Zero-voltage-switching technique in high-frequency off-line converters

Zero-voltage switching (ZVS) is implemented using a half-bridge (HB) topology for high-frequency offline applications. Two ZVS techniques are discussed: one is a quasiresonant technique (QRC) the other a multiresonant technique (MRC). A breadboarded HB ZVS-QRC is presented which operates from a 300±50 V input with maximum output power of 75 W (5 V, 15 A) and an efficiency of 83.5% at low line and full load and 79.2% at high line and full load. In ZVS-MRCs, all semiconductor devices are operated with no abrupt changes of the voltage across the devices. The technique permits utilization of junction capacitances of all semiconductor devices and the transformer leakage inductance to form a multiple-resonant-tank network to implement zero-voltage switching for all semiconductor devices. Employing this technique, a HB ZVS-MRC is breadboarded with the same specifications as the HB ZVS-QRC. The efficiency of the HB ZVS-MRC is slightly lower than that of the HB ZVS-QRC, 81.7% at full load and low line and 78.5% at full load and high line