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This paper presents a high dimming ratio light emitting diode (LED) drive controller chip with digital mode dimming (DMD). The chip is composed of a boost power converter and a dimming control block. A novel constant on time (COT) control strategy is proposed for boost converter to achieve high dimming ratio. In addition,a fast enough load transient response of the converter power stage ensures its high dimming ratio. The COT control circuit operates mainly based on two current-capacitor timers and a finite state machine (FSM). The LED drive con- troller chip is designed and fabricated in 1.5 μm bipolar CMOS-DMOS (BCD) process with a die area of 1.31×1.43 mm2. Experimental results show that the proposed LED drive system works well. And,as expected,the minimum LED dimming on time of 1.0 μs and the corresponding dimming ratio of 1000 : 1 at 1 kHz dimming frequency are successfully achieved.
This paper presents a high dimming ratio light emitting diode (LED) drive controller chip with digital mode dimming (DMD). The chip is composed of a boost power converter and a dimming control block. A novel constant on time (COT) control strategy is proposed for boost converter to achieve high dimming ratio. In addition, a fast enough load transient response of the converter power stage ensures its high dimming ratio. The COT control circuit operates mainly on two current-capacitor timers and a finite state machine (FSM ) The LED drive con- troller chip is designed and fabricated in 1.5 μm bipolar CMOS-DMOS (BCD) process with a die area of 1.31 × 1.43 mm2. Experimental results show that the proposed LED drive system works well. And, as expected , the minimum LED dimming on time of 1.0 μs and the corresponding dimming ratio of 1000: 1 at 1 kHz dimming frequency are successfully achieved.