科研之友
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摘要
A family of dimmable ac light-emitting-diode(LED) drivers fed from dc voltages, is presented in this paper based on zero-current-switching quasi-resonant converters. The proposed family of drivers is based on replacing the diode in the conventional converter topologies (i.e., buck, boost, or buck-boost) by a string of high-brightness LEDs (HB-LEDs). Hence, the HB-LED string will be working as the rectifier diode and the load,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 the reverse-recovery 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 eliminated. 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 converters are suggested to be used in a postregulator 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 constructed prototype with an output power of 7.5 W, that is able to achieve an electrical efficiency of 94.5% and a luminous efficacy of 110 lm/W at full load. Moreover, the analysis has been extended to a comparison in terms of reliability with the conventional topologies on a 700-h test.
- 出版日期2018-10
