Research On The Constant Current Digital Control Algorithm Of Primary-side Feedback Active-clamp Flyback Converter Output

Flyback converters are widely used in small and medium power applications due to their small size,simple structure,and low cost.Isolated active-clamp flyback converters can increase the switching frequency of the converter and have the characteristics of high power,small size,safety and reliability.It has been widely used in constant current occasions such as fast charging of mobile phones and notebook computers.The current isolated active-clamp flyback converter adopts an optocoupler feedback circuit,so problems such as nonlinearity,aging,temperature drift,and limited operating temperature range of the optocoupler cannot be avoided.The primary-side regulation control method can remove the optocoupler.However,due to the influence of converter parasitics,nonlinearity and single control method,the current isolated primary-side regulation active-clamp flyback converter scheme does not have a reliable method to achieve constant output current Control,and there is a problem of low light load efficiency.In view of the above problems,this paper proposes a low-cost digital control isolated primary-side regulation active-clamp flyback converter constant current control scheme.The main contents include(1)a charge balance control idea is proposed for constant current control output,which can be The nonlinear output diode current is equivalent to a regular linear waveform,and the parameters involved in the charge balance calculation are compensated to improve the system accuracy;(2)A new multi-mode composite digital control strategy with constant current output is proposed,with light load it adopting discontinuous conduction mode and valley switching control,medium load adopting continuous conduction mode and pulse frequency modulation control,and heavy load adopting continuous conduction mode and pulse width modulation control to realize the discontinuous conduction mode and continuous conduction mode in the full load range.Free switching removes the accuracy deviation introduced by the critical current mode;(3)Realizing the soft switching of the switching tube and reducing switching loss improve efficiency.In the discontinuous conduction working mode,realizing the valley switching strategy of the switching tube improves the efficiency of the entire system and achieves efficiency optimization.Using this optimization scheme,a high-precision,high-efficiency isolated active-clamp AC-DC converter stable multi-mode primary-side feedback digital control strategy can be obtained.According to the test results,the design in the full load range of constant current output is 3.20 A,the maximum output voltage load is 16 V,the accuracy of the current is ±2.3%.The average efficiency of the whole control system in the full load range can reach 85%,and the system multi-mode switching can be smoothly realized.In discontinuous conduction modulation,the trough conduction algorithm improves by more than 0.5%,so the test results can meet the design requirements.This scheme is of great significance for guiding the design of isolated AC-DC converter power supply and chip,and promoting the power increase and miniaturization development of isolated AC-DC converter.