A dual-path, current-sensing resistor-free boost LED driver with fast PWM dimming

A boost LED driver features high PWM dimming ratio and optimized efficiency is presented. This LED driver, which having low dropout voltage and is able to drive 3~7 LEDs in series with constant output current and fast PWM dimming, is alternative for brightness adjustment. A dual-path control scheme with automatically state switching and maintenance is proposed. Meanwhile, a cascode current mirror structure is adopted with the output transistor multiplexed as LED PWM dimming transistor. Implemented in 0.5um 25V BCD process, the measurement results show that a voltage conversion range of 5V input to 6~21V output with constant output current is achieved. With automatically switching dual-path control and optimized current mirror, the response time during PWM dimming is reduced to as less as 240ns and the efficiency is kept above 89% over wide PWM dimming ratio @250mA output current.