EMI 產生分析及無Y電容充電器設計The EMI design of the charger without Y Capacitor Adlsong Abstract: Some general knowledge of EMI is introduced in this paper. The basic principle of causing differential mode and common mode current related conducted emissions of EMI in the switch mode power supply is discussed in detail through the relevant circuit theories and the sketch diagrams. The design of the cancellation inside the structure of the transformer is also presented and explained by the sketch diagram. The methods for reducing radiated emissions of EMI are described as well too. In the end the design for common mode inductor is offered. At present, Y capacitor is widely adopted inside SMPS including the cell phone charger to pass EMI tests. The usage of Y capacitor leads to the leakage current from input lines to outp……