Series resonant converter with phase-controlled synchronous rectifier

A series resonant converter with a phase-controlled center-tapped rectifier is presented, including a description of operation and experimental results. This converter has two very desirable dualities. First, it achieves high efficiency at a very low output voltage. Second, it converts 200 V down to 3.3 V in a single stage, which is not common. The rectifier is driven by a synchronous inverter and has a digital control which adjusts the phase on the drive of the rectifier MOSFETs. The output voltage is regulated while maintaining a maximum of 89% efficiency and minimum of 70% efficiency for a 20% line swing and 50% efficiency for a load swing of 500% from full power. Experimental results are presented for a 30 W converter with a minimum DC input voltage of 200 V and an output voltage of 3.3 V. The center-tapped topology included a winding scheme that created large leakage inductances to maximize power transfer and allowed for high efficiency even at 3.3 V