Abstract: With TOP243Y as control chip of multiplexed output flyback switch power supply,has the advantages of small volume,high integration and strong function,and the high-frequency transformer design and calculation large effect on the overall performance of multiple output the switch power supply.Based on the design computation using PI PIXls Designer 8 software to optimize the parameters of the transformer can be achieved to improve voltage accuracy,reducing the ripple effect.Seen from the experimental data and waveform of the switching power supply regulator,electromagnetic compatibility are good,meet the design requirements.