基于反激变换器恒流控制的电压前馈补偿策略

Strategy of Voltage Forward Feedback Compensation Base on Flyback Converter Constant-current Control

反激变换器因其结构简单,成本低廉,在小功率电源如手机充电器,笔记本适配器中得到广泛应用。在很多手机充电器的应用中,都要求充电器在达到额定电流之前保持恒压输出,超过额定电流之后保持恒流输出。由于开关管的传输延时,在不同的输入电压下,通常会导致原边峰值电流变化,这将严重影响副边恒流点的控制精度。本文详细分析了反激变换器工作在断续模式时,恒流特性受输入电压影响的原因,并介绍了三种消除输入电压影响的补偿方案,比较了这三种方案的优缺点。最后通过一个12 W的充电器样机,实验验证了加入电压前馈补偿之后恒流误差从2.8%降低至1.2%,取得了良好的补偿效果。

Flyback converter is widely used in low power supplies such as cellphone charger, notebook adapter due to its simple structure and low cost. Most of these applications require the converter regulating in constant-voltage mode before the rat- ed current, and transform to constant-current （CC） regulation when the output current exceed the rated. However, the primary peak current will vary in different input voltage because of the propagation delay of the MOSFET, resulting in the variation of constant-current point and reducing the CC regulation accuracy. The paper analyzed the reason of input voltage impacting the CC regulation when flyback converter working in Discontinuous Current Mode. In addition, three methods of eliminating the im- pact of input voltage are introduced and compared in the paper. Experiments results from a 12 W charge prototype indicated the CC regulation error have reduced to 1.2% from 2.8% with volt- age forward feedback compensation.