EMI reduction of switching power supply by frequency jitter

Frequency jitter is a technique to lower the EMI noise by spreading the noise energy around the main switching frequency. The RBW of IF filter in EMI receiver has great effects on the performance of frequency jitter. In this paper, a model and MathCAD calculation algorithm of IF filter and AV detector are build to exactly predict the peak amplitude reduction of switching power supply using frequency jitter. Based on frequency modulation theory and the EMI receiver model, the critical parameters of frequency jitter are selected optimally. A 65 W flyback converter with UC3842 has been built as a prototype, and the test results are given.