Research And Design Of High-precision Miniaturized Flyback Converter

With the booming development of the consumer electronics market,great improvement has been made in power management technology represented by switching power supplies.However,the fast-growing Internet of Things and portable devices and other complex electronic systems have put forward more stringent requirements on switching power supply chips.In switching power supply circuits,due to its simple construction,nimble voltage conversion,and electrical isolation between input voltage and output voltage,flyback converters are one of the most popular topologies.According to the direct feedback or indirect feedback of the output voltage,the flyback converter has been divided into two main parts which are primary-side-feedback flyback converter and secondary-side-feedback flyback converter.The secondary side feedback flyback converter uses off-chip optocoupler components to directly sample the output voltage information from the secondary winding,which ensures high sampling accuracy,but increases the cost of peripheral components and reduces system reliability,which is unfavourable for the miniaturization of the flyback converter.So the high-precision and miniaturized primary-side feedback flyback converter has more economical use value.The main research goal of this paper is high-precision and miniaturized primaryside-regulation flyback converter.The primary-side-feedback flyback converter receives information of output load indirectly from the auxiliary winding or the primary winding for the negative feedback control of the system loop,which ensures the constant of the output voltage and has the limitation of low precision.This paper designs a knee-point voltage sampling circuit with higher accuracy based on the ripple comparison and the delay time compensation method so as to elevatet the output degree of accuracy,which can precisely gain the output voltage information.In addition,due to the existence of rectifying diodes,the sampled output voltage information will contain the rectifying diodes’ forward voltage,and its temperature characteristics will lead to a large deviation when the system is applied in a wide temperature range,so it is necessary to compensate the temperature to eliminate the error.In view of the miniaturization application requirements,the main limitation of the primary-side-feedback flyback converter lies in the auxiliary winding,loop compensation module and power tube modules outside the chip.In this paper,the structure of the primary side winding without auxiliary winding,directly on the side of the knee point sampling to avoid the use of auxiliary winding.Secondly,for the design of compensation circuit,the compensation scheme can be realized on chip by using the switching capacitor compensation scheme.Finally,the appropriate drain-source voltage clamp circuit and the on-resistance current of the power tube are selected,so the sampling scheme can integrate the power tube into the control chip to realize the design of miniaturized flyback converter.Firstly,the basic working principles and various control methods of the flyback converter has been introduced in this article.And then the analysis of the system design thoughts for the high-precision miniaturized flyback converter and the building of system power-level model which provides a stable loop compensation scheme were performed.Next,this article shows the detailed analysis of key sub-module circuits to ensure high precision and miniaturization and Cadence software simulation verification.Finally,the design scheme of this paper has been verified by the overall simulation under the 0.18μm60V BCD process.The simulation results verify that the output accuracy of the system is above 98% in the full load range,and the peripheral components of the system are greatly reduced,which means that the design has achieved the original intention target.