轻载下不存在电流倒灌现象的正激同步整流电路研究

A Study of Non-existent Current Intrusion in Forward Synchronous Rectifier Circuit under the Condition of Light Load

为解决轻载下正激变换器电压自驱动同步整流电路Buck滤波电感电流倒灌造成电路效率下降问题,本文在分析了常用正激变换器拓扑去磁复位时间与Buck滤波电感电流回零时间关系基础上,找出了电流倒灌原因,提出了在承担续流功能的同步整流MOS管驱动电路中增加有源快速放电电路,使主变压器激磁磁通复位后强迫同步整流MOS管迅速截止,避免轻载下电感电流倒灌现象.试验样机测试结果表明:本文提出的同步整流驱动方式可行、有效.

To overcome the reduction of efficiency of circuit caused by the Buck filter inductor current flow backward in the circuit of voltage self-driven synchronous rectifier under light load, the relation between the demagnetization reset time of common forward converter topology and the current of Buck filter inductor back to zero time is analyzed. Based on this relation, the reason of the Buck filter inductor current flowing backward so that the forward converter with voltage self-driven synchronous rectifier circuit works at light load have been found. An active fast discharge circuit is proposed to be added in synchronous rectifier MOS transistor driven circuit whose function is freewheeling. And this circuit forces synchronous rectifier MOS to close rapidly after the magnetic field flux of main transformer reset. Thus it can prevent the inductor current flow backward. The prototype test results show that this design has been verified effective and feasible by the experiment result.