy of SR. Furthermore, an easily-debugged analog implementation is designed, which only needs to adjust one component parameter. Finally, experimental results show that the proposed scheme is compatible with different modulation strategies, and it has higher efficiency than the commercial SR scheme in a wide range of operating conditions.