Research on working frequency of quasiresonant switching power supply

REN Dawei, HU Jianren
（Institute of Electron Devices & Application，Hangzhou Dianzi University，Hangzhou 310018, China）

Abstract: Quasiresonant(QR) switching power supply achieve the breakover of switching tube at zero voltage by using the theory of resonant. So it can reduce the loss at switching . Because the circult is working at critical conduction mode, the frequency of this switching power supply is changed with the input voltage and output load, which brings some trouble for design. In order to certain the optimum working frequency, the theory of QR zero voltage switching (ZVS) flyback was investigated. After analyzing the change of voltage on switch, the relation between the circuit parameter and time in different periods was established. And the formula for calculating the optimum working frequency was deduced. Finally, the experiment based on L6565 was tested. The experimental results show that the analysis lays the foundation for the futher more optimization.
Key words: quasiresonance(QR); zero voltage switching(ZVS); working frequency; flyback converter