Asymmetrical half-bridge converter with adaptive feedback compensation for dimmable LED lighting applications

This paper proposes an adaptive feedback gain compensation technique and simple PI control for an asymmetrical half-bridge (AHB) converter to solve slow system response problem due to the fact that the DC gain of the AHB converter depends on the duty cycle. The focus is on dimmable high brightness light-emitting diode (LED) applications subjected to disturbances or an immediate change of the reference output current from a dimming of the LED brightness or the case of a fault in the LED string. The curve fitting method is employed to address the nonlinearity of the adaptive feedback gain compensating parameters in the control loop. The system is implemented based on analog design, using only an additional low-cost operational amplifier. Experimental results obtained from a 60-W converter confirm the validity of the proposed method where the settling time of output current has been improved by 60-70% with the reduced overshoot. In additional, the system dynamic responses and performance are immune to duty cycle variation.