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 light- or 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 output 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 30mW. To verify the validity of the proposed technique, loss analysis and experimental results of 65W/17.5V ac/dc adapter are presented.