99% High accuracy knee voltage detection for primary-side control in flyback converter

This paper proposed the adaptive knee voltage detection (KVD) technique to improve the output voltage accuracy of the primary side regulator. Owing to the insertion of the snubber circuit for reducing overshoot voltage, conventional KVD technique fails to get the output voltage information and thus to deteriorate the output voltage accuracy. Analysis of the snubber circuit and the resonance of the primary side can determine the band-pass filter in the proposed AKVD technique to get high accuracy output information without being affected by any kinds of resonances. Test chip designed in VIS 0.5μm BCD process demonstrates the accuracy of the output voltage higher than 99%. Besides, any abnormal detection won´t happen and thus the output ripple can be kept low.