Design Of A Highly Accuracy PSR CC/CV AC-DC Converter Without Auxiliary Winding

With the rapid development of electronic science and technology,electronic devices and products are becoming more and more widely used and their performance is getting higher and higher.At the same time,the market for power products has also grown rapidly.A good-performance power supply is critical to improve the performance of electronic devices.Current electronic market has increasing demands on power products.On the one hand,the performance of the power supply is hoped to be as good as possible,on the other hand,its cost is hoped to be as low as possible.Based on this market situation,this paper has done a deep research on the flyback converter,which is commonly used in low power applications,and has designed a high-performance,low-cost AC-DC CC/CV converter used for lithium battery chargers.The proposed converter adopts two-winding topology,and the system only contains primary and secondary sides.In the aspect of the constant voltage and current control,this paper designs a control method based on primary-side regulation.First,the reflected voltage of the output voltage is detected on the primary-side inductor,and the sampled feedback voltage is compared with a reference voltage.Then the error signal of them is obtained and amplified.Finally,the result and an exponential wave signal are modulated to adjust the switching frequency of the converter in a large range.Therefore,the output voltage can be kept constant under different input and load conditions.In the constant current output mode,the system first detects the demagnetization time from the feedback signal on the primary inductor,and then adjusts the demagnetization duty cycle of the system through the double demagnetization control module to achieve a constant output current under different operating conditions.In addition,based on the small signal modeling and analysis of the feedback loop of the entire system,a single-zero single-pole compensation network is designed,thereby adjusting the system bandwidth and phase margin,and improving the system’s dynamic response performance.In order to solve the chip powering problem of the two-winding topology,this paper proposed a method based on the base charge storage effect of the power bipolar transistor,and charging the chip power supply capacitor at the near end of the turn-on period.In addition,a hysteretic chip power control method is also designed to improve the power efficiency.For the output sampling problem,this paper proposed a primary-side inductor sampling method.On the one hand,the output current is sampled through zero-crossing detection of the feedback signal.On the other hand,the output voltage is sampled at 2/3 demagnetization time.Therefore,the constant voltage control and constant current control are both realized,and higher sampling accuracy is obtained.The control chip has been designed and taped out based on NEC 1 μm HVCMOS process,and a 5V/1A prototype has been built to verify its feasibility.Experimental results show that under the working condition of90Vac～265Vac input and full load,the deviations of output voltage and current are within ±1.3% and ±2.5%,while maximum conversion efficiency can reach a level of 78.9%.Besides,the control chip can be powered perfectly,and its power supply voltage can always be maintained between 5V～5.2V.Compared with the traditional three-winding topology,the proposed converter not only achieves higher output accuracy and conversion efficiency,but also saves one winding,making the number of peripheral devices less,the transformer simpler,and the system cost lower.