Frequency jitter modulation method for quasi-resonant flyback converter to mitigate EMI

Quasi-resonant (QR) flyback converter is the one of the most desirable switching mode power supply for low power chargers due to its low cost and high efficiency. However, to maintain good performance of the converter, there is a trade-off among the design of efficiency, output ripple noise, stabilization and electromagnetic interference EMI. In this paper, a novel frequency jitter modulation method is proposed for variable frequency converter to both mitigate EMI and keep high efficiency. It is acquired by controlling both the turn on edge and the turn off edge of the QR flyback switch. Detailed operation principle of the proposed modulation method is analyzed. To verify the efficiency of the proposed method, a dedicated primary side controlling chip combined with the frequency jitter modulation method is fabricated. The experimental results demonstrated the QR flyback prototype controlled by the integrated chip has excellent EMI performance.