The WT7131A is a high-performance synchronous rectification controller. It is used to control a secondary-side synchronous rectification MOSFET in a flyback switch mode power supply. Without external auxiliary winding supplies, the WT7131A can easily provide power to the VDD. It can be powered by either the VIN or VD pin. The WT7131A built-in several circuits to minimize external part counts and overall total system cost.