Design Of A High-precision CV/CC AC-DC Controller Based On Primary Side Feedback

The 21 st century is an era in which the integrated circuit industry is booming,the power management chip is the most important component of integrated circuit design and it's the key to ensure the stable operation of electronic equipment.In order to effectively protect the performance of electronic products and extend the service life of the products,this paper designs a high-precision CV/CC flyback AD-DC converter based on primary feedback.In order to determine the realization of high-precision constant voltage and constant current control scheme,this paper first analyzes the key factors affecting the output voltage accuracy and output current accuracy.For the constant voltage operation mode,the problem of the sampling port oscillation caused by the leakage inductance resonance and the diode voltage on the secondary side of the transformer causes the sampling of the output voltage inaccurate.The demagnetization time middle sampling output voltage strategy is proposed.When the circuit operates in the constant voltage control mode,the converter adopts pulse width modulation mode,samples the transformer auxiliary winding voltage and compares it with the reference voltage to generate an error signal,and obtains the power tube turn-off singal by comparing the primary side inductor current sampling value and the error signal.In order to effectively improve the system efficiency,the load signal is judged by the error signal to adjust the system switching frequency.For the constant current operation mode,a two-stage sampling circuit and a dynamic threshold circuit are proposed,sloving the problem of the power tube transmission delay and the circuit logic delay which cause the primary inductor current peak exceed the limit and result output current inaccuracy.When the circuit is operating in constant current control mode,the converter still uses pulse width modulation and the system operates at the maximum switching frequency.The two-stage sampling circuit obtains the true primary inductor current peak value and generates a dynamic threshold voltage through the dynamic threshold circuit,and the primary side inductor current is compared with the threshold voltage to obtain the power tube turn-off signal,thereby realizing high-precision constant current.The chip designed in this paper uses the HHNEC BCD350 nm GE process,and builds a typical 5V/1A application for test and verification.The test results show that the system can work normally with the input voltage in the range of 85~265Vac,and the maximum static power consumption is only 65 mW.When the system works in constant voltage mode,the constant voltage accuracy is ±1.2%,the linear adjustment rate is ±0.4%,the load regulation rate is ±1.1%,and the minimum transmission efficiency is 74.7%.When the system works in constant current mode,it is constant.current accuracy is ±2%,the linear adjustment rate is ±1.7%,the load regulation is ±1.3%,and the minimum transmission efficiency is 70.0%.The above test data shows the converter designed in this paper meets the design specifications and has a good application prospect.