Zero-Voltage-Switching Multiresonant Technique-a Novel Approach to Improve Performance of High-Frequency Quasi-Resonant Converters

Recently-developed zero-current-switched quasi-resonant converters (ZCS QRC's) provide improved switching conditions for the power transistor by reducing its current to zero prior to turn off. The turn on, however, occurs when full input voltage is applied to the transistor, resulting in turn-on switching loss and noise. Zero-voltage-switched (ZVS) QRC's overcome this problem by shaping the transistor voltage for zero-voltage turn on. In ZVS QRC's, however, the power transistor suffers from excessive voltage stress and the converter regulation characteristics and stability are adversely affected by parasitic oscillations caused by the junction capacitance of the rectifying diode. A novel, multiresonant switch concept is proposed to overcome the problems of QRC's. The unique arrangement of a multiresonant network results in absorption of all major parasitic components in the resonant circuit, including transistor output capacitance, diode junction capacitance and transformer leakage inductance. This allows the new converters to provide favorable switching conditions for all semiconductor devices. Experimental results show that ZVS multiresonant converters are superior to ZVS QRC's due to reduced transistor voltage stress and improved load range and stability.