A Quasi-Resonant Half-Bridge Converter with Synchronous Rectification

• Main Authors: Chieh-Ting Chen, 陳玠廷
• Other Authors: Yu-Kang Lo
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/nah24w

碩士 === 國立臺灣科技大學 === 電子工程系 === 102 === This thesis studies and implements a simple, high-efficiency power supply for low-power applications. Without any additional light-load control strategies, the efficiency performances at both light and heavy loads are satisfactory. The front stage is a boost power factor corrector (PFC) operating mainly under critical conduction mode to fulfill near zero-voltage switching for the switch and zero-current switching for the output diode. Around zero crossings of the input voltage, the PFC operates under discontinuous conduction mode to reduce the switching loss. The post stage is a quasi-resonant half bridge (QRHB) converter. Since the switching frequency is fixed, the output voltage regulation is achieved by the duty cycle modulation. During the dead times, the switch parasitic capacitor and the resonant inductor form a resonant tank. The switch is turned on at a relatively low valley voltage. The switching frequency at light load remains constant, rather than goes high. These contribute to low switching losses. Moreover, the secondary synchronous rectifiers help reduce the conduction losses. A 90-W prototype circuit is implemented with universal input voltage and a rated 19.5-V/4.62-A output. The light-load (20%-load) efficiency reaches 85% and the peak efficiency can achieve 92.61%.