Buck-type wide-range dimmable LED driver

For many LED applications, the dimming control is required in saving the energy consumptions. However, the wide-range dimming cannot be achieved due to the minimum on-time and switching frequency at low dimming level. In this paper, a buck-type wide-range dimmable LED driver is designed and implemented. According to the different percentage of dimming, the buck converter can operate in QR mode, frequency limitation with the valley switching, frequency reduction mode, and burst mode with the primary-side control scheme. By changing the parameters of the PI controller, the LED current can still be estimated precisely in burst mode. Therefore, the ideally linear wide-range dimming can be achieved by the proposed primary-side control scheme. Finally, the buck-type LED driver with the universal input voltages 90-264 Vrms applied to 42 V/ 8 W LED lamps is implemented. The dimming range is from 100 % to 1 %. The line regulations at 100 % and 1 % dimming are both lower than 5 %. The power factor is higher than 0.96 and the total harmonic distortion is lower than 20 % in the universal input voltage range. The highest efficiency is 94.67%.