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 froma 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.