An Improved Asymmetrical Half-Bridge Converter With Self-Driven Synchronous Rectifier for Dimmable LED Lighting

This paper proposes an adaptive feedback gain compensation technique and adaptive feedforward loop control based on analog design for an asymmetrical half-bridge converter without electrolytic capacitor to improve the system dynamic response and the system performance (i.e., low flickering and low ripple) for dimmable high-brightness light-emitting diode (LED) applications. In addition, an improved driving circuit of self-driven synchronous rectification (SR) is proposed for switching loss reduction at the secondary of the transformer. The control circuit is designed such that the SR metal-oxide-semiconductor field-effect transistor switch operates under zero-voltage switching (ZVS) mode while the driving signals are maintained within the acceptable voltage limits under duty cycle variations of the LED dimming applications. Simulation and experimental results obtained from a 60-W hardware prototype have confirmed the validity of the proposed method, where the settling time of the output current has been improved by 90% and the ripple of the output current has been reduced to less than 4% under rated current. The SR switches operate under ZVS condition throughout all operating regions where the maximum efficiency at 96.4% has been achieved.