A simple method to reduce line current zero-crossing distortion (LCZCD) for single-stage flyback LED driver

For the primary-side-regulation (PSR) single-stage flyback LED driver operating in critical conduction mode (CRM), the input line current is notably distorted around the zero-crossing of the line voltage, especially in the conditions of high input voltage and light load. This paper derives the expression of the line current, and the reason of line current zero-crossing distortion (LCZCD) is investigated. After that, a simple method to reduce LCZCD is proposed by duty cycle limitation (DCL). The driving integrated circuits (ICs) with and without DCL are fabricated and the experimental results from LED drivers verify the effectiveness of the proposed method.