Research And Design Of High Precision Primary Side Control Flyback Converter

The primary side control flyback converter has many advantages such as low peripheral components,low cost and high reliability,and is widely used in low power adapters and offline battery chargers.However,the primary side control flyback converter cannot directly sample the output voltage,so the high precision primary side control flyback converter is a research hotspot.There are two common problems in the primary side control flyback converter.First,since the system has a delay including a sampling comparator rollover delay,a transmission delay,and a drive pull-down delay,the primary side peak current is larger than a preset value.Second,because the system has non-ideal factors including transformer leakage inductance and parasitic capacitance,the feedback voltage waveform is not ideal,and it is difficult to perform "knee point" sampling.In view of the above problems,the sample bus voltage is compensated for the primary peak current,which improves the constant current output control accuracy.In this t thesis,the leakage peak leading edge blanking(LEB)of the adaptive peak current and the dynamic leading edge blanking circuit can shield the ringing information caused by the leakage inductance and parasitic capacitance of the transformer to ensure the reliable operation of the system.At the same time,the ripple amplifier circuit amplifies the feedback voltage ripple information to obtain more accurate "knee point" information,which improves the output voltage resolution.In addition,this thesis also proposes a cable compensation circuit,high-precision sample and hold circuit to ensure the system constant voltage output control accuracy.First,the basic working principle of the flyback converter is ntroduced in this thesis,also the actual working waveform in the non-ideal case.Then the advantages and disadvantages of the primary side control flyback converter and the secondary side control flyback converter are introduced.Finally,the system architecture of the control chip designed in this thesis and the key module circuit to ensure the output control accuracy are reduced.The design details of the sub-module circuit are analyzed in detail and the simulation verification is made.In this thesis,the design and simulation of key sub-module circuits and chip verification are completed based on the 0.35?m 40 V BCD process.The simulation results show that the designed controller has achieved the expected constant output current and voltage regulating level.