Cycle-by-cycle average input current sensing method for LLC resonant topologies

Average input current is an important control parameter for many power supply control techniques, but it is difficult to obtain in LLC resonant topologies due to the irregular current waveform and the existence of circulation current. Conventional current sensing methods have low bandwidth and are inaccurate. This paper proposes a cycle-by-cycle average input current sensing method. It utilizes the series resonant capacitor to derive the average input current, thus is lossless, accurate, and low-cost. The proposed method can be extended to other topologies that include a series capacitor. Thus it is potentially advantageous in vast applications.