A conduction band control AC-DC Buck converter for a high efficiency and high power density adapter

This paper proposes a new control method for an AC-DC Buck converter which is utilized as a front-end converter of a 2-stage high power density adapter. It presents a theoretical analysis, a design consideration, and experimental results. In the conventional adapter applications, 2-stage configuration shows higher power transfer efficiency and higher power density than those of the single stage flyback converter. In the 2-stage AC-DC converter, the boost converter is widely used as a front-end converter. It provides continuous input current and power factor correction. However, an efficiency variation between high AC line and low AC line is large. On the other hand, the proposed conduction band control method for a buck front-end converter has an advantage of small efficiency variation. In the proposed control method, switching operation is determined by a band control voltage which represents output load condition, and an AC line voltage. In half of line cycle, if the instantaneous line voltage is lower than the band control voltage, the buck converter operates and transfers power to the downstream converter. On the contrary, if the instantaneous line voltage is higher than the band control voltage, the buck converter stops switching operation. Thus, the proposed control method reduces switching loss under high AC line and light load condition. A 60W prototype which is configured the buck and LLC converter with the proposed control method is experimented on to verify the validity of the proposed system. The prototype shows 92.16% of AC-DC overall efficiency and 20.19 W/in3 of power density.