A Synchronous Switching Method for a Variable Frequency ZVS Boost Converter

Using a synchronous FET in a DC-DC converter can mitigate diode conduction losses as the FET conduction voltage is much lower than the forward voltage of a diode. However, a synchronous topology does not feature natural self-switching of a diode rectifier. A common converter switching method achieves Zero Voltage Switching through Valley Switching in the Boundary Conduction Mode, using the natural self-switching of the output diode to indicate current decaying to zero, however a synchronous topology is more complex to implement with this method. In this paper, a novel method of implementing a synchronous FET with the Valley Switching method is presented, realized by predicting the inductor discharge time. An efficiency increase of up to 2.86% is found using the synchronous topology and an estimated 93.59% of diode conduction loss is mitigated. The method is designed for high efficiency emergency LED drivers.