No-Load Power Reduction Technique for AC/DC Adapters

The burst-mode control is generally used to regulate the output voltage of the ac/dc adapter under either lighter no-load condition. Although the burst-mode control reduces the switching loss, the control-IC and the feedback circuit at the output side still consume a large amount of power. In order to further reduce the power consumption at no-load condition, a no-load power reduction technique for ac/dc adapters is proposed in this paper. At first, the proposed technique employs a control-IC ON/OFF scheme to reduce the power consumption of the control-IC while the gate signal of primary power switch is idle. In addition, an out-put voltage drop scheme is adopted to cut down on the loss of the feedback circuit because the output voltage of the ac/dc adapter is not required to be regulated when the ac/dc adapter is disconnected from the load system. Thus, the proposed technique can greatly reduce the no-load power consumption below 30 mW. To verify the validity of the proposed technique, loss analysis and experimental results of 65 W/17.5 V ac/dc adapter are presented.