Adaptive Frequency Control for ZVS Synchronous Boost Converters Operated in Average Current Mode

For a zero-voltage switching (ZVS) synchronous boost converter, the power stage efficiency undergoes significant limitation when the load is outside the ideal range. In order to achieve optimum efficiency at a range of load conditions, the magnitude of the resonant current must be controlled. The most effective method to control resonant current is to adjust the converter's switching frequency. Though methods have been proposed as a solution to this issue, they are not compatible with average current mode control. In this paper, a two-loop solution is proposed, in which both the converter duty cycle and switching frequency are controlled in order to maintain the desired average inductor current under the ZVS condition. In support of this new adaptive frequency control, theoretical analysis, design criteria, as well as experimental validation are provided.