Primary-side controller IC design for quasi-resonant flyback LED driver

A primary-side quasi-resonant (QR) controller IC for single-stage flyback LED driver with high power factor (PF) and low total current harmonic distortion (THDi) is proposed in this paper. Conventionally, the flyback PFC converter with critical conduction mode QR control will suffer from higher switching loss and occur higher THDi at high line condition. To solve this problem, a frequency limit QR control is proposed and analyzed. By using the proposed control, the main switch of flyback converter is turned on with valley voltage switching and the maximum frequency is limited. So that the system efficiency is increased and the input current will follow the input voltage waveform better than that with the conventional control. Finally, this controller is fabricated with TSMC 0.25 μm CMOS high voltage mixed signal general purpose process and applied to an input voltage of 90~264 Vrms, output voltage of nominal 40 V, and constant output current of 600 mA/24W hardware prototype to verified the feasibility of the proposed control. The experimental result shows that the measured THDi is reduced from 10.5% to 3.3% at low line and 24% to 6.2% at high line compare to the critical conduction mode (CRM) QR flyback power factor correction (PFC) converter. The highest overall power efficiency is 91.4 %.