A high efficiency and power factor, segmented linear constant current LED driver

A high efficiency,high power factor,and linear constant current LED driver based on adaptive segmented linear architecture is presented.When the input voltage varied,the proposed LED driver automatically switched over LED strings according to the segmented LED voltage drop,which increased the LED lighting time.The efficiency and power factor are improved,while the system design is simplified by this control scheme.Without the usage of electrolytic capacitor and magnetic components,the proposed driver possesses advantages of smaller size,longer lifetime and lower cost over others.The proposed driver is implemented in 0.8 μm 5 V/40 V HVCMOS process,which occupies an active area of 820×920 μm~2.The measured results show that the average value of the internal reference voltage is 500 ± 7 mV,with a standard deviation of only 4.629 mV,thus LED current can be set accurately.Under 220 V root mean square 50 Hz utility voltage and the number ratio of the three LED strings being 47:17:16,the system can realize a high power factor of 0.974 and power conversion efficiency of 93.4%.