The Constant Current Control Circuit Design Of Primary-side-regulation Flyback Switching Power Supporting CCM/QR Mode

As compared with traditional lighting methods,LED has many advantages,such as superior longevity,high luminance efficiency,environment friendliness and so on.Since 21 st century has been more and more favored by the market such as residential lighting,commercial,etc.However,the constant current drive circuit of LED lighting system is not perfect enough especially in terms of output accuracy and conversion efficiency,it affects the further popularization of LED lighting.Therefore,there is great significance to research on LED drivers with high output precision,low power consumption and low cost.A constant current driver control circuit based on the primary-side-control flyback converter without auxiliary winding is proposed in this paper.Firstly,several topological structures of the flyback converter and several control modes to realize the constant output current are introduced,and their advantages and disadvantages are listed respectively.Next,after a detailed introduction to the PSR constant current driver with auxiliary,eliminating the auxiliary winding is proved to be feasible.After that a complete scheme of constant current control system based on the new non-auxiliary winding topology structure is proposed,and the internal module structure of this control circuit is also provided.Next,in order to make the constant current control circuit is workable both in CCM and QR mode,a new set of constant current modulation implementation scheme which integrated median sampling is proposed.At the same time,the control circuit adopts the structure of two cascaded power MOSFETS to replace the auxiliary winding in order to sample the demagnetization time so that the energy consumption of the system could be reduced further more.The control circuit also partially integrates the input cable compensation technology to improve the output current precision under different input voltage.In addition,the circuit also integrates over-temperature protection,the sampling resistor short-circuit protection and other protection circuits that improve both the reliable and the security of the system effectively.Finally,the design and simulation of each module circuit are completed by Cadence,and the functions of the whole constant current drive system are verified by PSIM.By setting the input voltage range to 85~220Vac,the output current to 1.5A and the maximum load to 12 V,the simulation results show that the average output current precision is within ±1.5% and its line regulation is less than ±2%,its load regulation is lower than ±1.5%,while the systematic conversion efficiency is above 85% under all working environments which meet the newly energy efficiency standards.