The advantages of resonant power conversion, specifically reduced EMI, and high efficiency have been known for some time. To date the complex control and protection issues faced by engineers designing resonant converters has restricted their adoption in large volume production. One particular difficulty is that of maintaining the super-resonant operation or lagging power factor mode. Super-resonant operation has a number of key advantages in the Soft-switched, Multi-resonant, Zero current switched (SMZ) converters. Zero-Voltage Switching (ZVS) and Zero-Current Switching (ZCS) occur at switch ON and ZVS may be established at switch OFF. As regulation takes place by frequency modulation, a system has to be devised to maintain switching above resonance. Otherwise, hard switching, positive feedback, and (in severe cases) control-loop lock-up can occur. Several techniques for maintaining super-resonant operation are outlined with practical results. The limitations of each technique are discussed. The latest integrated solution to control and power switching in the SMZ converter, incorporating sub-resonant protection is introduced.
展开▼
