An Improved VDS Sensing-based Synchronous Rectification Scheme for LLC Resonant Converter Using Perturb & Observe Algorithm

Although VDS sensing-based synchronous rectification (SR) schemes have been widely studied, the parasitic inductance of synchronous rectifier is still the main problem affecting the performance of these schemes. To deal with this problem, this paper proposes an improved VDS sensing-based SR scheme for LLC resonant converter. In this scheme, the VDS signal of the synchronous rectifier is sensed to determine the turn-on time of the SR control signal. Different from the conventional VDS sensing-based schemes, the tuning of the turnoff time of SR control signal is decoupled from the VDS signal. The turn-off time is obtained entirely through a perturb & observe (P&O) algorithm. It can eliminates the negative effects of parasitic inductance. Based on this algorithm, the proposed scheme can achieve accurate tuning of the turn-off time with any primary-side modulation strategy. With these effects, the proposed SR scheme can be compatible with arbitrary primary-side modulation strategies of LLC converter, which is convenient for application in different scenarios. Experimental results show the effectiveness of proposed SR scheme in a wide frequency range and light-to-full load conditions.