Design Of A Primary-side Controlled Offline Small Power Flyback LED Driver

With the looming global energy crisis and environmental pollution intensifies, energy saving has been firmly recognized by the people. LED lighting is gradually replacing traditional lighting such as incandescent, fluorescent and energy-saving lamps as fourth-generation lighting, because of LED lighting is energy saving, environmental friendly, long life, maintenance-free, easy to control, etc. With a road map of phase out incandescent light were set by countries, LED lighting technology got increasing attention and promotion. LED’s V-I characteristic requires constant current driving technique. The demands for traditional residential lighting promote offline low-power LED lighting technology becomes a research hotspot in recent years.This thesis introduces the traditional power converter topologies, control methods and modulation techniques at the beginning. Consider the wide application prospect of offline LED lighting and further reducing of the cost of the lighting system, the single-stage primary-side-regulation flyback topology has been adopted. The single-stage topology is relatively simple compared to the two-stage topology and with low bill of materials cost, but also has a larger output voltage ripple and poorer output current accuracy than two stage topology. The isolated offline topology can protect the flyback converter system from damages of high voltage and high current generated by power surges and the ground loop. The primary side feedback control method not only makes a tight system design by saving an optical coupler, but also improves the reliability of the design.A new type of leading edge blanking circuit with adjustable blanking time is proposed. Meanwhile a novel on-chip adaptive power MOSFET turn off delay detection circuit is designed in order to improve the line regulation of output current.The designed single-stage primary side regulated flyback constant current LED driving system was designed in Chartered 0.35um technology. The maximum switching frequency of the converter is less than 200 kHz. The new type of leading edge blanking time circuit with adjustable blanking time was integrated in the system. Completing system simulation with Cadence, converter conversion efficiency can reach up to 74.4%, the output power range is 5-13W; the line regulation can be improved from 23.2% to within 1.2% by adopted improved peak current sampling technique and a built-in adaptive power MOSFET turn off delay detection technique.