Bang-Bang Charge Control for LLC Resonant Converters

This paper proposes a Bang-Bang Charge Control (BBCC) method for LLC resonant converters. Instead of switching frequency control, the BBCC method utilizes the series resonant capacitor voltage level to trigger the MOSFETs' switching actions. Advantages of the proposed method include fast dynamic performance and simple implementations. Small-signal analysis shows that the loop bandwidth can achieve around 1/6 of the switching frequency in all operating conditions. Experimental results show that 5 to 25 A load step transients are completed within only seven switching cycles at both 400- and 300-V input-voltage conditions. Practical considerations are also discussed in detail.