Power factor corrected primary side regulated flyback controller for smart LED lighting system

Light emmiting diode (LED) lighting is becoming more and more popular in both commercial and residential lighting system for its energy-efficiency and environmental-friendly merits. For high end lighting system, dimming and color control are always required, which are known as smart lighting. In this paper, a cost-effective power factor corrected (PFC) flyback pre-regulator is presented for smart lighting application. To reduce system cost, it adopts primary side regulation (PSR) control, thus eliminates secondary side output sensing and opto-coupler in conventional isolated flyback PFC control circuitry. For PSR control, the output voltage is reflected to the auxiliary winding only during the secondary side diode conducting period. It is difficult to sense the output voltage when the secondary side diode conduction time is short, even more difficult during the light load and valley of input voltage. Adaptive blanking time (ABT) control is proposed to avoid fault sensing and keep precise output regulation under those circumstances. A 36w demonstration board with this control method was built. Test results showed that output voltage regulation is better than that without ABT control. Power factor (PF) of 0.96 and 7.6% of total harmonic distortion (THD) under 220V rms input, and PF of 0.99 and THD of 11.2% under 110V rms has been achieved. With the proposed idea, the IEC61000-3-2 THD control standard for lighting system is implemented in a low-cost way.