LLC DC-DC Converter with Flyback-Operation for Expanding the Regulation Range

LLC DC-DC converter can achieve high power efficiency because ZVS operation is possible in wide load range. However, when the load is light, and the input voltage is high, the operating frequency is becoming too high. Therefore, it is not suitable for applications with a frequency limit. Furthermore, it leads to high dv / dt, leading to lower reliability as power supply and EMI problem. Therefore, in this paper, it is proposed a control method that maintains regulation while suppressing the frequency increase at the time of light load of the secondary side synchronous rectification LLC DC-DC converter. Only the control method applied to the conventional circuit. Since the operation is similar to the flyback converter, it is called "flyback-operation" In the prototype experimental circuit of 48 V / 5 V - 200 W specification, the input voltage range can be increased by 23% when the load current is 0.75 A.