Novel frequency jittering control applied to energy-saving converters

The low cost and high efficiency of quasi-resonant flyback converters have resulted in their wide application as the main circuit topology in power-converters. Because conducted electromagnetic interference (EMI) at low frequency domain of conventional quasi-resonant (QR) flyback converters probably exceeds the EN55022 Class-B of EMI standards, this paper presents novel frequency jittering control as the solution. The spread spectrum energy is used to reduce the harmonic amplitude and decrease the average transmission characteristic in the low frequency range. The presented new method is implemented in a chip and therefore an external component is unnecessary for the circuit, and no additional cost is incurred. A 24-W quasi-resonant flyback converter is designed to verify the presented method. The experimental results show that the average conducted EMI at 642 kHz is significantly lowered by approximately 10.2 dB and thus easily meets Comité International Spécial des Perturbations Radioélectriques 22 (CISPR 22) standards.