AC-DC LED Drive Chip Loop Analysis And Design

Nowadays the world’s energy conservation and environmental situation isdeteriorating, while energy-saving lighting technology has got more and more publicattention. Many countries legislate to regulate lighting management. New lightingtechnologies are emerging today, LED lighting technology for its low powerconsumption, long life advantages destined to be the vanguard of them all.First, different modes, including Continuous Conduction Mode (CCM) andDiscontinuous Conduction Mode (DCM), and the Current Programmed Mode (CPM),are analyzed for basic principles and electrical characteristics. Using the averageprocessing method separately linearizes each model. Each of the small-signal equivalentcircuits is modeled, and frequency characteristics are analyzed.In compare with the single-loop control mode of the CCM mode and DCM mode,double-loop control peak current sampling DCM-CPM mode gets advantages indynamic response and compensation method. Also, CPM mode converter has a certaindegree of suppression for input disturbance, which is a natural priority for AC-DCconverters.Based on the above characteristics, the peak current sampling DCM-CPM mode isdecided for the LED driver system, the chip and external components parameters isdetermined, which meets the power, security and fewer external componentsrequirements. Using this model makes it possible to protect the power MOS withoutintroducing additional pins. For long lifetime requirement, ceramic capacitor is used forall the external capacitors. The reference, oscillator, error amplifier and overcurrentprotection circuit is designed and simulated to satisfy loop design demands.Finally, the whole system is simulated, to verify the control loop is workingproperly. There are also simulation results that show the input voltage and loaddisturbances of the loop are preferably inhibited.