Abstract：The primary side feedback can stabilize the output voltage，and improve the service life of the

equipment without using the secondary winding detection error signal. The topology of active filter and the

improved method of primary side feedback were adopted. The performance of active EMI filter topologies was

analyzed from insertion loss and equivalent circuit，the active filter with voltage sampling and current compensation

was adopted. Through describing the mechanism of primary-side feedback of sampling knee point voltage，the

small signal modeling of the converter in discontinuous current mode（DCM） was carried out，and the

compensation network was designed to ensure the stability. The simulation and experimental results show that the

active EMI filter can effectively replace the traditional filtering method，and the original side feedback method can

detect and correct the output voltage fluctuation to ensure the voltage stability.

      Key words：power converter；small signal model；primary side feedback；active EMI filter