An adaptive on-time controlled boost LED driver with high dimming ratio
A high efficiency high dimming ratio boost LED driver without color shift issue is presented in this paper. The boost converter is controlled by an adaptive on-time (AOT) controller, using improved control stratagem based on constant on-time (COT) control, so as to realize fast transient response to achieve high dimming ratio. With AOT control, the operation frequency maintains constant under continuous current mode (CCM) and the output voltage ripple could be reduced. In addition, Pulse frequency modulation (PFM) is implemented automatically under discontinuous current mode (DCM) to improve the system efficiency. The chip was designed and implemented in 1.5 μm bipolar-CMOS-DMOS (BCD) process. The simulation and experimental results showed that the minimum dimming on-time could be reduced to 1.2 μs, which means a dimming ratio of 2000:1 is available at dimming frequency of 400 Hz.