Noise-Tolerant LLC Synchronous Rectification Using Volt-Second Product

Synchronous rectification (SR) technologies for $LLC$ resonant converters are essential to high-power, low-voltage battery chargers considering the excessive current stress on the rectifiers. Mainstream SR controllers employ an adaptive approach that measures the drain–source voltage during the SR turn-on phase ( $v_{\text {ds.on}}$ ). However, $v_{\text {ds.on}}$ is low-magnitude and sensitive to the voltage across parasitic inductors and capacitors. The distortion of $v_{\text {ds.on}}$ causes SR mistriggering, undermining the efficiency. This article proposes a noise-tolerant SR strategy based on the volt-second product (VSP) of SR drain–source voltage in the turn-off phase and rectifier current conduction time. The proposed method determines SR ON-time using high-magnitude voltage signals, which are tolerant of parasitic effects. In steady-state operation, the VSP method reduces the SR ON-time error caused by circuit parasitic components, whereas in transient operation, the algorithm dynamically adjusts SR ON-time to maintain a safe operation margin, preventing rectifier reverse current flow. Details of the implementation and timing sequence are provided to demonstrate the simplicity and effectiveness of the VSP SR algorithm. Experimental results show that compared with conventional adaptive SR, the proposed VSP SR decreases the ON-time error by 64% in the above-resonance operation and removes the reverse current in the below-resonance operation, which reduces the total loss by 3%.