22.8 An AC-input inductorless LED driver for visible-light-communication applications with 8Mb/s data-rate and 6.4% low-frequency flicker

Light-emitting diodes (LEDs) are becoming the dominant lighting source over their conventional counterparts. Besides the benefits of high efficiency and long lifetime, LEDs also show great potential for high-speed data transmission because of their wide bandwidth (BW). In addition to offering general lighting, the light output can be modulated with fast-switched LEDs to achieve visible light communication (VLC). Though over 100Mb/s data-rate has been demonstrated with white LEDs in the laboratory, the high-frequency modulation is hardly supported by commonly used dimmable drivers with switching converters to regulate LED current. In these drivers, the changing slope of LED current is limited by both low loop BW and large inductors and capacitors [1]. The linear multiple-string LED drivers [2], free of inductors and big capacitors, theoretically can provide higher turn on/off speed. However, the light output of these drivers usually varies significantly at the double-line-frequency, which not only is considered as a harmful optical flicker, but also greatly affects the effectiveness of data transmission. The linear driver in [3] regulates the product of LED current and LED voltage to mitigate the optical variation, but a multiplier has to be added in the regulation loop, resulting in limited BW.