High frequency dc-dc AC-LED driver based on ZCS-QRCs

A boost dc-dc dimmable AC-LED driver is presented in this paper based on Zero Current Switching Quasi-Resonant Converters (ZCS-QRCs). The proposed driver is based on replacing the diode in conventional converter topologies (i.e. buck, boost or buck-boost) by a string of High-Brightness Light-Emitting Diodes (HB-LED). Hence, the HB-LED string will be working as the rectifier of the converter switching at the same frequency of the main switch. In this case, the output current, which is experimentally validated, shows a negative current peak due to the reverse recovery effect of the HB-LEDs. In order to reduce said effect on the HB-LEDs, the main switch of the proposed topologies is replaced with a full-wave resonant switch, which makes possible to reduce the di/dt during the turn-off of the HB-LED string, therefore the reverse recovery effect is minimized. Moreover, the dimming of the HB-LEDs is done by means of changing the switching frequency of the converter by varying the turn-off, while keeping a constant turn-on time. The proposed driver is suggested to be used in a post-regulator stage of an ac-dc converter or as the interface between the low voltage bus and the HB-LED string in a dc nanogrid. In order to validate the analysis, the proposed topologies have been experimentally tested on a dc-dc, AC-LED, ZCS-QRC, boost converter with an output power of 7.5 W constructed prototype, that is able to achieve a luminous efficacy of 110 lm/W at full load.