My Flyback converter using the MPX2001 fails radiated EMI at 50MHz . What are the different techniques I can use to meet EMI standards?
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The noise at 30-50MHz is caused by the junction capacitance of the rectifier diode resonating with the leakage inductance of the transformer winding or the PCB trace inductance. This can be the main output winding, the bias winding, or the clamp network in the RCD Flyback. Therefore, a ferrite bead in series with the winding or diode can damp this resonance. The ferrite bead has to be properly selected to match the radiated frequency. Also, to lower the Q of the network to 2, the resistance of the bead should be half of the square root of the ratio of L over C.