Quasiresonant Control With a Dynamic Frequency Selector and Constant Current Startup Technique for 92% Peak Efficiency and 85% Light-Load Efficiency Flyback Converter

The proposed quasiresonant control scheme can be widely used in a dc-dc flyback converter because it can achieve high efficiency with minimized external components. The proposed dynamic frequency selector improves conversion efficiency especially at light loads to meet the requirement of green power since the converter automatically switches to the discontinuous conduction mode for reducing the switching frequency and the switching power loss. Furthermore, low quiescent current can be guaranteed by the constant current startup circuit to further reduce power loss after the startup procedure. The test chip fabricated in VIS 0.5 μm 500 V UHV process occupies an active silicon area of 3.6 mm
²
. The peak efficiency can achieve 92% at load of 80 W and 85% efficiency at light load of 5 W.