Asymmetric PWM controlled LLCC resonant half bridge dual outputs LED driver

Abstract

Anasymmetric PWM controlled LLCC LED driver with capacitor connected in series with secondary windingof the transformer is proposed. Due to the presence of the secondary side resonant capacitor, the DC bias of the magnetizing current can be eliminated when asymmetric PWM control is employed. Because the switching frequency is fixed regardless of the load variation, the efficiency of light load is improved compared to conventional frequency controlled LLC topology, especially in dimming applications. The operating principle and circuit simplification of the secondary side circuit are presented. A two outputs LED driver prototype with 100V-200V output, 0.035A-0.35A/channel is built up to verify the theoretical analysis.