How can safety capacitors for power FTUs balance EMC and safety requirements?

Safety capacitors must meet both EMC filtering and safety insulation requirements. Design scheme: Capacitor X, CY-X2-474K (0.47μF/305V), is connected between L and N for differential-mode filtering, achieving UL and CE safety certifications. Capacitor Y, CY-Y1-222K (2.2nF/250V), is connected between L/G and N/G for common-mode filtering, meeting Y1 level (8kV surge). In PCB layout, safety capacitors are preferentially placed at the power input, forming a filter network with the common-mode inductor CMZ3225A-501T. Safety distances: Primary-secondary spacing greater than 8mm, creepage distance greater than 6.4mm. This design reduces conducted emissions by 35dB in the 150kHz-30MHz range while meeting IEC 60950-1 safety insulation requirements (3000VAC withstand voltage), ensuring safe and reliable FTU operation.