An Elimination Scheme of Long and Short Periods for Flyback Converter

For small size, low cost, and wide power range, the constant current (CC) control scheme suitable for both discontinuous conduction mode and continuous conduction mode (CCM) is prevalent in low and medium power applications. However long and short periods (LSP) emerge due to the inner control relationship of conventional flyback converter especially in CCM. An adaptive over current protection (OCP) control scheme is adopted to eliminate LSP. A threshold regulator and a calibrated protector are used to correct the OCP threshold dynamically in the proposed OCP circuit. To verify the feasibility and performance, the proposed scheme has been implemented in $0.18~\mu \text{m}$ BCD process. The experimental results show that the LSP is eliminated and deviation of the CC is within ±1.04% under different input and load conditions.