An Adaptive High-Precision OCP Control Scheme for Flyback AC/DC Converters

Flyback topology has been widely used in low-power applications due to its simplicity, wide input voltage range, low cost, and low standby power. However, conventional over current protection (OCP) control scheme in flyback converters cannot meet the high precision constant current (CC) requirement in battery charger and LED applications. The proposed adaptive high-precision OCP control scheme can be widely used in ac/dc flyback converters to improve their CC accuracy. It consists of an OCP-Comp circuit and a Vpump circuit to detect the primary current in current cycle and adjust it in next cycle adaptively. The proposed OCP control scheme has been implemented in a controller IC adding no extra pin and achieves a significant improvement in output current accuracy compared to conventional OCP schemes. Test results show that the output current variation of the proposed prototype is less than ±0.6% when the input line voltage changes from 85 to 265 Vac.