A Constant Current Control Scheme for Primary-Side Controlled Flyback Controller Operating in DCM and CCM

Abstract

Primary-side regulation (PSR) flyback converters operating in discontinuous conduction mode (DCM) are widely used in low-power applications. In DCM, the peak current control method for PSR flyback is generally adopted to achieve constant current (CC) output. However, there are few effective schemes suitable for DCM and continuous conduction mode (CCM) operation of PSR flyback converters due to the difficulty in estimating the output information correctly, especially in the case of analog circuit control. In this article, a control scheme based on midpoint sampling method is proposed to achieve a high-precision CC control, which operates seamlessly as the operating mode switched between DCM and CCM. In order to verify the feasibility and performance of the proposed control, a control IC with the proposed CC control scheme has been implemented in 0.18 μm 5 V/40 V BCD process. The experimental results show that the deviation of the output current is within ±1.93% under different input and load conditions.