An adaptive blanking time control scheme for audible noise free quasi resonant Flyback converter

The quasi resonant (QR) control scheme is widely adopted in Flyback converter to maximize its efficiency by reducing the switching loss. However, the maximum frequency limitation adopted in QR control may cause the audible noise due to the frequency hopping phenomena at certain load and input condition, which is related to the intrinsic output characteristic of the control scheme. This paper presents a simple solution to eliminate the frequency hopping in the QR Flyback using an adaptive blanking time circuit. The proposed method changes the blanking time automatically to keep the output characteristic smoothly which eliminate the audible noise in the transformer. The detailed operation principle and design considerations are presented. The experimental results from a 16V/4A prototype are provided to validate the effectiveness of the proposed solution.