Zero Voltage Switching Control Method for MHz Boundary Conduction Mode Converters

Boundary conduction mode or critical conduction mode is characterized by an inductor current that operates in the boundary between continuous conduction modes (CCM) and discontinuous conduction modes, making the converter switching frequency dependent on the converter operating conditions. The advantage of this operation mode versus CCM is achieving zero current switching (ZCS) conditions for the converter rectifier, which makes it possible to use silicon diode rectifiers without having a penalty due to reverse recovery issues. Moreover, the main switch turn-on loss is decreased due to ZCS conditions and valley switching operation. However, the penalty is an increased current stress in the circuit and an increased main switch turn-off energy loss. Implementation of the synchronous rectifier in boundary conduction mode (BCM) converters makes it possible to achieve zero voltage switching (ZVS) conditions by extending the synchronous rectifier conduction time after zero current condition in the inductor. High power density and high-efficiency MHz implementations have already been demonstrated in the literature; however, none of the proposed solutions solves the controllability issues of the synchronous rectifier switch. This paper proposes and validates a ZVS self-regulating control method for BCM converters operating in the MHz switching frequency range.