Zero Voltage Switching Control Method for MHz Boundary Conduction Mode Converters

Boundary conduction mode (BCM) or critical conduction mode (CrM) converter implementations have become very attractive since the introduction of gallium nitride (GaN) switches. This operation mode is characterized by an inductor current that operates in the boundary between continuous (CCM) and discontinuous conduction modes (DCM) 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 (Si) based 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 synchronous rectifier in 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, 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 work proposes and validates a ZVS self-regulating control method for BCM converters operating in the MHz switching frequency range.