Research And Design Of Digitally Controled Flyback AC-DC LED Driver

In recent years,with the increasing attention to energy saving and environmental protection,as the fourth generation of lighting sources,LED has received widespread attention.LED has the advantages of high efficiency,energy saving,environmental protection,high reliability and long life.The performance of the driver circuit directly affects the service life and performance of the LED.Therefore,a mature driver circuit is a key factor for rapid LED promotion.With the continuous development of power supply technology,digital control has become a hot spot in the field of switching power supplies due to its more flexible digital control,short design cycle,low process dependence,strong anti-interference ability,good portability,and in line with the development trend of switching power supplies.Therefore,the research on LED driving power technology not only has academic value,but also has practical value.By analyzing and comparing the structure of the switching power supply and its working principle,this paper adopts the flyback structure of the primary feedback and realizes the constant current function through the digital control method.Firstly,by analyzing the working principle of the flyback structure,the parameters of the power stage circuit are determined;Second,control-level circuits are implemented through Verilog.The control level circuit is divided into modules according to the function,divided into soft start,constant current control,soft switch,peak voltage and pwm signal generation module.After power-on,the circuit works in the soft-start phase.The digital soft-start module of this article can control the output current to increase steadily,effectively avoiding the output overshoot and the surge phenomenon;when the circuit works in the constant-current phase,the demagnetization time of the transformer and the switching period are detected cycle-by-cycle,and the primary peak current is controlled to achieve a constant current function;the soft-switching module realizes soft-switching operation by detecting the voltage information on the auxiliary coil for controlling the constant-current phase switching tube.The peak voltage and pwm signal generation module controls the circuit by detecting the operating state of the circuit.The LED driver circuit is implemented using SMIC 0.18μm BCD process.The circuit is simulated based on the Cadence Spectre platform.The simulation results show that the driver circuit can operate at a clock frequency of 50MHz and a switching frequency of40KHz.The input voltage within the range of 110-220Vac,the constant current output can be realized within 400-1000mA.The system efficiency can reach up to 89.1%,the maximum output current ripple value is 0.32%,and the ripple minimum is only 0.26%.The load adjustment rate is less than 1.33%,and the linear adjustment rate is 13%at the lowest.The simulation results show that the driver circuit can achieve a constant current output function in a wide range,and the constant current characteristics are good.Moreover,the circuit is insensitive to changes in the load and the input voltage,and the output current ripple is extremely low,which is suitable for the LED driver circuit.The logic part of the algorithm part is synthesized by Design Compiler software.The synthesis shows that the algorithm can meet the timing requirements and has a margin of more than 5ns.Based on the IC Compiler software platform for physical design,the digital part layout area is 287069.52μm~2.Building board-level circuits for functional verification can realize LED driver circuit functions.