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A floating buck controlled multi-mode dimmable light-emitting diode (LED) driver that uses a stacked NMOS switch is presented, which reduces static operational current and eliminates auxiliary winding to simplify design and cost. The accuracy of the output current benefits from the use of a line-voltage compensation technique which can mitigate the effect of line-voltage fluctuation on current consistency. The proposed LED driver is implemented in 0.5 \mum 5V/40 V backend 2P2M CMOS process and occupies a die size (with pads) of 1.17\times 0.84\ mm^2. The experimental results show that the proposed LED driver achieves peak power efficiency of 95.4% across a wide range of input voltage from 85 to 264 Vac and a wide range of series-connected load LEDs from 11 to 27. The worst-case line regulation and load regulation of the output current are 0.28% and 0.25%, respectively. Measurements further show that the startup time is only 34.8 ms at 220 Vac with 50 Hz-input and multi-mode dimming can be easily implemented. [ABSTRACT FROM AUTHOR]

An output voltage ripple aware design of different voltage ramp signal of voltage-mode CCM random frequency buck converter for conductive EMI reduction is presented. A mathematical analysis has been carried out to model the output voltage ripple of random switching converter. Simulations of the converter have been undertaken and measured results from the converter fabricated with a standard 0.35 \mum CMOS process verify the proposed design approach. From experimental results, a carefully designed ramp can reduce the output voltage ripple by more than 8 times without significant influence on the inductor current spectrum spread and any increment on the output filtering inductance and capacitance comparing to the conventional design. [ABSTRACT FROM AUTHOR]

A dual modulation technique to improve power conversion efficiency with minimal increase in output voltage ripple is presented. The worsening switching noise caused by parasitic resistance and inductance due to high-switching operation can also be alleviated by the proposed ac ripple detector. Furthermore, the dual modulation method can speed up the load transient response since the switching frequency can increase to 5 MHz during the transient period. At very light loads, the switching frequency is always kept higher than the acoustic frequency to avoid noisy sound. Experiment results show that the converter operates at 5 MHz using a small inductor of 1 \mu \H. The load transient response time is shorter than 3 \mu \s when load current changes from 150 to 450 mA or vice versa. Power efficiency is kept higher than 85% over a wide load current range. Specifically, light efficiency can be raised to about 45% above that of the conventional design. [ABSTRACT FROM PUBLISHER]