In the 2nd region, the switching frequency is higher than the lower resonant frequency but lower than
Fr1. Region ○2 is in the pink shaded area in Figure 4. The lower resonant frequency varies with load,
so the boundary of region ○2 and region ○3 traces the peak of the family load vs. gain curves. In this
complex region, the LLC resonant operation can be divided into two time intervals. In the first time
interval, Lr
resonates with Cr
and Lm is clamped by output voltage. When the current in the resonant