Study On A High Efficiency Low Output Voltage DC Power Supplies Based On CCM Flyback Converter With A New Driving Scheme

The high power density power supplies module is a high-tech product of switching-mode power supplies, so it is important to do some research works on it. To obtain the high converter efficiency is a main technology issue of switching power supplies. Synchronous rectification (SR) is necessary to achieve high efficiency in lower output voltage and higher output current application. If the proper Synchronous Rectification driving scheme is combined with the proper topology, the power dissipation of rectification will be reduced greatly. Synchronous rectification is most often applied to the Buck and Buck-drived isolated topologies, which are suitable for step-down, low-output-voltage applications. The flyback converter is well known for its simplicity. The supply voltage of IC is reducing constantly, and then the power dissipation of semiconductor diode is not accepted in the traditional flyback circuit, semiconductor diode is necessarily replaced by Synchronous Rectification to minimum voltage drop across it. The key issue of Synchronous Rectification is how to drive the Synchronous Rectifier properly for the high efficiency. When considering a gate-driver for a particular application, the converter topologies, switching conditions, voltage and current ratings as well as frequency of operation will all determine the suitability of the gate-driver for the application. A number of applications of the SR in the Flyback converter have also been reported. But the existed driving schemes are complicated and costly ,or they are not suitable for the wide input voltage application. These schemes cannot drive SRs properly and become the limitation for the Synchronous Rectification in the practice; then there would be more difficult and challengeable when it works in the Current Continuous Mode (CCM ) for flyback converter. So a novel driving scheme for Synchronous Rectification in CCM flyback converter is proposed in this paper; and it can be applied to the flyback converter in the CCM operation and wide input voltage range application. The new driving scheme possesses simple,cost-effective and high efficiency property. The circuit model and calculation of power dissipation is the key step for optimizing the converters. The steady state operating principle of flyback converter is analyzed detailedly, and the AC small signal model of CCM flyback converter is set up based on the State-Space Average method, it is verified by the simulation and experiment. The mathematic model of power dissipation in the CCM flyback converter is improved and verified by the experiment in this paper. Finally, the experimental prototype of 3.3V/3A with the proposed driving scheme was built, the highest efficiency is 88%, which is better than existed other driving schemes. It is concluded that the work in this paper is meaningful and worthful.