A > 89% efficient LED driver with 0.5V supply voltage for applications requiring low average current

A modified boost converter topology is proposed to achieve better than 89% efficiency as an LED driver for applications in which low supply voltage and low average current are desired such as in a photoplethysmographic (PPG) heart rate (HR) monitor device. The approach embraces pulsing of the LED current, and allows a highly digital implementation for varying LED brightness based on Pulse Density Modulation (PDM). Measured results indicate that the LED driver, which is implemented in 180nm CMOS along with an external inductor, achieves an output current range of 28uA to 1.3mA with 6 current settings while maintaining >89% efficiency over a supply voltage range of 0.5 to 0.6V.