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A primary-side controlled universal-line flyback converter is widely used for its low-cost and low standby power advantages; however, conventional overpower protection schemes that feature primary-side control often experience inaccurate protection. In this paper, a novel scheme is presented, which achieves a very significant improvement in overpower accuracy while simultaneously meets a critical goal of adding no extra pin compared to conventional schemes when implemented in an IC. Experimental and simulation results verified the proposed strategy, and the scheme was implemented successfully in an IC.